dbcommands.c

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/*-------------------------------------------------------------------------
 *
 * dbcommands.c
 *      Database management commands (create/drop database).
 *
 * Note: database creation/destruction commands use exclusive locks on
 * the database objects (as expressed by LockSharedObject()) to avoid
 * stepping on each others' toes.  Formerly we used table-level locks
 * on pg_database, but that's too coarse-grained.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/dbcommands.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
 
#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/multixact.h"
#include "access/tableam.h"
#include "access/xact.h"
#include "access/xloginsert.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_database.h"
#include "catalog/pg_db_role_setting.h"
#include "catalog/pg_subscription.h"
#include "catalog/pg_tablespace.h"
#include "commands/comment.h"
#include "commands/dbcommands.h"
#include "commands/dbcommands_xlog.h"
#include "commands/defrem.h"
#include "commands/seclabel.h"
#include "commands/tablespace.h"
#include "common/file_perm.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "replication/slot.h"
#include "storage/copydir.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/md.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/guc.h"
#include "utils/pg_locale.h"
#include "utils/relmapper.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
 
/*
 * Create database strategy.
 *
 * CREATEDB_WAL_LOG will copy the database at the block level and WAL log each
 * copied block.
 *
 * CREATEDB_FILE_COPY will simply perform a file system level copy of the
 * database and log a single record for each tablespace copied. To make this
 * safe, it also triggers checkpoints before and after the operation.
 */
typedef enum CreateDBStrategy
{
    CREATEDB_WAL_LOG,
    CREATEDB_FILE_COPY
} CreateDBStrategy;
 
typedef struct
{
    Oid         src_dboid;      /* source (template) DB */
    Oid         dest_dboid;     /* DB we are trying to create */
    CreateDBStrategy strategy;  /* create db strategy */
} createdb_failure_params;
 
typedef struct
{
    Oid         dest_dboid;     /* DB we are trying to move */
    Oid         dest_tsoid;     /* tablespace we are trying to move to */
} movedb_failure_params;
 
/*
 * Information about a relation to be copied when creating a database.
 */
typedef struct CreateDBRelInfo
{
    RelFileLocator rlocator;    /* physical relation identifier */
    Oid         reloid;         /* relation oid */
    bool        permanent;      /* relation is permanent or unlogged */
} CreateDBRelInfo;
 
 
/* non-export function prototypes */
static void createdb_failure_callback(int code, Datum arg);
static void movedb(const char *dbname, const char *tblspcname);
static void movedb_failure_callback(int code, Datum arg);
static bool get_db_info(const char *name, LOCKMODE lockmode,
                        Oid *dbIdP, Oid *ownerIdP,
                        int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
                        TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
                        Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
                        char **dbIcurules,
                        char *dbLocProvider,
                        char **dbCollversion);
static void remove_dbtablespaces(Oid db_id);
static bool check_db_file_conflict(Oid db_id);
static int  errdetail_busy_db(int notherbackends, int npreparedxacts);
static void CreateDatabaseUsingWalLog(Oid src_dboid, Oid dst_dboid, Oid src_tsid,
                                      Oid dst_tsid);
static List *ScanSourceDatabasePgClass(Oid tbid, Oid dbid, char *srcpath);
static List *ScanSourceDatabasePgClassPage(Page page, Buffer buf, Oid tbid,
                                           Oid dbid, char *srcpath,
                                           List *rlocatorlist, Snapshot snapshot);
static CreateDBRelInfo *ScanSourceDatabasePgClassTuple(HeapTupleData *tuple,
                                                       Oid tbid, Oid dbid,
                                                       char *srcpath);
static void CreateDirAndVersionFile(char *dbpath, Oid dbid, Oid tsid,
                                    bool isRedo);
static void CreateDatabaseUsingFileCopy(Oid src_dboid, Oid dst_dboid,
                                        Oid src_tsid, Oid dst_tsid);
static void recovery_create_dbdir(char *path, bool only_tblspc);
 
/*
 * Create a new database using the WAL_LOG strategy.
 *
 * Each copied block is separately written to the write-ahead log.
 */
static void
CreateDatabaseUsingWalLog(Oid src_dboid, Oid dst_dboid,
                          Oid src_tsid, Oid dst_tsid)
{
    char       *srcpath;
    char       *dstpath;
    List       *rlocatorlist = NULL;
    ListCell   *cell;
    LockRelId   srcrelid;
    LockRelId   dstrelid;
    RelFileLocator srcrlocator;
    RelFileLocator dstrlocator;
    CreateDBRelInfo *relinfo;
 
    /* Get source and destination database paths. */
    srcpath = GetDatabasePath(src_dboid, src_tsid);
    dstpath = GetDatabasePath(dst_dboid, dst_tsid);
 
    /* Create database directory and write PG_VERSION file. */
    CreateDirAndVersionFile(dstpath, dst_dboid, dst_tsid, false);
 
    /* Copy relmap file from source database to the destination database. */
    RelationMapCopy(dst_dboid, dst_tsid, srcpath, dstpath);
 
    /* Get list of relfilelocators to copy from the source database. */
    rlocatorlist = ScanSourceDatabasePgClass(src_tsid, src_dboid, srcpath);
    Assert(rlocatorlist != NIL);
 
    /*
     * Database IDs will be the same for all relations so set them before
     * entering the loop.
     */
    srcrelid.dbId = src_dboid;
    dstrelid.dbId = dst_dboid;
 
    /* Loop over our list of relfilelocators and copy each one. */
    foreach(cell, rlocatorlist)
    {
        relinfo = lfirst(cell);
        srcrlocator = relinfo->rlocator;
 
        /*
         * If the relation is from the source db's default tablespace then we
         * need to create it in the destination db's default tablespace.
         * Otherwise, we need to create in the same tablespace as it is in the
         * source database.
         */
        if (srcrlocator.spcOid == src_tsid)
            dstrlocator.spcOid = dst_tsid;
        else
            dstrlocator.spcOid = srcrlocator.spcOid;
 
        dstrlocator.dbOid = dst_dboid;
        dstrlocator.relNumber = srcrlocator.relNumber;
 
        /*
         * Acquire locks on source and target relations before copying.
         *
         * We typically do not read relation data into shared_buffers without
         * holding a relation lock. It's unclear what could go wrong if we
         * skipped it in this case, because nobody can be modifying either the
         * source or destination database at this point, and we have locks on
         * both databases, too, but let's take the conservative route.
         */
        dstrelid.relId = srcrelid.relId = relinfo->reloid;
        LockRelationId(&srcrelid, AccessShareLock);
        LockRelationId(&dstrelid, AccessShareLock);
 
        /* Copy relation storage from source to the destination. */
        CreateAndCopyRelationData(srcrlocator, dstrlocator, relinfo->permanent);
 
        /* Release the relation locks. */
        UnlockRelationId(&srcrelid, AccessShareLock);
        UnlockRelationId(&dstrelid, AccessShareLock);
    }
 
    pfree(srcpath);
    pfree(dstpath);
    list_free_deep(rlocatorlist);
}
 
/*
 * Scan the pg_class table in the source database to identify the relations
 * that need to be copied to the destination database.
 *
 * This is an exception to the usual rule that cross-database access is
 * not possible. We can make it work here because we know that there are no
 * connections to the source database and (since there can't be prepared
 * transactions touching that database) no in-doubt tuples either. This
 * means that we don't need to worry about pruning removing anything from
 * under us, and we don't need to be too picky about our snapshot either.
 * As long as it sees all previously-committed XIDs as committed and all
 * aborted XIDs as aborted, we should be fine: nothing else is possible
 * here.
 *
 * We can't rely on the relcache for anything here, because that only knows
 * about the database to which we are connected, and can't handle access to
 * other databases. That also means we can't rely on the heap scan
 * infrastructure, which would be a bad idea anyway since it might try
 * to do things like HOT pruning which we definitely can't do safely in
 * a database to which we're not even connected.
 */
static List *
ScanSourceDatabasePgClass(Oid tbid, Oid dbid, char *srcpath)
{
    RelFileLocator rlocator;
    BlockNumber nblocks;
    BlockNumber blkno;
    Buffer      buf;
    RelFileNumber relfilenumber;
    Page        page;
    List       *rlocatorlist = NIL;
    LockRelId   relid;
    Snapshot    snapshot;
    SMgrRelation smgr;
    BufferAccessStrategy bstrategy;
 
    /* Get pg_class relfilenumber. */
    relfilenumber = RelationMapOidToFilenumberForDatabase(srcpath,
                                                          RelationRelationId);
 
    /* Don't read data into shared_buffers without holding a relation lock. */
    relid.dbId = dbid;
    relid.relId = RelationRelationId;
    LockRelationId(&relid, AccessShareLock);
 
    /* Prepare a RelFileLocator for the pg_class relation. */
    rlocator.spcOid = tbid;
    rlocator.dbOid = dbid;
    rlocator.relNumber = relfilenumber;
 
    smgr = smgropen(rlocator, InvalidBackendId);
    nblocks = smgrnblocks(smgr, MAIN_FORKNUM);
    smgrclose(smgr);
 
    /* Use a buffer access strategy since this is a bulk read operation. */
    bstrategy = GetAccessStrategy(BAS_BULKREAD);
 
    /*
     * As explained in the function header comments, we need a snapshot that
     * will see all committed transactions as committed, and our transaction
     * snapshot - or the active snapshot - might not be new enough for that,
     * but the return value of GetLatestSnapshot() should work fine.
     */
    snapshot = GetLatestSnapshot();
 
    /* Process the relation block by block. */
    for (blkno = 0; blkno < nblocks; blkno++)
    {
        CHECK_FOR_INTERRUPTS();
 
        buf = ReadBufferWithoutRelcache(rlocator, MAIN_FORKNUM, blkno,
                                        RBM_NORMAL, bstrategy, true);
 
        LockBuffer(buf, BUFFER_LOCK_SHARE);
        page = BufferGetPage(buf);
        if (PageIsNew(page) || PageIsEmpty(page))
        {
            UnlockReleaseBuffer(buf);
            continue;
        }
 
        /* Append relevant pg_class tuples for current page to rlocatorlist. */
        rlocatorlist = ScanSourceDatabasePgClassPage(page, buf, tbid, dbid,
                                                     srcpath, rlocatorlist,
                                                     snapshot);
 
        UnlockReleaseBuffer(buf);
    }
 
    /* Release relation lock. */
    UnlockRelationId(&relid, AccessShareLock);
 
    return rlocatorlist;
}
 
/*
 * Scan one page of the source database's pg_class relation and add relevant
 * entries to rlocatorlist. The return value is the updated list.
 */
static List *
ScanSourceDatabasePgClassPage(Page page, Buffer buf, Oid tbid, Oid dbid,
                              char *srcpath, List *rlocatorlist,
                              Snapshot snapshot)
{
    BlockNumber blkno = BufferGetBlockNumber(buf);
    OffsetNumber offnum;
    OffsetNumber maxoff;
    HeapTupleData tuple;
 
    maxoff = PageGetMaxOffsetNumber(page);
 
    /* Loop over offsets. */
    for (offnum = FirstOffsetNumber;
         offnum <= maxoff;
         offnum = OffsetNumberNext(offnum))
    {
        ItemId      itemid;
 
        itemid = PageGetItemId(page, offnum);
 
        /* Nothing to do if slot is empty or already dead. */
        if (!ItemIdIsUsed(itemid) || ItemIdIsDead(itemid) ||
            ItemIdIsRedirected(itemid))
            continue;
 
        Assert(ItemIdIsNormal(itemid));
        ItemPointerSet(&(tuple.t_self), blkno, offnum);
 
        /* Initialize a HeapTupleData structure. */
        tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
        tuple.t_len = ItemIdGetLength(itemid);
        tuple.t_tableOid = RelationRelationId;
 
        /* Skip tuples that are not visible to this snapshot. */
        if (HeapTupleSatisfiesVisibility(&tuple, snapshot, buf))
        {
            CreateDBRelInfo *relinfo;
 
            /*
             * ScanSourceDatabasePgClassTuple is in charge of constructing a
             * CreateDBRelInfo object for this tuple, but can also decide that
             * this tuple isn't something we need to copy. If we do need to
             * copy the relation, add it to the list.
             */
            relinfo = ScanSourceDatabasePgClassTuple(&tuple, tbid, dbid,
                                                     srcpath);
            if (relinfo != NULL)
                rlocatorlist = lappend(rlocatorlist, relinfo);
        }
    }
 
    return rlocatorlist;
}
 
/*
 * Decide whether a certain pg_class tuple represents something that
 * needs to be copied from the source database to the destination database,
 * and if so, construct a CreateDBRelInfo for it.
 *
 * Visibility checks are handled by the caller, so our job here is just
 * to assess the data stored in the tuple.
 */
CreateDBRelInfo *
ScanSourceDatabasePgClassTuple(HeapTupleData *tuple, Oid tbid, Oid dbid,
                               char *srcpath)
{
    CreateDBRelInfo *relinfo;
    Form_pg_class classForm;
    RelFileNumber relfilenumber = InvalidRelFileNumber;
 
    classForm = (Form_pg_class) GETSTRUCT(tuple);
 
    /*
     * Return NULL if this object does not need to be copied.
     *
     * Shared objects don't need to be copied, because they are shared.
     * Objects without storage can't be copied, because there's nothing to
     * copy. Temporary relations don't need to be copied either, because they
     * are inaccessible outside of the session that created them, which must
     * be gone already, and couldn't connect to a different database if it
     * still existed. autovacuum will eventually remove the pg_class entries
     * as well.
     */
    if (classForm->reltablespace == GLOBALTABLESPACE_OID ||
        !RELKIND_HAS_STORAGE(classForm->relkind) ||
        classForm->relpersistence == RELPERSISTENCE_TEMP)
        return NULL;
 
    /*
     * If relfilenumber is valid then directly use it.  Otherwise, consult the
     * relmap.
     */
    if (RelFileNumberIsValid(classForm->relfilenode))
        relfilenumber = classForm->relfilenode;
    else
        relfilenumber = RelationMapOidToFilenumberForDatabase(srcpath,
                                                              classForm->oid);
 
    /* We must have a valid relfilenumber. */
    if (!RelFileNumberIsValid(relfilenumber))
        elog(ERROR, "relation with OID %u does not have a valid relfilenumber",
             classForm->oid);
 
    /* Prepare a rel info element and add it to the list. */
    relinfo = (CreateDBRelInfo *) palloc(sizeof(CreateDBRelInfo));
    if (OidIsValid(classForm->reltablespace))
        relinfo->rlocator.spcOid = classForm->reltablespace;
    else
        relinfo->rlocator.spcOid = tbid;
 
    relinfo->rlocator.dbOid = dbid;
    relinfo->rlocator.relNumber = relfilenumber;
    relinfo->reloid = classForm->oid;
 
    /* Temporary relations were rejected above. */
    Assert(classForm->relpersistence != RELPERSISTENCE_TEMP);
    relinfo->permanent =
        (classForm->relpersistence == RELPERSISTENCE_PERMANENT) ? true : false;
 
    return relinfo;
}
 
/*
 * Create database directory and write out the PG_VERSION file in the database
 * path.  If isRedo is true, it's okay for the database directory to exist
 * already.
 */
static void
CreateDirAndVersionFile(char *dbpath, Oid dbid, Oid tsid, bool isRedo)
{
    int         fd;
    int         nbytes;
    char        versionfile[MAXPGPATH];
    char        buf[16];
 
    /*
     * Prepare version data before starting a critical section.
     *
     * Note that we don't have to copy this from the source database; there's
     * only one legal value.
     */
    sprintf(buf, "%s\n", PG_MAJORVERSION);
    nbytes = strlen(PG_MAJORVERSION) + 1;
 
    /* If we are not in WAL replay then write the WAL. */
    if (!isRedo)
    {
        xl_dbase_create_wal_log_rec xlrec;
        XLogRecPtr  lsn;
 
        START_CRIT_SECTION();
 
        xlrec.db_id = dbid;
        xlrec.tablespace_id = tsid;
 
        XLogBeginInsert();
        XLogRegisterData((char *) (&xlrec),
                         sizeof(xl_dbase_create_wal_log_rec));
 
        lsn = XLogInsert(RM_DBASE_ID, XLOG_DBASE_CREATE_WAL_LOG);
 
        /* As always, WAL must hit the disk before the data update does. */
        XLogFlush(lsn);
    }
 
    /* Create database directory. */
    if (MakePGDirectory(dbpath) < 0)
    {
        /* Failure other than already exists or not in WAL replay? */
        if (errno != EEXIST || !isRedo)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not create directory \"%s\": %m", dbpath)));
    }
 
    /*
     * Create PG_VERSION file in the database path.  If the file already
     * exists and we are in WAL replay then try again to open it in write
     * mode.
     */
    snprintf(versionfile, sizeof(versionfile), "%s/%s", dbpath, "PG_VERSION");
 
    fd = OpenTransientFile(versionfile, O_WRONLY | O_CREAT | O_EXCL | PG_BINARY);
    if (fd < 0 && errno == EEXIST && isRedo)
        fd = OpenTransientFile(versionfile, O_WRONLY | O_TRUNC | PG_BINARY);
 
    if (fd < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not create file \"%s\": %m", versionfile)));
 
    /* Write PG_MAJORVERSION in the PG_VERSION file. */
    pgstat_report_wait_start(WAIT_EVENT_VERSION_FILE_WRITE);
    errno = 0;
    if ((int) write(fd, buf, nbytes) != nbytes)
    {
        /* If write didn't set errno, assume problem is no disk space. */
        if (errno == 0)
            errno = ENOSPC;
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not write to file \"%s\": %m", versionfile)));
    }
    pgstat_report_wait_end();
 
    /* Close the version file. */
    CloseTransientFile(fd);
 
    /* Critical section done. */
    if (!isRedo)
        END_CRIT_SECTION();
}
 
/*
 * Create a new database using the FILE_COPY strategy.
 *
 * Copy each tablespace at the filesystem level, and log a single WAL record
 * for each tablespace copied.  This requires a checkpoint before and after the
 * copy, which may be expensive, but it does greatly reduce WAL generation
 * if the copied database is large.
 */
static void
CreateDatabaseUsingFileCopy(Oid src_dboid, Oid dst_dboid, Oid src_tsid,
                            Oid dst_tsid)
{
    TableScanDesc scan;
    Relation    rel;
    HeapTuple   tuple;
 
    /*
     * Force a checkpoint before starting the copy. This will force all dirty
     * buffers, including those of unlogged tables, out to disk, to ensure
     * source database is up-to-date on disk for the copy.
     * FlushDatabaseBuffers() would suffice for that, but we also want to
     * process any pending unlink requests. Otherwise, if a checkpoint
     * happened while we're copying files, a file might be deleted just when
     * we're about to copy it, causing the lstat() call in copydir() to fail
     * with ENOENT.
     */
    RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE |
                      CHECKPOINT_WAIT | CHECKPOINT_FLUSH_ALL);
 
    /*
     * Iterate through all tablespaces of the template database, and copy each
     * one to the new database.
     */
    rel = table_open(TableSpaceRelationId, AccessShareLock);
    scan = table_beginscan_catalog(rel, 0, NULL);
    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        Form_pg_tablespace spaceform = (Form_pg_tablespace) GETSTRUCT(tuple);
        Oid         srctablespace = spaceform->oid;
        Oid         dsttablespace;
        char       *srcpath;
        char       *dstpath;
        struct stat st;
 
        /* No need to copy global tablespace */
        if (srctablespace == GLOBALTABLESPACE_OID)
            continue;
 
        srcpath = GetDatabasePath(src_dboid, srctablespace);
 
        if (stat(srcpath, &st) < 0 || !S_ISDIR(st.st_mode) ||
            directory_is_empty(srcpath))
        {
            /* Assume we can ignore it */
            pfree(srcpath);
            continue;
        }
 
        if (srctablespace == src_tsid)
            dsttablespace = dst_tsid;
        else
            dsttablespace = srctablespace;
 
        dstpath = GetDatabasePath(dst_dboid, dsttablespace);
 
        /*
         * Copy this subdirectory to the new location
         *
         * We don't need to copy subdirectories
         */
        copydir(srcpath, dstpath, false);
 
        /* Record the filesystem change in XLOG */
        {
            xl_dbase_create_file_copy_rec xlrec;
 
            xlrec.db_id = dst_dboid;
            xlrec.tablespace_id = dsttablespace;
            xlrec.src_db_id = src_dboid;
            xlrec.src_tablespace_id = srctablespace;
 
            XLogBeginInsert();
            XLogRegisterData((char *) &xlrec,
                             sizeof(xl_dbase_create_file_copy_rec));
 
            (void) XLogInsert(RM_DBASE_ID,
                              XLOG_DBASE_CREATE_FILE_COPY | XLR_SPECIAL_REL_UPDATE);
        }
        pfree(srcpath);
        pfree(dstpath);
    }
    table_endscan(scan);
    table_close(rel, AccessShareLock);
 
    /*
     * We force a checkpoint before committing.  This effectively means that
     * committed XLOG_DBASE_CREATE_FILE_COPY operations will never need to be
     * replayed (at least not in ordinary crash recovery; we still have to
     * make the XLOG entry for the benefit of PITR operations). This avoids
     * two nasty scenarios:
     *
     * #1: When PITR is off, we don't XLOG the contents of newly created
     * indexes; therefore the drop-and-recreate-whole-directory behavior of
     * DBASE_CREATE replay would lose such indexes.
     *
     * #2: Since we have to recopy the source database during DBASE_CREATE
     * replay, we run the risk of copying changes in it that were committed
     * after the original CREATE DATABASE command but before the system crash
     * that led to the replay.  This is at least unexpected and at worst could
     * lead to inconsistencies, eg duplicate table names.
     *
     * (Both of these were real bugs in releases 8.0 through 8.0.3.)
     *
     * In PITR replay, the first of these isn't an issue, and the second is
     * only a risk if the CREATE DATABASE and subsequent template database
     * change both occur while a base backup is being taken. There doesn't
     * seem to be much we can do about that except document it as a
     * limitation.
     *
     * See CreateDatabaseUsingWalLog() for a less cheesy CREATE DATABASE
     * strategy that avoids these problems.
     */
    RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
}
 
/*
 * CREATE DATABASE
 */
Oid
createdb(ParseState *pstate, const CreatedbStmt *stmt)
{
    Oid         src_dboid;
    Oid         src_owner;
    int         src_encoding = -1;
    char       *src_collate = NULL;
    char       *src_ctype = NULL;
    char       *src_iculocale = NULL;
    char       *src_icurules = NULL;
    char        src_locprovider = '\0';
    char       *src_collversion = NULL;
    bool        src_istemplate;
    bool        src_allowconn;
    TransactionId src_frozenxid = InvalidTransactionId;
    MultiXactId src_minmxid = InvalidMultiXactId;
    Oid         src_deftablespace;
    volatile Oid dst_deftablespace;
    Relation    pg_database_rel;
    HeapTuple   tuple;
    Datum       new_record[Natts_pg_database] = {0};
    bool        new_record_nulls[Natts_pg_database] = {0};
    Oid         dboid = InvalidOid;
    Oid         datdba;
    ListCell   *option;
    DefElem    *dtablespacename = NULL;
    DefElem    *downer = NULL;
    DefElem    *dtemplate = NULL;
    DefElem    *dencoding = NULL;
    DefElem    *dlocale = NULL;
    DefElem    *dcollate = NULL;
    DefElem    *dctype = NULL;
    DefElem    *diculocale = NULL;
    DefElem    *dicurules = NULL;
    DefElem    *dlocprovider = NULL;
    DefElem    *distemplate = NULL;
    DefElem    *dallowconnections = NULL;
    DefElem    *dconnlimit = NULL;
    DefElem    *dcollversion = NULL;
    DefElem    *dstrategy = NULL;
    char       *dbname = stmt->dbname;
    char       *dbowner = NULL;
    const char *dbtemplate = NULL;
    char       *dbcollate = NULL;
    char       *dbctype = NULL;
    char       *dbiculocale = NULL;
    char       *dbicurules = NULL;
    char        dblocprovider = '\0';
    char       *canonname;
    int         encoding = -1;
    bool        dbistemplate = false;
    bool        dballowconnections = true;
    int         dbconnlimit = DATCONNLIMIT_UNLIMITED;
    char       *dbcollversion = NULL;
    int         notherbackends;
    int         npreparedxacts;
    CreateDBStrategy dbstrategy = CREATEDB_WAL_LOG;
    createdb_failure_params fparms;
 
    /* Extract options from the statement node tree */
    foreach(option, stmt->options)
    {
        DefElem    *defel = (DefElem *) lfirst(option);
 
        if (strcmp(defel->defname, "tablespace") == 0)
        {
            if (dtablespacename)
                errorConflictingDefElem(defel, pstate);
            dtablespacename = defel;
        }
        else if (strcmp(defel->defname, "owner") == 0)
        {
            if (downer)
                errorConflictingDefElem(defel, pstate);
            downer = defel;
        }
        else if (strcmp(defel->defname, "template") == 0)
        {
            if (dtemplate)
                errorConflictingDefElem(defel, pstate);
            dtemplate = defel;
        }
        else if (strcmp(defel->defname, "encoding") == 0)
        {
            if (dencoding)
                errorConflictingDefElem(defel, pstate);
            dencoding = defel;
        }
        else if (strcmp(defel->defname, "locale") == 0)
        {
            if (dlocale)
                errorConflictingDefElem(defel, pstate);
            dlocale = defel;
        }
        else if (strcmp(defel->defname, "lc_collate") == 0)
        {
            if (dcollate)
                errorConflictingDefElem(defel, pstate);
            dcollate = defel;
        }
        else if (strcmp(defel->defname, "lc_ctype") == 0)
        {
            if (dctype)
                errorConflictingDefElem(defel, pstate);
            dctype = defel;
        }
        else if (strcmp(defel->defname, "icu_locale") == 0)
        {
            if (diculocale)
                errorConflictingDefElem(defel, pstate);
            diculocale = defel;
        }
        else if (strcmp(defel->defname, "icu_rules") == 0)
        {
            if (dicurules)
                errorConflictingDefElem(defel, pstate);
            dicurules = defel;
        }
        else if (strcmp(defel->defname, "locale_provider") == 0)
        {
            if (dlocprovider)
                errorConflictingDefElem(defel, pstate);
            dlocprovider = defel;
        }
        else if (strcmp(defel->defname, "is_template") == 0)
        {
            if (distemplate)
                errorConflictingDefElem(defel, pstate);
            distemplate = defel;
        }
        else if (strcmp(defel->defname, "allow_connections") == 0)
        {
            if (dallowconnections)
                errorConflictingDefElem(defel, pstate);
            dallowconnections = defel;
        }
        else if (strcmp(defel->defname, "connection_limit") == 0)
        {
            if (dconnlimit)
                errorConflictingDefElem(defel, pstate);
            dconnlimit = defel;
        }
        else if (strcmp(defel->defname, "collation_version") == 0)
        {
            if (dcollversion)
                errorConflictingDefElem(defel, pstate);
            dcollversion = defel;
        }
        else if (strcmp(defel->defname, "location") == 0)
        {
            ereport(WARNING,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("LOCATION is not supported anymore"),
                     errhint("Consider using tablespaces instead."),
                     parser_errposition(pstate, defel->location)));
        }
        else if (strcmp(defel->defname, "oid") == 0)
        {
            dboid = defGetObjectId(defel);
 
            /*
             * We don't normally permit new databases to be created with
             * system-assigned OIDs. pg_upgrade tries to preserve database
             * OIDs, so we can't allow any database to be created with an OID
             * that might be in use in a freshly-initialized cluster created
             * by some future version. We assume all such OIDs will be from
             * the system-managed OID range.
             *
             * As an exception, however, we permit any OID to be assigned when
             * allow_system_table_mods=on (so that initdb can assign system
             * OIDs to template0 and postgres) or when performing a binary
             * upgrade (so that pg_upgrade can preserve whatever OIDs it finds
             * in the source cluster).
             */
            if (dboid < FirstNormalObjectId &&
                !allowSystemTableMods && !IsBinaryUpgrade)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE)),
                        errmsg("OIDs less than %u are reserved for system objects", FirstNormalObjectId));
        }
        else if (strcmp(defel->defname, "strategy") == 0)
        {
            if (dstrategy)
                errorConflictingDefElem(defel, pstate);
            dstrategy = defel;
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("option \"%s\" not recognized", defel->defname),
                     parser_errposition(pstate, defel->location)));
    }
 
    if (downer && downer->arg)
        dbowner = defGetString(downer);
    if (dtemplate && dtemplate->arg)
        dbtemplate = defGetString(dtemplate);
    if (dencoding && dencoding->arg)
    {
        const char *encoding_name;
 
        if (IsA(dencoding->arg, Integer))
        {
            encoding = defGetInt32(dencoding);
            encoding_name = pg_encoding_to_char(encoding);
            if (strcmp(encoding_name, "") == 0 ||
                pg_valid_server_encoding(encoding_name) < 0)
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("%d is not a valid encoding code",
                                encoding),
                         parser_errposition(pstate, dencoding->location)));
        }
        else
        {
            encoding_name = defGetString(dencoding);
            encoding = pg_valid_server_encoding(encoding_name);
            if (encoding < 0)
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("%s is not a valid encoding name",
                                encoding_name),
                         parser_errposition(pstate, dencoding->location)));
        }
    }
    if (dlocale && dlocale->arg)
    {
        dbcollate = defGetString(dlocale);
        dbctype = defGetString(dlocale);
    }
    if (dcollate && dcollate->arg)
        dbcollate = defGetString(dcollate);
    if (dctype && dctype->arg)
        dbctype = defGetString(dctype);
    if (diculocale && diculocale->arg)
        dbiculocale = defGetString(diculocale);
    if (dicurules && dicurules->arg)
        dbicurules = defGetString(dicurules);
    if (dlocprovider && dlocprovider->arg)
    {
        char       *locproviderstr = defGetString(dlocprovider);
 
        if (pg_strcasecmp(locproviderstr, "icu") == 0)
            dblocprovider = COLLPROVIDER_ICU;
        else if (pg_strcasecmp(locproviderstr, "libc") == 0)
            dblocprovider = COLLPROVIDER_LIBC;
        else
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("unrecognized locale provider: %s",
                            locproviderstr)));
    }
    if (distemplate && distemplate->arg)
        dbistemplate = defGetBoolean(distemplate);
    if (dallowconnections && dallowconnections->arg)
        dballowconnections = defGetBoolean(dallowconnections);
    if (dconnlimit && dconnlimit->arg)
    {
        dbconnlimit = defGetInt32(dconnlimit);
        if (dbconnlimit < DATCONNLIMIT_UNLIMITED)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid connection limit: %d", dbconnlimit)));
    }
    if (dcollversion)
        dbcollversion = defGetString(dcollversion);
 
    /* obtain OID of proposed owner */
    if (dbowner)
        datdba = get_role_oid(dbowner, false);
    else
        datdba = GetUserId();
 
    /*
     * To create a database, must have createdb privilege and must be able to
     * become the target role (this does not imply that the target role itself
     * must have createdb privilege).  The latter provision guards against
     * "giveaway" attacks.  Note that a superuser will always have both of
     * these privileges a fortiori.
     */
    if (!have_createdb_privilege())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied to create database")));
 
    check_can_set_role(GetUserId(), datdba);
 
    /*
     * Lookup database (template) to be cloned, and obtain share lock on it.
     * ShareLock allows two CREATE DATABASEs to work from the same template
     * concurrently, while ensuring no one is busy dropping it in parallel
     * (which would be Very Bad since we'd likely get an incomplete copy
     * without knowing it).  This also prevents any new connections from being
     * made to the source until we finish copying it, so we can be sure it
     * won't change underneath us.
     */
    if (!dbtemplate)
        dbtemplate = "template1";   /* Default template database name */
 
    if (!get_db_info(dbtemplate, ShareLock,
                     &src_dboid, &src_owner, &src_encoding,
                     &src_istemplate, &src_allowconn,
                     &src_frozenxid, &src_minmxid, &src_deftablespace,
                     &src_collate, &src_ctype, &src_iculocale, &src_icurules, &src_locprovider,
                     &src_collversion))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("template database \"%s\" does not exist",
                        dbtemplate)));
 
    /*
     * If the source database was in the process of being dropped, we can't
     * use it as a template.
     */
    if (database_is_invalid_oid(src_dboid))
        ereport(ERROR,
                errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                errmsg("cannot use invalid database \"%s\" as template", dbtemplate),
                errhint("Use DROP DATABASE to drop invalid databases."));
 
    /*
     * Permission check: to copy a DB that's not marked datistemplate, you
     * must be superuser or the owner thereof.
     */
    if (!src_istemplate)
    {
        if (!object_ownercheck(DatabaseRelationId, src_dboid, GetUserId()))
            ereport(ERROR,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission denied to copy database \"%s\"",
                            dbtemplate)));
    }
 
    /* Validate the database creation strategy. */
    if (dstrategy && dstrategy->arg)
    {
        char       *strategy;
 
        strategy = defGetString(dstrategy);
        if (strcmp(strategy, "wal_log") == 0)
            dbstrategy = CREATEDB_WAL_LOG;
        else if (strcmp(strategy, "file_copy") == 0)
            dbstrategy = CREATEDB_FILE_COPY;
        else
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid create database strategy \"%s\"", strategy),
                     errhint("Valid strategies are \"wal_log\", and \"file_copy\".")));
    }
 
    /* If encoding or locales are defaulted, use source's setting */
    if (encoding < 0)
        encoding = src_encoding;
    if (dbcollate == NULL)
        dbcollate = src_collate;
    if (dbctype == NULL)
        dbctype = src_ctype;
    if (dblocprovider == '\0')
        dblocprovider = src_locprovider;
    if (dbiculocale == NULL && dblocprovider == COLLPROVIDER_ICU)
    {
        if (dlocale && dlocale->arg)
            dbiculocale = defGetString(dlocale);
        else
            dbiculocale = src_iculocale;
    }
    if (dbicurules == NULL && dblocprovider == COLLPROVIDER_ICU)
        dbicurules = src_icurules;
 
    /* Some encodings are client only */
    if (!PG_VALID_BE_ENCODING(encoding))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("invalid server encoding %d", encoding)));
 
    /* Check that the chosen locales are valid, and get canonical spellings */
    if (!check_locale(LC_COLLATE, dbcollate, &canonname))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("invalid LC_COLLATE locale name: \"%s\"", dbcollate),
                 errhint("If the locale name is specific to ICU, use ICU_LOCALE.")));
    dbcollate = canonname;
    if (!check_locale(LC_CTYPE, dbctype, &canonname))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("invalid LC_CTYPE locale name: \"%s\"", dbctype),
                 errhint("If the locale name is specific to ICU, use ICU_LOCALE.")));
    dbctype = canonname;
 
    check_encoding_locale_matches(encoding, dbcollate, dbctype);
 
    if (dblocprovider == COLLPROVIDER_ICU)
    {
        if (!(is_encoding_supported_by_icu(encoding)))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("encoding \"%s\" is not supported with ICU provider",
                            pg_encoding_to_char(encoding))));
 
        /*
         * This would happen if template0 uses the libc provider but the new
         * database uses icu.
         */
        if (!dbiculocale)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("LOCALE or ICU_LOCALE must be specified")));
 
        /*
         * During binary upgrade, or when the locale came from the template
         * database, preserve locale string. Otherwise, canonicalize to a
         * language tag.
         */
        if (!IsBinaryUpgrade && dbiculocale != src_iculocale)
        {
            char       *langtag = icu_language_tag(dbiculocale,
                                                   icu_validation_level);
 
            if (langtag && strcmp(dbiculocale, langtag) != 0)
            {
                ereport(NOTICE,
                        (errmsg("using standard form \"%s\" for ICU locale \"%s\"",
                                langtag, dbiculocale)));
 
                dbiculocale = langtag;
            }
        }
 
        icu_validate_locale(dbiculocale);
    }
    else
    {
        if (dbiculocale)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("ICU locale cannot be specified unless locale provider is ICU")));
 
        if (dbicurules)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("ICU rules cannot be specified unless locale provider is ICU")));
    }
 
    /*
     * Check that the new encoding and locale settings match the source
     * database.  We insist on this because we simply copy the source data ---
     * any non-ASCII data would be wrongly encoded, and any indexes sorted
     * according to the source locale would be wrong.
     *
     * However, we assume that template0 doesn't contain any non-ASCII data
     * nor any indexes that depend on collation or ctype, so template0 can be
     * used as template for creating a database with any encoding or locale.
     */
    if (strcmp(dbtemplate, "template0") != 0)
    {
        if (encoding != src_encoding)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("new encoding (%s) is incompatible with the encoding of the template database (%s)",
                            pg_encoding_to_char(encoding),
                            pg_encoding_to_char(src_encoding)),
                     errhint("Use the same encoding as in the template database, or use template0 as template.")));
 
        if (strcmp(dbcollate, src_collate) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("new collation (%s) is incompatible with the collation of the template database (%s)",
                            dbcollate, src_collate),
                     errhint("Use the same collation as in the template database, or use template0 as template.")));
 
        if (strcmp(dbctype, src_ctype) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("new LC_CTYPE (%s) is incompatible with the LC_CTYPE of the template database (%s)",
                            dbctype, src_ctype),
                     errhint("Use the same LC_CTYPE as in the template database, or use template0 as template.")));
 
        if (dblocprovider != src_locprovider)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("new locale provider (%s) does not match locale provider of the template database (%s)",
                            collprovider_name(dblocprovider), collprovider_name(src_locprovider)),
                     errhint("Use the same locale provider as in the template database, or use template0 as template.")));
 
        if (dblocprovider == COLLPROVIDER_ICU)
        {
            char       *val1;
            char       *val2;
 
            Assert(dbiculocale);
            Assert(src_iculocale);
            if (strcmp(dbiculocale, src_iculocale) != 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("new ICU locale (%s) is incompatible with the ICU locale of the template database (%s)",
                                dbiculocale, src_iculocale),
                         errhint("Use the same ICU locale as in the template database, or use template0 as template.")));
 
            val1 = dbicurules;
            if (!val1)
                val1 = "";
            val2 = src_icurules;
            if (!val2)
                val2 = "";
            if (strcmp(val1, val2) != 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("new ICU collation rules (%s) are incompatible with the ICU collation rules of the template database (%s)",
                                val1, val2),
                         errhint("Use the same ICU collation rules as in the template database, or use template0 as template.")));
        }
    }
 
    /*
     * If we got a collation version for the template database, check that it
     * matches the actual OS collation version.  Otherwise error; the user
     * needs to fix the template database first.  Don't complain if a
     * collation version was specified explicitly as a statement option; that
     * is used by pg_upgrade to reproduce the old state exactly.
     *
     * (If the template database has no collation version, then either the
     * platform/provider does not support collation versioning, or it's
     * template0, for which we stipulate that it does not contain
     * collation-using objects.)
     */
    if (src_collversion && !dcollversion)
    {
        char       *actual_versionstr;
 
        actual_versionstr = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);
        if (!actual_versionstr)
            ereport(ERROR,
                    (errmsg("template database \"%s\" has a collation version, but no actual collation version could be determined",
                            dbtemplate)));
 
        if (strcmp(actual_versionstr, src_collversion) != 0)
            ereport(ERROR,
                    (errmsg("template database \"%s\" has a collation version mismatch",
                            dbtemplate),
                     errdetail("The template database was created using collation version %s, "
                               "but the operating system provides version %s.",
                               src_collversion, actual_versionstr),
                     errhint("Rebuild all objects in the template database that use the default collation and run "
                             "ALTER DATABASE %s REFRESH COLLATION VERSION, "
                             "or build PostgreSQL with the right library version.",
                             quote_identifier(dbtemplate))));
    }
 
    if (dbcollversion == NULL)
        dbcollversion = src_collversion;
 
    /*
     * Normally, we copy the collation version from the template database.
     * This last resort only applies if the template database does not have a
     * collation version, which is normally only the case for template0.
     */
    if (dbcollversion == NULL)
        dbcollversion = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);
 
    /* Resolve default tablespace for new database */
    if (dtablespacename && dtablespacename->arg)
    {
        char       *tablespacename;
        AclResult   aclresult;
 
        tablespacename = defGetString(dtablespacename);
        dst_deftablespace = get_tablespace_oid(tablespacename, false);
        /* check permissions */
        aclresult = object_aclcheck(TableSpaceRelationId, dst_deftablespace, GetUserId(),
                                    ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, OBJECT_TABLESPACE,
                           tablespacename);
 
        /* pg_global must never be the default tablespace */
        if (dst_deftablespace == GLOBALTABLESPACE_OID)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("pg_global cannot be used as default tablespace")));
 
        /*
         * If we are trying to change the default tablespace of the template,
         * we require that the template not have any files in the new default
         * tablespace.  This is necessary because otherwise the copied
         * database would contain pg_class rows that refer to its default
         * tablespace both explicitly (by OID) and implicitly (as zero), which
         * would cause problems.  For example another CREATE DATABASE using
         * the copied database as template, and trying to change its default
         * tablespace again, would yield outright incorrect results (it would
         * improperly move tables to the new default tablespace that should
         * stay in the same tablespace).
         */
        if (dst_deftablespace != src_deftablespace)
        {
            char       *srcpath;
            struct stat st;
 
            srcpath = GetDatabasePath(src_dboid, dst_deftablespace);
 
            if (stat(srcpath, &st) == 0 &&
                S_ISDIR(st.st_mode) &&
                !directory_is_empty(srcpath))
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot assign new default tablespace \"%s\"",
                                tablespacename),
                         errdetail("There is a conflict because database \"%s\" already has some tables in this tablespace.",
                                   dbtemplate)));
            pfree(srcpath);
        }
    }
    else
    {
        /* Use template database's default tablespace */
        dst_deftablespace = src_deftablespace;
        /* Note there is no additional permission check in this path */
    }
 
    /*
     * If built with appropriate switch, whine when regression-testing
     * conventions for database names are violated.  But don't complain during
     * initdb.
     */
#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
    if (IsUnderPostmaster && strstr(dbname, "regression") == NULL)
        elog(WARNING, "databases created by regression test cases should have names including \"regression\"");
#endif
 
    /*
     * Check for db name conflict.  This is just to give a more friendly error
     * message than "unique index violation".  There's a race condition but
     * we're willing to accept the less friendly message in that case.
     */
    if (OidIsValid(get_database_oid(dbname, true)))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_DATABASE),
                 errmsg("database \"%s\" already exists", dbname)));
 
    /*
     * The source DB can't have any active backends, except this one
     * (exception is to allow CREATE DB while connected to template1).
     * Otherwise we might copy inconsistent data.
     *
     * This should be last among the basic error checks, because it involves
     * potential waiting; we may as well throw an error first if we're gonna
     * throw one.
     */
    if (CountOtherDBBackends(src_dboid, &notherbackends, &npreparedxacts))
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("source database \"%s\" is being accessed by other users",
                        dbtemplate),
                 errdetail_busy_db(notherbackends, npreparedxacts)));
 
    /*
     * Select an OID for the new database, checking that it doesn't have a
     * filename conflict with anything already existing in the tablespace
     * directories.
     */
    pg_database_rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
    /*
     * If database OID is configured, check if the OID is already in use or
     * data directory already exists.
     */
    if (OidIsValid(dboid))
    {
        char       *existing_dbname = get_database_name(dboid);
 
        if (existing_dbname != NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE)),
                    errmsg("database OID %u is already in use by database \"%s\"",
                           dboid, existing_dbname));
 
        if (check_db_file_conflict(dboid))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE)),
                    errmsg("data directory with the specified OID %u already exists", dboid));
    }
    else
    {
        /* Select an OID for the new database if is not explicitly configured. */
        do
        {
            dboid = GetNewOidWithIndex(pg_database_rel, DatabaseOidIndexId,
                                       Anum_pg_database_oid);
        } while (check_db_file_conflict(dboid));
    }
 
    /*
     * Insert a new tuple into pg_database.  This establishes our ownership of
     * the new database name (anyone else trying to insert the same name will
     * block on the unique index, and fail after we commit).
     */
 
    Assert((dblocprovider == COLLPROVIDER_ICU && dbiculocale) ||
           (dblocprovider != COLLPROVIDER_ICU && !dbiculocale));
 
    /* Form tuple */
    new_record[Anum_pg_database_oid - 1] = ObjectIdGetDatum(dboid);
    new_record[Anum_pg_database_datname - 1] =
        DirectFunctionCall1(namein, CStringGetDatum(dbname));
    new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);
    new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);
    new_record[Anum_pg_database_datlocprovider - 1] = CharGetDatum(dblocprovider);
    new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
    new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
    new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
    new_record[Anum_pg_database_datfrozenxid - 1] = TransactionIdGetDatum(src_frozenxid);
    new_record[Anum_pg_database_datminmxid - 1] = TransactionIdGetDatum(src_minmxid);
    new_record[Anum_pg_database_dattablespace - 1] = ObjectIdGetDatum(dst_deftablespace);
    new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);
    new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);
    if (dbiculocale)
        new_record[Anum_pg_database_daticulocale - 1] = CStringGetTextDatum(dbiculocale);
    else
        new_record_nulls[Anum_pg_database_daticulocale - 1] = true;
    if (dbicurules)
        new_record[Anum_pg_database_daticurules - 1] = CStringGetTextDatum(dbicurules);
    else
        new_record_nulls[Anum_pg_database_daticurules - 1] = true;
    if (dbcollversion)
        new_record[Anum_pg_database_datcollversion - 1] = CStringGetTextDatum(dbcollversion);
    else
        new_record_nulls[Anum_pg_database_datcollversion - 1] = true;
 
    /*
     * We deliberately set datacl to default (NULL), rather than copying it
     * from the template database.  Copying it would be a bad idea when the
     * owner is not the same as the template's owner.
     */
    new_record_nulls[Anum_pg_database_datacl - 1] = true;
 
    tuple = heap_form_tuple(RelationGetDescr(pg_database_rel),
                            new_record, new_record_nulls);
 
    CatalogTupleInsert(pg_database_rel, tuple);
 
    /*
     * Now generate additional catalog entries associated with the new DB
     */
 
    /* Register owner dependency */
    recordDependencyOnOwner(DatabaseRelationId, dboid, datdba);
 
    /* Create pg_shdepend entries for objects within database */
    copyTemplateDependencies(src_dboid, dboid);
 
    /* Post creation hook for new database */
    InvokeObjectPostCreateHook(DatabaseRelationId, dboid, 0);
 
    /*
     * If we're going to be reading data for the to-be-created database into
     * shared_buffers, take a lock on it. Nobody should know that this
     * database exists yet, but it's good to maintain the invariant that an
     * AccessExclusiveLock on the database is sufficient to drop all of its
     * buffers without worrying about more being read later.
     *
     * Note that we need to do this before entering the
     * PG_ENSURE_ERROR_CLEANUP block below, because createdb_failure_callback
     * expects this lock to be held already.
     */
    if (dbstrategy == CREATEDB_WAL_LOG)
        LockSharedObject(DatabaseRelationId, dboid, 0, AccessShareLock);
 
    /*
     * Once we start copying subdirectories, we need to be able to clean 'em
     * up if we fail.  Use an ENSURE block to make sure this happens.  (This
     * is not a 100% solution, because of the possibility of failure during
     * transaction commit after we leave this routine, but it should handle
     * most scenarios.)
     */
    fparms.src_dboid = src_dboid;
    fparms.dest_dboid = dboid;
    fparms.strategy = dbstrategy;
 
    PG_ENSURE_ERROR_CLEANUP(createdb_failure_callback,
                            PointerGetDatum(&fparms));
    {
        /*
         * If the user has asked to create a database with WAL_LOG strategy
         * then call CreateDatabaseUsingWalLog, which will copy the database
         * at the block level and it will WAL log each copied block.
         * Otherwise, call CreateDatabaseUsingFileCopy that will copy the
         * database file by file.
         */
        if (dbstrategy == CREATEDB_WAL_LOG)
            CreateDatabaseUsingWalLog(src_dboid, dboid, src_deftablespace,
                                      dst_deftablespace);
        else
            CreateDatabaseUsingFileCopy(src_dboid, dboid, src_deftablespace,
                                        dst_deftablespace);
 
        /*
         * Close pg_database, but keep lock till commit.
         */
        table_close(pg_database_rel, NoLock);
 
        /*
         * Force synchronous commit, thus minimizing the window between
         * creation of the database files and committal of the transaction. If
         * we crash before committing, we'll have a DB that's taking up disk
         * space but is not in pg_database, which is not good.
         */
        ForceSyncCommit();
    }
    PG_END_ENSURE_ERROR_CLEANUP(createdb_failure_callback,
                                PointerGetDatum(&fparms));
 
    return dboid;
}
 
/*
 * Check whether chosen encoding matches chosen locale settings.  This
 * restriction is necessary because libc's locale-specific code usually
 * fails when presented with data in an encoding it's not expecting. We
 * allow mismatch in four cases:
 *
 * 1. locale encoding = SQL_ASCII, which means that the locale is C/POSIX
 * which works with any encoding.
 *
 * 2. locale encoding = -1, which means that we couldn't determine the
 * locale's encoding and have to trust the user to get it right.
 *
 * 3. selected encoding is UTF8 and platform is win32. This is because
 * UTF8 is a pseudo codepage that is supported in all locales since it's
 * converted to UTF16 before being used.
 *
 * 4. selected encoding is SQL_ASCII, but only if you're a superuser. This
 * is risky but we have historically allowed it --- notably, the
 * regression tests require it.
 *
 * Note: if you change this policy, fix initdb to match.
 */
void
check_encoding_locale_matches(int encoding, const char *collate, const char *ctype)
{
    int         ctype_encoding = pg_get_encoding_from_locale(ctype, true);
    int         collate_encoding = pg_get_encoding_from_locale(collate, true);
 
    if (!(ctype_encoding == encoding ||
          ctype_encoding == PG_SQL_ASCII ||
          ctype_encoding == -1 ||
#ifdef WIN32
          encoding == PG_UTF8 ||
#endif
          (encoding == PG_SQL_ASCII && superuser())))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("encoding \"%s\" does not match locale \"%s\"",
                        pg_encoding_to_char(encoding),
                        ctype),
                 errdetail("The chosen LC_CTYPE setting requires encoding \"%s\".",
                           pg_encoding_to_char(ctype_encoding))));
 
    if (!(collate_encoding == encoding ||
          collate_encoding == PG_SQL_ASCII ||
          collate_encoding == -1 ||
#ifdef WIN32
          encoding == PG_UTF8 ||
#endif
          (encoding == PG_SQL_ASCII && superuser())))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("encoding \"%s\" does not match locale \"%s\"",
                        pg_encoding_to_char(encoding),
                        collate),
                 errdetail("The chosen LC_COLLATE setting requires encoding \"%s\".",
                           pg_encoding_to_char(collate_encoding))));
}
 
/* Error cleanup callback for createdb */
static void
createdb_failure_callback(int code, Datum arg)
{
    createdb_failure_params *fparms = (createdb_failure_params *) DatumGetPointer(arg);
 
    /*
     * If we were copying database at block levels then drop pages for the
     * destination database that are in the shared buffer cache.  And tell
     * checkpointer to forget any pending fsync and unlink requests for files
     * in the database.  The reasoning behind doing this is same as explained
     * in dropdb function.  But unlike dropdb we don't need to call
     * pgstat_drop_database because this database is still not created so
     * there should not be any stat for this.
     */
    if (fparms->strategy == CREATEDB_WAL_LOG)
    {
        DropDatabaseBuffers(fparms->dest_dboid);
        ForgetDatabaseSyncRequests(fparms->dest_dboid);
 
        /* Release lock on the target database. */
        UnlockSharedObject(DatabaseRelationId, fparms->dest_dboid, 0,
                           AccessShareLock);
    }
 
    /*
     * Release lock on source database before doing recursive remove. This is
     * not essential but it seems desirable to release the lock as soon as
     * possible.
     */
    UnlockSharedObject(DatabaseRelationId, fparms->src_dboid, 0, ShareLock);
 
    /* Throw away any successfully copied subdirectories */
    remove_dbtablespaces(fparms->dest_dboid);
}
 
 
/*
 * DROP DATABASE
 */
void
dropdb(const char *dbname, bool missing_ok, bool force)
{
    Oid         db_id;
    bool        db_istemplate;
    Relation    pgdbrel;
    HeapTuple   tup;
    Form_pg_database datform;
    int         notherbackends;
    int         npreparedxacts;
    int         nslots,
                nslots_active;
    int         nsubscriptions;
 
    /*
     * Look up the target database's OID, and get exclusive lock on it. We
     * need this to ensure that no new backend starts up in the target
     * database while we are deleting it (see postinit.c), and that no one is
     * using it as a CREATE DATABASE template or trying to delete it for
     * themselves.
     */
    pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
    if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
                     &db_istemplate, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
    {
        if (!missing_ok)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_DATABASE),
                     errmsg("database \"%s\" does not exist", dbname)));
        }
        else
        {
            /* Close pg_database, release the lock, since we changed nothing */
            table_close(pgdbrel, RowExclusiveLock);
            ereport(NOTICE,
                    (errmsg("database \"%s\" does not exist, skipping",
                            dbname)));
            return;
        }
    }
 
    /*
     * Permission checks
     */
    if (!object_ownercheck(DatabaseRelationId, db_id, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                       dbname);
 
    /* DROP hook for the database being removed */
    InvokeObjectDropHook(DatabaseRelationId, db_id, 0);
 
    /*
     * Disallow dropping a DB that is marked istemplate.  This is just to
     * prevent people from accidentally dropping template0 or template1; they
     * can do so if they're really determined ...
     */
    if (db_istemplate)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot drop a template database")));
 
    /* Obviously can't drop my own database */
    if (db_id == MyDatabaseId)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("cannot drop the currently open database")));
 
    /*
     * Check whether there are active logical slots that refer to the
     * to-be-dropped database. The database lock we are holding prevents the
     * creation of new slots using the database or existing slots becoming
     * active.
     */
    (void) ReplicationSlotsCountDBSlots(db_id, &nslots, &nslots_active);
    if (nslots_active)
    {
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("database \"%s\" is used by an active logical replication slot",
                        dbname),
                 errdetail_plural("There is %d active slot.",
                                  "There are %d active slots.",
                                  nslots_active, nslots_active)));
    }
 
    /*
     * Check if there are subscriptions defined in the target database.
     *
     * We can't drop them automatically because they might be holding
     * resources in other databases/instances.
     */
    if ((nsubscriptions = CountDBSubscriptions(db_id)) > 0)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("database \"%s\" is being used by logical replication subscription",
                        dbname),
                 errdetail_plural("There is %d subscription.",
                                  "There are %d subscriptions.",
                                  nsubscriptions, nsubscriptions)));
 
 
    /*
     * Attempt to terminate all existing connections to the target database if
     * the user has requested to do so.
     */
    if (force)
        TerminateOtherDBBackends(db_id);
 
    /*
     * Check for other backends in the target database.  (Because we hold the
     * database lock, no new ones can start after this.)
     *
     * As in CREATE DATABASE, check this after other error conditions.
     */
    if (CountOtherDBBackends(db_id, &notherbackends, &npreparedxacts))
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("database \"%s\" is being accessed by other users",
                        dbname),
                 errdetail_busy_db(notherbackends, npreparedxacts)));
 
    /*
     * Delete any comments or security labels associated with the database.
     */
    DeleteSharedComments(db_id, DatabaseRelationId);
    DeleteSharedSecurityLabel(db_id, DatabaseRelationId);
 
    /*
     * Remove settings associated with this database
     */
    DropSetting(db_id, InvalidOid);
 
    /*
     * Remove shared dependency references for the database.
     */
    dropDatabaseDependencies(db_id);
 
    /*
     * Tell the cumulative stats system to forget it immediately, too.
     */
    pgstat_drop_database(db_id);
 
    tup = SearchSysCacheCopy1(DATABASEOID, ObjectIdGetDatum(db_id));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for database %u", db_id);
    datform = (Form_pg_database) GETSTRUCT(tup);
 
    /*
     * Except for the deletion of the catalog row, subsequent actions are not
     * transactional (consider DropDatabaseBuffers() discarding modified
     * buffers). But we might crash or get interrupted below. To prevent
     * accesses to a database with invalid contents, mark the database as
     * invalid using an in-place update.
     *
     * We need to flush the WAL before continuing, to guarantee the
     * modification is durable before performing irreversible filesystem
     * operations.
     */
    datform->datconnlimit = DATCONNLIMIT_INVALID_DB;
    heap_inplace_update(pgdbrel, tup);
    XLogFlush(XactLastRecEnd);
 
    /*
     * Also delete the tuple - transactionally. If this transaction commits,
     * the row will be gone, but if we fail, dropdb() can be invoked again.
     */
    CatalogTupleDelete(pgdbrel, &tup->t_self);
 
    /*
     * Drop db-specific replication slots.
     */
    ReplicationSlotsDropDBSlots(db_id);
 
    /*
     * Drop pages for this database that are in the shared buffer cache. This
     * is important to ensure that no remaining backend tries to write out a
     * dirty buffer to the dead database later...
     */
    DropDatabaseBuffers(db_id);
 
    /*
     * Tell checkpointer to forget any pending fsync and unlink requests for
     * files in the database; else the fsyncs will fail at next checkpoint, or
     * worse, it will delete files that belong to a newly created database
     * with the same OID.
     */
    ForgetDatabaseSyncRequests(db_id);
 
    /*
     * Force a checkpoint to make sure the checkpointer has received the
     * message sent by ForgetDatabaseSyncRequests.
     */
    RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
 
    /* Close all smgr fds in all backends. */
    WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
 
    /*
     * Remove all tablespace subdirs belonging to the database.
     */
    remove_dbtablespaces(db_id);
 
    /*
     * Close pg_database, but keep lock till commit.
     */
    table_close(pgdbrel, NoLock);
 
    /*
     * Force synchronous commit, thus minimizing the window between removal of
     * the database files and committal of the transaction. If we crash before
     * committing, we'll have a DB that's gone on disk but still there
     * according to pg_database, which is not good.
     */
    ForceSyncCommit();
}
 
 
/*
 * Rename database
 */
ObjectAddress
RenameDatabase(const char *oldname, const char *newname)
{
    Oid         db_id;
    HeapTuple   newtup;
    Relation    rel;
    int         notherbackends;
    int         npreparedxacts;
    ObjectAddress address;
 
    /*
     * Look up the target database's OID, and get exclusive lock on it. We
     * need this for the same reasons as DROP DATABASE.
     */
    rel = table_open(DatabaseRelationId, RowExclusiveLock);
 
    if (!get_db_info(oldname, AccessExclusiveLock, &db_id, NULL, NULL,
                     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" does not exist", oldname)));
 
    /* must be owner */
    if (!object_ownercheck(DatabaseRelationId, db_id, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                       oldname);
 
    /* must have createdb rights */
    if (!have_createdb_privilege())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied to rename database")));
 
    /*
     * If built with appropriate switch, whine when regression-testing
     * conventions for database names are violated.
     */
#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
    if (strstr(newname, "regression") == NULL)
        elog(WARNING, "databases created by regression test cases should have names including \"regression\"");
#endif
 
    /*
     * Make sure the new name doesn't exist.  See notes for same error in
     * CREATE DATABASE.
     */
    if (OidIsValid(get_database_oid(newname, true)))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_DATABASE),
                 errmsg("database \"%s\" already exists", newname)));
 
    /*
     * XXX Client applications probably store the current database somewhere,
     * so renaming it could cause confusion.  On the other hand, there may not
     * be an actual problem besides a little confusion, so think about this
     * and decide.
     */
    if (db_id == MyDatabaseId)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("current database cannot be renamed")));
 
    /*
     * Make sure the database does not have active sessions.  This is the same
     * concern as above, but applied to other sessions.
     *
     * As in CREATE DATABASE, check this after other error conditions.
     */
    if (CountOtherDBBackends(db_id, &notherbackends, &npreparedxacts))
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("database \"%s\" is being accessed by other users",
                        oldname),
                 errdetail_busy_db(notherbackends, npreparedxacts)));
 
    /* rename */
    newtup = SearchSysCacheCopy1(DATABASEOID, ObjectIdGetDatum(db_id));
    if (!HeapTupleIsValid(newtup))
        elog(ERROR, "cache lookup failed for database %u", db_id);
    namestrcpy(&(((Form_pg_database) GETSTRUCT(newtup))->datname), newname);
    CatalogTupleUpdate(rel, &newtup->t_self, newtup);
 
    InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
 
    ObjectAddressSet(address, DatabaseRelationId, db_id);
 
    /*
     * Close pg_database, but keep lock till commit.
     */
    table_close(rel, NoLock);
 
    return address;
}
 
 
/*
 * ALTER DATABASE SET TABLESPACE
 */
static void
movedb(const char *dbname, const char *tblspcname)
{
    Oid         db_id;
    Relation    pgdbrel;
    int         notherbackends;
    int         npreparedxacts;
    HeapTuple   oldtuple,
                newtuple;
    Oid         src_tblspcoid,
                dst_tblspcoid;
    ScanKeyData scankey;
    SysScanDesc sysscan;
    AclResult   aclresult;
    char       *src_dbpath;
    char       *dst_dbpath;
    DIR        *dstdir;
    struct dirent *xlde;
    movedb_failure_params fparms;
 
    /*
     * Look up the target database's OID, and get exclusive lock on it. We
     * need this to ensure that no new backend starts up in the database while
     * we are moving it, and that no one is using it as a CREATE DATABASE
     * template or trying to delete it.
     */
    pgdbrel = table_open(DatabaseRelationId, RowExclusiveLock);
 
    if (!get_db_info(dbname, AccessExclusiveLock, &db_id, NULL, NULL,
                     NULL, NULL, NULL, NULL, &src_tblspcoid, NULL, NULL, NULL, NULL, NULL, NULL))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" does not exist", dbname)));
 
    /*
     * We actually need a session lock, so that the lock will persist across
     * the commit/restart below.  (We could almost get away with letting the
     * lock be released at commit, except that someone could try to move
     * relations of the DB back into the old directory while we rmtree() it.)
     */
    LockSharedObjectForSession(DatabaseRelationId, db_id, 0,
                               AccessExclusiveLock);
 
    /*
     * Permission checks
     */
    if (!object_ownercheck(DatabaseRelationId, db_id, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                       dbname);
 
    /*
     * Obviously can't move the tables of my own database
     */
    if (db_id == MyDatabaseId)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("cannot change the tablespace of the currently open database")));
 
    /*
     * Get tablespace's oid
     */
    dst_tblspcoid = get_tablespace_oid(tblspcname, false);
 
    /*
     * Permission checks
     */
    aclresult = object_aclcheck(TableSpaceRelationId, dst_tblspcoid, GetUserId(),
                                ACL_CREATE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, OBJECT_TABLESPACE,
                       tblspcname);
 
    /*
     * pg_global must never be the default tablespace
     */
    if (dst_tblspcoid == GLOBALTABLESPACE_OID)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("pg_global cannot be used as default tablespace")));
 
    /*
     * No-op if same tablespace
     */
    if (src_tblspcoid == dst_tblspcoid)
    {
        table_close(pgdbrel, NoLock);
        UnlockSharedObjectForSession(DatabaseRelationId, db_id, 0,
                                     AccessExclusiveLock);
        return;
    }
 
    /*
     * Check for other backends in the target database.  (Because we hold the
     * database lock, no new ones can start after this.)
     *
     * As in CREATE DATABASE, check this after other error conditions.
     */
    if (CountOtherDBBackends(db_id, &notherbackends, &npreparedxacts))
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("database \"%s\" is being accessed by other users",
                        dbname),
                 errdetail_busy_db(notherbackends, npreparedxacts)));
 
    /*
     * Get old and new database paths
     */
    src_dbpath = GetDatabasePath(db_id, src_tblspcoid);
    dst_dbpath = GetDatabasePath(db_id, dst_tblspcoid);
 
    /*
     * Force a checkpoint before proceeding. This will force all dirty
     * buffers, including those of unlogged tables, out to disk, to ensure
     * source database is up-to-date on disk for the copy.
     * FlushDatabaseBuffers() would suffice for that, but we also want to
     * process any pending unlink requests. Otherwise, the check for existing
     * files in the target directory might fail unnecessarily, not to mention
     * that the copy might fail due to source files getting deleted under it.
     * On Windows, this also ensures that background procs don't hold any open
     * files, which would cause rmdir() to fail.
     */
    RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT
                      | CHECKPOINT_FLUSH_ALL);
 
    /* Close all smgr fds in all backends. */
    WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
 
    /*
     * Now drop all buffers holding data of the target database; they should
     * no longer be dirty so DropDatabaseBuffers is safe.
     *
     * It might seem that we could just let these buffers age out of shared
     * buffers naturally, since they should not get referenced anymore.  The
     * problem with that is that if the user later moves the database back to
     * its original tablespace, any still-surviving buffers would appear to
     * contain valid data again --- but they'd be missing any changes made in
     * the database while it was in the new tablespace.  In any case, freeing
     * buffers that should never be used again seems worth the cycles.
     *
     * Note: it'd be sufficient to get rid of buffers matching db_id and
     * src_tblspcoid, but bufmgr.c presently provides no API for that.
     */
    DropDatabaseBuffers(db_id);
 
    /*
     * Check for existence of files in the target directory, i.e., objects of
     * this database that are already in the target tablespace.  We can't
     * allow the move in such a case, because we would need to change those
     * relations' pg_class.reltablespace entries to zero, and we don't have
     * access to the DB's pg_class to do so.
     */
    dstdir = AllocateDir(dst_dbpath);
    if (dstdir != NULL)
    {
        while ((xlde = ReadDir(dstdir, dst_dbpath)) != NULL)
        {
            if (strcmp(xlde->d_name, ".") == 0 ||
                strcmp(xlde->d_name, "..") == 0)
                continue;
 
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("some relations of database \"%s\" are already in tablespace \"%s\"",
                            dbname, tblspcname),
                     errhint("You must move them back to the database's default tablespace before using this command.")));
        }
 
        FreeDir(dstdir);
 
        /*
         * The directory exists but is empty. We must remove it before using
         * the copydir function.
         */
        if (rmdir(dst_dbpath) != 0)
            elog(ERROR, "could not remove directory \"%s\": %m",
                 dst_dbpath);
    }
 
    /*
     * Use an ENSURE block to make sure we remove the debris if the copy fails
     * (eg, due to out-of-disk-space).  This is not a 100% solution, because
     * of the possibility of failure during transaction commit, but it should
     * handle most scenarios.
     */
    fparms.dest_dboid = db_id;
    fparms.dest_tsoid = dst_tblspcoid;
    PG_ENSURE_ERROR_CLEANUP(movedb_failure_callback,
                            PointerGetDatum(&fparms));
    {
        Datum       new_record[Natts_pg_database] = {0};
        bool        new_record_nulls[Natts_pg_database] = {0};
        bool        new_record_repl[Natts_pg_database] = {0};
 
        /*
         * Copy files from the old tablespace to the new one
         */
        copydir(src_dbpath, dst_dbpath, false);
 
        /*
         * Record the filesystem change in XLOG
         */
        {
            xl_dbase_create_file_copy_rec xlrec;
 
            xlrec.db_id = db_id;
            xlrec.tablespace_id = dst_tblspcoid;
            xlrec.src_db_id = db_id;
            xlrec.src_tablespace_id = src_tblspcoid;
 
            XLogBeginInsert();
            XLogRegisterData((char *) &xlrec,
                             sizeof(xl_dbase_create_file_copy_rec));
 
            (void) XLogInsert(RM_DBASE_ID,
                              XLOG_DBASE_CREATE_FILE_COPY | XLR_SPECIAL_REL_UPDATE);
        }
 
        /*
         * Update the database's pg_database tuple
         */
        ScanKeyInit(&scankey,
                    Anum_pg_database_datname,
                    BTEqualStrategyNumber, F_NAMEEQ,
                    CStringGetDatum(dbname));
        sysscan = systable_beginscan(pgdbrel, DatabaseNameIndexId, true,
                                     NULL, 1, &scankey);
        oldtuple = systable_getnext(sysscan);
        if (!HeapTupleIsValid(oldtuple))    /* shouldn't happen... */
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_DATABASE),
                     errmsg("database \"%s\" does not exist", dbname)));
 
        new_record[Anum_pg_database_dattablespace - 1] = ObjectIdGetDatum(dst_tblspcoid);
        new_record_repl[Anum_pg_database_dattablespace - 1] = true;
 
        newtuple = heap_modify_tuple(oldtuple, RelationGetDescr(pgdbrel),
                                     new_record,
                                     new_record_nulls, new_record_repl);
        CatalogTupleUpdate(pgdbrel, &oldtuple->t_self, newtuple);
 
        InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
 
        systable_endscan(sysscan);
 
        /*
         * Force another checkpoint here.  As in CREATE DATABASE, this is to
         * ensure that we don't have to replay a committed
         * XLOG_DBASE_CREATE_FILE_COPY operation, which would cause us to lose
         * any unlogged operations done in the new DB tablespace before the
         * next checkpoint.
         */
        RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
 
        /*
         * Force synchronous commit, thus minimizing the window between
         * copying the database files and committal of the transaction. If we
         * crash before committing, we'll leave an orphaned set of files on
         * disk, which is not fatal but not good either.
         */
        ForceSyncCommit();
 
        /*
         * Close pg_database, but keep lock till commit.
         */
        table_close(pgdbrel, NoLock);
    }
    PG_END_ENSURE_ERROR_CLEANUP(movedb_failure_callback,
                                PointerGetDatum(&fparms));
 
    /*
     * Commit the transaction so that the pg_database update is committed. If
     * we crash while removing files, the database won't be corrupt, we'll
     * just leave some orphaned files in the old directory.
     *
     * (This is OK because we know we aren't inside a transaction block.)
     *
     * XXX would it be safe/better to do this inside the ensure block?  Not
     * convinced it's a good idea; consider elog just after the transaction
     * really commits.
     */
    PopActiveSnapshot();
    CommitTransactionCommand();
 
    /* Start new transaction for the remaining work; don't need a snapshot */
    StartTransactionCommand();
 
    /*
     * Remove files from the old tablespace
     */
    if (!rmtree(src_dbpath, true))
        ereport(WARNING,
                (errmsg("some useless files may be left behind in old database directory \"%s\"",
                        src_dbpath)));
 
    /*
     * Record the filesystem change in XLOG
     */
    {
        xl_dbase_drop_rec xlrec;
 
        xlrec.db_id = db_id;
        xlrec.ntablespaces = 1;
 
        XLogBeginInsert();
        XLogRegisterData((char *) &xlrec, sizeof(xl_dbase_drop_rec));
        XLogRegisterData((char *) &src_tblspcoid, sizeof(Oid));
 
        (void) XLogInsert(RM_DBASE_ID,
                          XLOG_DBASE_DROP | XLR_SPECIAL_REL_UPDATE);
    }
 
    /* Now it's safe to release the database lock */
    UnlockSharedObjectForSession(DatabaseRelationId, db_id, 0,
                                 AccessExclusiveLock);
 
    pfree(src_dbpath);
    pfree(dst_dbpath);
}
 
/* Error cleanup callback for movedb */
static void
movedb_failure_callback(int code, Datum arg)
{
    movedb_failure_params *fparms = (movedb_failure_params *) DatumGetPointer(arg);
    char       *dstpath;
 
    /* Get rid of anything we managed to copy to the target directory */
    dstpath = GetDatabasePath(fparms->dest_dboid, fparms->dest_tsoid);
 
    (void) rmtree(dstpath, true);
 
    pfree(dstpath);
}
 
/*
 * Process options and call dropdb function.
 */
void
DropDatabase(ParseState *pstate, DropdbStmt *stmt)
{
    bool        force = false;
    ListCell   *lc;
 
    foreach(lc, stmt->options)
    {
        DefElem    *opt = (DefElem *) lfirst(lc);
 
        if (strcmp(opt->defname, "force") == 0)
            force = true;
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("unrecognized DROP DATABASE option \"%s\"", opt->defname),
                     parser_errposition(pstate, opt->location)));
    }
 
    dropdb(stmt->dbname, stmt->missing_ok, force);
}
 
/*
 * ALTER DATABASE name ...
 */
Oid
AlterDatabase(ParseState *pstate, AlterDatabaseStmt *stmt, bool isTopLevel)
{
    Relation    rel;
    Oid         dboid;
    HeapTuple   tuple,
                newtuple;
    Form_pg_database datform;
    ScanKeyData scankey;
    SysScanDesc scan;
    ListCell   *option;
    bool        dbistemplate = false;
    bool        dballowconnections = true;
    int         dbconnlimit = DATCONNLIMIT_UNLIMITED;
    DefElem    *distemplate = NULL;
    DefElem    *dallowconnections = NULL;
    DefElem    *dconnlimit = NULL;
    DefElem    *dtablespace = NULL;
    Datum       new_record[Natts_pg_database] = {0};
    bool        new_record_nulls[Natts_pg_database] = {0};
    bool        new_record_repl[Natts_pg_database] = {0};
 
    /* Extract options from the statement node tree */
    foreach(option, stmt->options)
    {
        DefElem    *defel = (DefElem *) lfirst(option);
 
        if (strcmp(defel->defname, "is_template") == 0)
        {
            if (distemplate)
                errorConflictingDefElem(defel, pstate);
            distemplate = defel;
        }
        else if (strcmp(defel->defname, "allow_connections") == 0)
        {
            if (dallowconnections)
                errorConflictingDefElem(defel, pstate);
            dallowconnections = defel;
        }
        else if (strcmp(defel->defname, "connection_limit") == 0)
        {
            if (dconnlimit)
                errorConflictingDefElem(defel, pstate);
            dconnlimit = defel;
        }
        else if (strcmp(defel->defname, "tablespace") == 0)
        {
            if (dtablespace)
                errorConflictingDefElem(defel, pstate);
            dtablespace = defel;
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("option \"%s\" not recognized", defel->defname),
                     parser_errposition(pstate, defel->location)));
    }
 
    if (dtablespace)
    {
        /*
         * While the SET TABLESPACE syntax doesn't allow any other options,
         * somebody could write "WITH TABLESPACE ...".  Forbid any other
         * options from being specified in that case.
         */
        if (list_length(stmt->options) != 1)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("option \"%s\" cannot be specified with other options",
                            dtablespace->defname),
                     parser_errposition(pstate, dtablespace->location)));
        /* this case isn't allowed within a transaction block */
        PreventInTransactionBlock(isTopLevel, "ALTER DATABASE SET TABLESPACE");
        movedb(stmt->dbname, defGetString(dtablespace));
        return InvalidOid;
    }
 
    if (distemplate && distemplate->arg)
        dbistemplate = defGetBoolean(distemplate);
    if (dallowconnections && dallowconnections->arg)
        dballowconnections = defGetBoolean(dallowconnections);
    if (dconnlimit && dconnlimit->arg)
    {
        dbconnlimit = defGetInt32(dconnlimit);
        if (dbconnlimit < DATCONNLIMIT_UNLIMITED)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid connection limit: %d", dbconnlimit)));
    }
 
    /*
     * Get the old tuple.  We don't need a lock on the database per se,
     * because we're not going to do anything that would mess up incoming
     * connections.
     */
    rel = table_open(DatabaseRelationId, RowExclusiveLock);
    ScanKeyInit(&scankey,
                Anum_pg_database_datname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->dbname));
    scan = systable_beginscan(rel, DatabaseNameIndexId, true,
                              NULL, 1, &scankey);
    tuple = systable_getnext(scan);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" does not exist", stmt->dbname)));
 
    datform = (Form_pg_database) GETSTRUCT(tuple);
    dboid = datform->oid;
 
    if (database_is_invalid_form(datform))
    {
        ereport(FATAL,
                errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                errmsg("cannot alter invalid database \"%s\"", stmt->dbname),
                errhint("Use DROP DATABASE to drop invalid databases."));
    }
 
    if (!object_ownercheck(DatabaseRelationId, dboid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                       stmt->dbname);
 
    /*
     * In order to avoid getting locked out and having to go through
     * standalone mode, we refuse to disallow connections to the database
     * we're currently connected to.  Lockout can still happen with concurrent
     * sessions but the likeliness of that is not high enough to worry about.
     */
    if (!dballowconnections && dboid == MyDatabaseId)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("cannot disallow connections for current database")));
 
    /*
     * Build an updated tuple, perusing the information just obtained
     */
    if (distemplate)
    {
        new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);
        new_record_repl[Anum_pg_database_datistemplate - 1] = true;
    }
    if (dallowconnections)
    {
        new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);
        new_record_repl[Anum_pg_database_datallowconn - 1] = true;
    }
    if (dconnlimit)
    {
        new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);
        new_record_repl[Anum_pg_database_datconnlimit - 1] = true;
    }
 
    newtuple = heap_modify_tuple(tuple, RelationGetDescr(rel), new_record,
                                 new_record_nulls, new_record_repl);
    CatalogTupleUpdate(rel, &tuple->t_self, newtuple);
 
    InvokeObjectPostAlterHook(DatabaseRelationId, dboid, 0);
 
    systable_endscan(scan);
 
    /* Close pg_database, but keep lock till commit */
    table_close(rel, NoLock);
 
    return dboid;
}
 
 
/*
 * ALTER DATABASE name REFRESH COLLATION VERSION
 */
ObjectAddress
AlterDatabaseRefreshColl(AlterDatabaseRefreshCollStmt *stmt)
{
    Relation    rel;
    ScanKeyData scankey;
    SysScanDesc scan;
    Oid         db_id;
    HeapTuple   tuple;
    Form_pg_database datForm;
    ObjectAddress address;
    Datum       datum;
    bool        isnull;
    char       *oldversion;
    char       *newversion;
 
    rel = table_open(DatabaseRelationId, RowExclusiveLock);
    ScanKeyInit(&scankey,
                Anum_pg_database_datname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->dbname));
    scan = systable_beginscan(rel, DatabaseNameIndexId, true,
                              NULL, 1, &scankey);
    tuple = systable_getnext(scan);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" does not exist", stmt->dbname)));
 
    datForm = (Form_pg_database) GETSTRUCT(tuple);
    db_id = datForm->oid;
 
    if (!object_ownercheck(DatabaseRelationId, db_id, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                       stmt->dbname);
 
    datum = heap_getattr(tuple, Anum_pg_database_datcollversion, RelationGetDescr(rel), &isnull);
    oldversion = isnull ? NULL : TextDatumGetCString(datum);
 
    datum = heap_getattr(tuple, datForm->datlocprovider == COLLPROVIDER_ICU ? Anum_pg_database_daticulocale : Anum_pg_database_datcollate, RelationGetDescr(rel), &isnull);
    if (isnull)
        elog(ERROR, "unexpected null in pg_database");
    newversion = get_collation_actual_version(datForm->datlocprovider, TextDatumGetCString(datum));
 
    /* cannot change from NULL to non-NULL or vice versa */
    if ((!oldversion && newversion) || (oldversion && !newversion))
        elog(ERROR, "invalid collation version change");
    else if (oldversion && newversion && strcmp(newversion, oldversion) != 0)
    {
        bool        nulls[Natts_pg_database] = {0};
        bool        replaces[Natts_pg_database] = {0};
        Datum       values[Natts_pg_database] = {0};
 
        ereport(NOTICE,
                (errmsg("changing version from %s to %s",
                        oldversion, newversion)));
 
        values[Anum_pg_database_datcollversion - 1] = CStringGetTextDatum(newversion);
        replaces[Anum_pg_database_datcollversion - 1] = true;
 
        tuple = heap_modify_tuple(tuple, RelationGetDescr(rel),
                                  values, nulls, replaces);
        CatalogTupleUpdate(rel, &tuple->t_self, tuple);
        heap_freetuple(tuple);
    }
    else
        ereport(NOTICE,
                (errmsg("version has not changed")));
 
    InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
 
    ObjectAddressSet(address, DatabaseRelationId, db_id);
 
    systable_endscan(scan);
 
    table_close(rel, NoLock);
 
    return address;
}
 
 
/*
 * ALTER DATABASE name SET ...
 */
Oid
AlterDatabaseSet(AlterDatabaseSetStmt *stmt)
{
    Oid         datid = get_database_oid(stmt->dbname, false);
 
    /*
     * Obtain a lock on the database and make sure it didn't go away in the
     * meantime.
     */
    shdepLockAndCheckObject(DatabaseRelationId, datid);
 
    if (!object_ownercheck(DatabaseRelationId, datid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                       stmt->dbname);
 
    AlterSetting(datid, InvalidOid, stmt->setstmt);
 
    UnlockSharedObject(DatabaseRelationId, datid, 0, AccessShareLock);
 
    return datid;
}
 
 
/*
 * ALTER DATABASE name OWNER TO newowner
 */
ObjectAddress
AlterDatabaseOwner(const char *dbname, Oid newOwnerId)
{
    Oid         db_id;
    HeapTuple   tuple;
    Relation    rel;
    ScanKeyData scankey;
    SysScanDesc scan;
    Form_pg_database datForm;
    ObjectAddress address;
 
    /*
     * Get the old tuple.  We don't need a lock on the database per se,
     * because we're not going to do anything that would mess up incoming
     * connections.
     */
    rel = table_open(DatabaseRelationId, RowExclusiveLock);
    ScanKeyInit(&scankey,
                Anum_pg_database_datname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(dbname));
    scan = systable_beginscan(rel, DatabaseNameIndexId, true,
                              NULL, 1, &scankey);
    tuple = systable_getnext(scan);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" does not exist", dbname)));
 
    datForm = (Form_pg_database) GETSTRUCT(tuple);
    db_id = datForm->oid;
 
    /*
     * If the new owner is the same as the existing owner, consider the
     * command to have succeeded.  This is to be consistent with other
     * objects.
     */
    if (datForm->datdba != newOwnerId)
    {
        Datum       repl_val[Natts_pg_database];
        bool        repl_null[Natts_pg_database] = {0};
        bool        repl_repl[Natts_pg_database] = {0};
        Acl        *newAcl;
        Datum       aclDatum;
        bool        isNull;
        HeapTuple   newtuple;
 
        /* Otherwise, must be owner of the existing object */
        if (!object_ownercheck(DatabaseRelationId, db_id, GetUserId()))
            aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
                           dbname);
 
        /* Must be able to become new owner */
        check_can_set_role(GetUserId(), newOwnerId);
 
        /*
         * must have createdb rights
         *
         * NOTE: This is different from other alter-owner checks in that the
         * current user is checked for createdb privileges instead of the
         * destination owner.  This is consistent with the CREATE case for
         * databases.  Because superusers will always have this right, we need
         * no special case for them.
         */
        if (!have_createdb_privilege())
            ereport(ERROR,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission denied to change owner of database")));
 
        repl_repl[Anum_pg_database_datdba - 1] = true;
        repl_val[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(newOwnerId);
 
        /*
         * Determine the modified ACL for the new owner.  This is only
         * necessary when the ACL is non-null.
         */
        aclDatum = heap_getattr(tuple,
                                Anum_pg_database_datacl,
                                RelationGetDescr(rel),
                                &isNull);
        if (!isNull)
        {
            newAcl = aclnewowner(DatumGetAclP(aclDatum),
                                 datForm->datdba, newOwnerId);
            repl_repl[Anum_pg_database_datacl - 1] = true;
            repl_val[Anum_pg_database_datacl - 1] = PointerGetDatum(newAcl);
        }
 
        newtuple = heap_modify_tuple(tuple, RelationGetDescr(rel), repl_val, repl_null, repl_repl);
        CatalogTupleUpdate(rel, &newtuple->t_self, newtuple);
 
        heap_freetuple(newtuple);
 
        /* Update owner dependency reference */
        changeDependencyOnOwner(DatabaseRelationId, db_id, newOwnerId);
    }
 
    InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
 
    ObjectAddressSet(address, DatabaseRelationId, db_id);
 
    systable_endscan(scan);
 
    /* Close pg_database, but keep lock till commit */
    table_close(rel, NoLock);
 
    return address;
}
 
 
Datum
pg_database_collation_actual_version(PG_FUNCTION_ARGS)
{
    Oid         dbid = PG_GETARG_OID(0);
    HeapTuple   tp;
    char        datlocprovider;
    Datum       datum;
    char       *version;
 
    tp = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(dbid));
    if (!HeapTupleIsValid(tp))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("database with OID %u does not exist", dbid)));
 
    datlocprovider = ((Form_pg_database) GETSTRUCT(tp))->datlocprovider;
 
    datum = SysCacheGetAttrNotNull(DATABASEOID, tp, datlocprovider == COLLPROVIDER_ICU ? Anum_pg_database_daticulocale : Anum_pg_database_datcollate);
    version = get_collation_actual_version(datlocprovider, TextDatumGetCString(datum));
 
    ReleaseSysCache(tp);
 
    if (version)
        PG_RETURN_TEXT_P(cstring_to_text(version));
    else
        PG_RETURN_NULL();
}
 
 
/*
 * Helper functions
 */
 
/*
 * Look up info about the database named "name".  If the database exists,
 * obtain the specified lock type on it, fill in any of the remaining
 * parameters that aren't NULL, and return true.  If no such database,
 * return false.
 */
static bool
get_db_info(const char *name, LOCKMODE lockmode,
            Oid *dbIdP, Oid *ownerIdP,
            int *encodingP, bool *dbIsTemplateP, bool *dbAllowConnP,
            TransactionId *dbFrozenXidP, MultiXactId *dbMinMultiP,
            Oid *dbTablespace, char **dbCollate, char **dbCtype, char **dbIculocale,
            char **dbIcurules,
            char *dbLocProvider,
            char **dbCollversion)
{
    bool        result = false;
    Relation    relation;
 
    Assert(name);
 
    /* Caller may wish to grab a better lock on pg_database beforehand... */
    relation = table_open(DatabaseRelationId, AccessShareLock);
 
    /*
     * Loop covers the rare case where the database is renamed before we can
     * lock it.  We try again just in case we can find a new one of the same
     * name.
     */
    for (;;)
    {
        ScanKeyData scanKey;
        SysScanDesc scan;
        HeapTuple   tuple;
        Oid         dbOid;
 
        /*
         * there's no syscache for database-indexed-by-name, so must do it the
         * hard way
         */
        ScanKeyInit(&scanKey,
                    Anum_pg_database_datname,
                    BTEqualStrategyNumber, F_NAMEEQ,
                    CStringGetDatum(name));
 
        scan = systable_beginscan(relation, DatabaseNameIndexId, true,
                                  NULL, 1, &scanKey);
 
        tuple = systable_getnext(scan);
 
        if (!HeapTupleIsValid(tuple))
        {
            /* definitely no database of that name */
            systable_endscan(scan);
            break;
        }
 
        dbOid = ((Form_pg_database) GETSTRUCT(tuple))->oid;
 
        systable_endscan(scan);
 
        /*
         * Now that we have a database OID, we can try to lock the DB.
         */
        if (lockmode != NoLock)
            LockSharedObject(DatabaseRelationId, dbOid, 0, lockmode);
 
        /*
         * And now, re-fetch the tuple by OID.  If it's still there and still
         * the same name, we win; else, drop the lock and loop back to try
         * again.
         */
        tuple = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(dbOid));
        if (HeapTupleIsValid(tuple))
        {
            Form_pg_database dbform = (Form_pg_database) GETSTRUCT(tuple);
 
            if (strcmp(name, NameStr(dbform->datname)) == 0)
            {
                Datum       datum;
                bool        isnull;
 
                /* oid of the database */
                if (dbIdP)
                    *dbIdP = dbOid;
                /* oid of the owner */
                if (ownerIdP)
                    *ownerIdP = dbform->datdba;
                /* character encoding */
                if (encodingP)
                    *encodingP = dbform->encoding;
                /* allowed as template? */
                if (dbIsTemplateP)
                    *dbIsTemplateP = dbform->datistemplate;
                /* allowing connections? */
                if (dbAllowConnP)
                    *dbAllowConnP = dbform->datallowconn;
                /* limit of frozen XIDs */
                if (dbFrozenXidP)
                    *dbFrozenXidP = dbform->datfrozenxid;
                /* minimum MultiXactId */
                if (dbMinMultiP)
                    *dbMinMultiP = dbform->datminmxid;
                /* default tablespace for this database */
                if (dbTablespace)
                    *dbTablespace = dbform->dattablespace;
                /* default locale settings for this database */
                if (dbLocProvider)
                    *dbLocProvider = dbform->datlocprovider;
                if (dbCollate)
                {
                    datum = SysCacheGetAttrNotNull(DATABASEOID, tuple, Anum_pg_database_datcollate);
                    *dbCollate = TextDatumGetCString(datum);
                }
                if (dbCtype)
                {
                    datum = SysCacheGetAttrNotNull(DATABASEOID, tuple, Anum_pg_database_datctype);
                    *dbCtype = TextDatumGetCString(datum);
                }
                if (dbIculocale)
                {
                    datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticulocale, &isnull);
                    if (isnull)
                        *dbIculocale = NULL;
                    else
                        *dbIculocale = TextDatumGetCString(datum);
                }
                if (dbIcurules)
                {
                    datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_daticurules, &isnull);
                    if (isnull)
                        *dbIcurules = NULL;
                    else
                        *dbIcurules = TextDatumGetCString(datum);
                }
                if (dbCollversion)
                {
                    datum = SysCacheGetAttr(DATABASEOID, tuple, Anum_pg_database_datcollversion, &isnull);
                    if (isnull)
                        *dbCollversion = NULL;
                    else
                        *dbCollversion = TextDatumGetCString(datum);
                }
                ReleaseSysCache(tuple);
                result = true;
                break;
            }
            /* can only get here if it was just renamed */
            ReleaseSysCache(tuple);
        }
 
        if (lockmode != NoLock)
            UnlockSharedObject(DatabaseRelationId, dbOid, 0, lockmode);
    }
 
    table_close(relation, AccessShareLock);
 
    return result;
}
 
/* Check if current user has createdb privileges */
bool
have_createdb_privilege(void)
{
    bool        result = false;
    HeapTuple   utup;
 
    /* Superusers can always do everything */
    if (superuser())
        return true;
 
    utup = SearchSysCache1(AUTHOID, ObjectIdGetDatum(GetUserId()));
    if (HeapTupleIsValid(utup))
    {
        result = ((Form_pg_authid) GETSTRUCT(utup))->rolcreatedb;
        ReleaseSysCache(utup);
    }
    return result;
}
 
/*
 * Remove tablespace directories
 *
 * We don't know what tablespaces db_id is using, so iterate through all
 * tablespaces removing <tablespace>/db_id
 */
static void
remove_dbtablespaces(Oid db_id)
{
    Relation    rel;
    TableScanDesc scan;
    HeapTuple   tuple;
    List       *ltblspc = NIL;
    ListCell   *cell;
    int         ntblspc;
    int         i;
    Oid        *tablespace_ids;
 
    rel = table_open(TableSpaceRelationId, AccessShareLock);
    scan = table_beginscan_catalog(rel, 0, NULL);
    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        Form_pg_tablespace spcform = (Form_pg_tablespace) GETSTRUCT(tuple);
        Oid         dsttablespace = spcform->oid;
        char       *dstpath;
        struct stat st;
 
        /* Don't mess with the global tablespace */
        if (dsttablespace == GLOBALTABLESPACE_OID)
            continue;
 
        dstpath = GetDatabasePath(db_id, dsttablespace);
 
        if (lstat(dstpath, &st) < 0 || !S_ISDIR(st.st_mode))
        {
            /* Assume we can ignore it */
            pfree(dstpath);
            continue;
        }
 
        if (!rmtree(dstpath, true))
            ereport(WARNING,
                    (errmsg("some useless files may be left behind in old database directory \"%s\"",
                            dstpath)));
 
        ltblspc = lappend_oid(ltblspc, dsttablespace);
        pfree(dstpath);
    }
 
    ntblspc = list_length(ltblspc);
    if (ntblspc == 0)
    {
        table_endscan(scan);
        table_close(rel, AccessShareLock);
        return;
    }
 
    tablespace_ids = (Oid *) palloc(ntblspc * sizeof(Oid));
    i = 0;
    foreach(cell, ltblspc)
        tablespace_ids[i++] = lfirst_oid(cell);
 
    /* Record the filesystem change in XLOG */
    {
        xl_dbase_drop_rec xlrec;
 
        xlrec.db_id = db_id;
        xlrec.ntablespaces = ntblspc;
 
        XLogBeginInsert();
        XLogRegisterData((char *) &xlrec, MinSizeOfDbaseDropRec);
        XLogRegisterData((char *) tablespace_ids, ntblspc * sizeof(Oid));
 
        (void) XLogInsert(RM_DBASE_ID,
                          XLOG_DBASE_DROP | XLR_SPECIAL_REL_UPDATE);
    }
 
    list_free(ltblspc);
    pfree(tablespace_ids);
 
    table_endscan(scan);
    table_close(rel, AccessShareLock);
}
 
/*
 * Check for existing files that conflict with a proposed new DB OID;
 * return true if there are any
 *
 * If there were a subdirectory in any tablespace matching the proposed new
 * OID, we'd get a create failure due to the duplicate name ... and then we'd
 * try to remove that already-existing subdirectory during the cleanup in
 * remove_dbtablespaces.  Nuking existing files seems like a bad idea, so
 * instead we make this extra check before settling on the OID of the new
 * database.  This exactly parallels what GetNewRelFileNumber() does for table
 * relfilenumber values.
 */
static bool
check_db_file_conflict(Oid db_id)
{
    bool        result = false;
    Relation    rel;
    TableScanDesc scan;
    HeapTuple   tuple;
 
    rel = table_open(TableSpaceRelationId, AccessShareLock);
    scan = table_beginscan_catalog(rel, 0, NULL);
    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        Form_pg_tablespace spcform = (Form_pg_tablespace) GETSTRUCT(tuple);
        Oid         dsttablespace = spcform->oid;
        char       *dstpath;
        struct stat st;
 
        /* Don't mess with the global tablespace */
        if (dsttablespace == GLOBALTABLESPACE_OID)
            continue;
 
        dstpath = GetDatabasePath(db_id, dsttablespace);
 
        if (lstat(dstpath, &st) == 0)
        {
            /* Found a conflicting file (or directory, whatever) */
            pfree(dstpath);
            result = true;
            break;
        }
 
        pfree(dstpath);
    }
 
    table_endscan(scan);
    table_close(rel, AccessShareLock);
 
    return result;
}
 
/*
 * Issue a suitable errdetail message for a busy database
 */
static int
errdetail_busy_db(int notherbackends, int npreparedxacts)
{
    if (notherbackends > 0 && npreparedxacts > 0)
 
        /*
         * We don't deal with singular versus plural here, since gettext
         * doesn't support multiple plurals in one string.
         */
        errdetail("There are %d other session(s) and %d prepared transaction(s) using the database.",
                  notherbackends, npreparedxacts);
    else if (notherbackends > 0)
        errdetail_plural("There is %d other session using the database.",
                         "There are %d other sessions using the database.",
                         notherbackends,
                         notherbackends);
    else
        errdetail_plural("There is %d prepared transaction using the database.",
                         "There are %d prepared transactions using the database.",
                         npreparedxacts,
                         npreparedxacts);
    return 0;                   /* just to keep ereport macro happy */
}
 
/*
 * get_database_oid - given a database name, look up the OID
 *
 * If missing_ok is false, throw an error if database name not found.  If
 * true, just return InvalidOid.
 */
Oid
get_database_oid(const char *dbname, bool missing_ok)
{
    Relation    pg_database;
    ScanKeyData entry[1];
    SysScanDesc scan;
    HeapTuple   dbtuple;
    Oid         oid;
 
    /*
     * There's no syscache for pg_database indexed by name, so we must look
     * the hard way.
     */
    pg_database = table_open(DatabaseRelationId, AccessShareLock);
    ScanKeyInit(&entry[0],
                Anum_pg_database_datname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(dbname));
    scan = systable_beginscan(pg_database, DatabaseNameIndexId, true,
                              NULL, 1, entry);
 
    dbtuple = systable_getnext(scan);
 
    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(dbtuple))
        oid = ((Form_pg_database) GETSTRUCT(dbtuple))->oid;
    else
        oid = InvalidOid;
 
    systable_endscan(scan);
    table_close(pg_database, AccessShareLock);
 
    if (!OidIsValid(oid) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" does not exist",
                        dbname)));
 
    return oid;
}
 
 
/*
 * get_database_name - given a database OID, look up the name
 *
 * Returns a palloc'd string, or NULL if no such database.
 */
char *
get_database_name(Oid dbid)
{
    HeapTuple   dbtuple;
    char       *result;
 
    dbtuple = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(dbid));
    if (HeapTupleIsValid(dbtuple))
    {
        result = pstrdup(NameStr(((Form_pg_database) GETSTRUCT(dbtuple))->datname));
        ReleaseSysCache(dbtuple);
    }
    else
        result = NULL;
 
    return result;
}
 
 
/*
 * While dropping a database the pg_database row is marked invalid, but the
 * catalog contents still exist. Connections to such a database are not
 * allowed.
 */
bool
database_is_invalid_form(Form_pg_database datform)
{
    return datform->datconnlimit == DATCONNLIMIT_INVALID_DB;
}
 
 
/*
 * Convenience wrapper around database_is_invalid_form()
 */
bool
database_is_invalid_oid(Oid dboid)
{
    HeapTuple   dbtup;
    Form_pg_database dbform;
    bool        invalid;
 
    dbtup = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(dboid));
    if (!HeapTupleIsValid(dbtup))
        elog(ERROR, "cache lookup failed for database %u", dboid);
    dbform = (Form_pg_database) GETSTRUCT(dbtup);
 
    invalid = database_is_invalid_form(dbform);
 
    ReleaseSysCache(dbtup);
 
    return invalid;
}
 
 
/*
 * recovery_create_dbdir()
 *
 * During recovery, there's a case where we validly need to recover a missing
 * tablespace directory so that recovery can continue.  This happens when
 * recovery wants to create a database but the holding tablespace has been
 * removed before the server stopped.  Since we expect that the directory will
 * be gone before reaching recovery consistency, and we have no knowledge about
 * the tablespace other than its OID here, we create a real directory under
 * pg_tblspc here instead of restoring the symlink.
 *
 * If only_tblspc is true, then the requested directory must be in pg_tblspc/
 */
static void
recovery_create_dbdir(char *path, bool only_tblspc)
{
    struct stat st;
 
    Assert(RecoveryInProgress());
 
    if (stat(path, &st) == 0)
        return;
 
    if (only_tblspc && strstr(path, "pg_tblspc/") == NULL)
        elog(PANIC, "requested to created invalid directory: %s", path);
 
    if (reachedConsistency && !allow_in_place_tablespaces)
        ereport(PANIC,
                errmsg("missing directory \"%s\"", path));
 
    elog(reachedConsistency ? WARNING : DEBUG1,
         "creating missing directory: %s", path);
 
    if (pg_mkdir_p(path, pg_dir_create_mode) != 0)
        ereport(PANIC,
                errmsg("could not create missing directory \"%s\": %m", path));
}
 
 
/*
 * DATABASE resource manager's routines
 */
void
dbase_redo(XLogReaderState *record)
{
    uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
 
    /* Backup blocks are not used in dbase records */
    Assert(!XLogRecHasAnyBlockRefs(record));
 
    if (info == XLOG_DBASE_CREATE_FILE_COPY)
    {
        xl_dbase_create_file_copy_rec *xlrec =
            (xl_dbase_create_file_copy_rec *) XLogRecGetData(record);
        char       *src_path;
        char       *dst_path;
        char       *parent_path;
        struct stat st;
 
        src_path = GetDatabasePath(xlrec->src_db_id, xlrec->src_tablespace_id);
        dst_path = GetDatabasePath(xlrec->db_id, xlrec->tablespace_id);
 
        /*
         * Our theory for replaying a CREATE is to forcibly drop the target
         * subdirectory if present, then re-copy the source data. This may be
         * more work than needed, but it is simple to implement.
         */
        if (stat(dst_path, &st) == 0 && S_ISDIR(st.st_mode))
        {
            if (!rmtree(dst_path, true))
                /* If this failed, copydir() below is going to error. */
                ereport(WARNING,
                        (errmsg("some useless files may be left behind in old database directory \"%s\"",
                                dst_path)));
        }
 
        /*
         * If the parent of the target path doesn't exist, create it now. This
         * enables us to create the target underneath later.
         */
        parent_path = pstrdup(dst_path);
        get_parent_directory(parent_path);
        if (stat(parent_path, &st) < 0)
        {
            if (errno != ENOENT)
                ereport(FATAL,
                        errmsg("could not stat directory \"%s\": %m",
                               dst_path));
 
            /* create the parent directory if needed and valid */
            recovery_create_dbdir(parent_path, true);
        }
        pfree(parent_path);
 
        /*
         * There's a case where the copy source directory is missing for the
         * same reason above.  Create the empty source directory so that
         * copydir below doesn't fail.  The directory will be dropped soon by
         * recovery.
         */
        if (stat(src_path, &st) < 0 && errno == ENOENT)
            recovery_create_dbdir(src_path, false);
 
        /*
         * Force dirty buffers out to disk, to ensure source database is
         * up-to-date for the copy.
         */
        FlushDatabaseBuffers(xlrec->src_db_id);
 
        /* Close all sgmr fds in all backends. */
        WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
 
        /*
         * Copy this subdirectory to the new location
         *
         * We don't need to copy subdirectories
         */
        copydir(src_path, dst_path, false);
 
        pfree(src_path);
        pfree(dst_path);
    }
    else if (info == XLOG_DBASE_CREATE_WAL_LOG)
    {
        xl_dbase_create_wal_log_rec *xlrec =
            (xl_dbase_create_wal_log_rec *) XLogRecGetData(record);
        char       *dbpath;
        char       *parent_path;
 
        dbpath = GetDatabasePath(xlrec->db_id, xlrec->tablespace_id);
 
        /* create the parent directory if needed and valid */
        parent_path = pstrdup(dbpath);
        get_parent_directory(parent_path);
        recovery_create_dbdir(parent_path, true);
 
        /* Create the database directory with the version file. */
        CreateDirAndVersionFile(dbpath, xlrec->db_id, xlrec->tablespace_id,
                                true);
        pfree(dbpath);
    }
    else if (info == XLOG_DBASE_DROP)
    {
        xl_dbase_drop_rec *xlrec = (xl_dbase_drop_rec *) XLogRecGetData(record);
        char       *dst_path;
        int         i;
 
        if (InHotStandby)
        {
            /*
             * Lock database while we resolve conflicts to ensure that
             * InitPostgres() cannot fully re-execute concurrently. This
             * avoids backends re-connecting automatically to same database,
             * which can happen in some cases.
             *
             * This will lock out walsenders trying to connect to db-specific
             * slots for logical decoding too, so it's safe for us to drop
             * slots.
             */
            LockSharedObjectForSession(DatabaseRelationId, xlrec->db_id, 0, AccessExclusiveLock);
            ResolveRecoveryConflictWithDatabase(xlrec->db_id);
        }
 
        /* Drop any database-specific replication slots */
        ReplicationSlotsDropDBSlots(xlrec->db_id);
 
        /* Drop pages for this database that are in the shared buffer cache */
        DropDatabaseBuffers(xlrec->db_id);
 
        /* Also, clean out any fsync requests that might be pending in md.c */
        ForgetDatabaseSyncRequests(xlrec->db_id);
 
        /* Clean out the xlog relcache too */
        XLogDropDatabase(xlrec->db_id);
 
        /* Close all sgmr fds in all backends. */
        WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
 
        for (i = 0; i < xlrec->ntablespaces; i++)
        {
            dst_path = GetDatabasePath(xlrec->db_id, xlrec->tablespace_ids[i]);
 
            /* And remove the physical files */
            if (!rmtree(dst_path, true))
                ereport(WARNING,
                        (errmsg("some useless files may be left behind in old database directory \"%s\"",
                                dst_path)));
            pfree(dst_path);
        }
 
        if (InHotStandby)
        {
            /*
             * Release locks prior to commit. XXX There is a race condition
             * here that may allow backends to reconnect, but the window for
             * this is small because the gap between here and commit is mostly
             * fairly small and it is unlikely that people will be dropping
             * databases that we are trying to connect to anyway.
             */
            UnlockSharedObjectForSession(DatabaseRelationId, xlrec->db_id, 0, AccessExclusiveLock);
        }
    }
    else
        elog(PANIC, "dbase_redo: unknown op code %u", info);
}