tablespace.c

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/*-------------------------------------------------------------------------
 *
 * tablespace.c
 *    Commands to manipulate table spaces
 *
 * Tablespaces in PostgreSQL are designed to allow users to determine
 * where the data file(s) for a given database object reside on the file
 * system.
 *
 * A tablespace represents a directory on the file system. At tablespace
 * creation time, the directory must be empty. To simplify things and
 * remove the possibility of having file name conflicts, we isolate
 * files within a tablespace into database-specific subdirectories.
 *
 * To support file access via the information given in RelFileLocator, we
 * maintain a symbolic-link map in $PGDATA/pg_tblspc. The symlinks are
 * named by tablespace OIDs and point to the actual tablespace directories.
 * There is also a per-cluster version directory in each tablespace.
 * Thus the full path to an arbitrary file is
 *          $PGDATA/pg_tblspc/spcoid/PG_MAJORVER_CATVER/dboid/relfilenumber
 * e.g.
 *          $PGDATA/pg_tblspc/20981/PG_9.0_201002161/719849/83292814
 *
 * There are two tablespaces created at initdb time: pg_global (for shared
 * tables) and pg_default (for everything else).  For backwards compatibility
 * and to remain functional on platforms without symlinks, these tablespaces
 * are accessed specially: they are respectively
 *          $PGDATA/global/relfilenumber
 *          $PGDATA/base/dboid/relfilenumber
 *
 * To allow CREATE DATABASE to give a new database a default tablespace
 * that's different from the template database's default, we make the
 * provision that a zero in pg_class.reltablespace means the database's
 * default tablespace.  Without this, CREATE DATABASE would have to go in
 * and munge the system catalogs of the new database.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/tablespace.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>
 
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/reloptions.h"
#include "access/sysattr.h"
#include "access/tableam.h"
#include "access/xact.h"
#include "access/xloginsert.h"
#include "access/xlogutils.h"
#include "catalog/binary_upgrade.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_tablespace.h"
#include "commands/comment.h"
#include "commands/seclabel.h"
#include "commands/tablecmds.h"
#include "commands/tablespace.h"
#include "common/file_perm.h"
#include "miscadmin.h"
#include "postmaster/bgwriter.h"
#include "storage/fd.h"
#include "storage/lmgr.h"
#include "storage/standby.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/guc_hooks.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/varlena.h"
 
/* GUC variables */
char       *default_tablespace = NULL;
char       *temp_tablespaces = NULL;
bool        allow_in_place_tablespaces = false;
 
Oid         binary_upgrade_next_pg_tablespace_oid = InvalidOid;
 
static void create_tablespace_directories(const char *location,
                                          const Oid tablespaceoid);
static bool destroy_tablespace_directories(Oid tablespaceoid, bool redo);
 
 
/*
 * Each database using a table space is isolated into its own name space
 * by a subdirectory named for the database OID.  On first creation of an
 * object in the tablespace, create the subdirectory.  If the subdirectory
 * already exists, fall through quietly.
 *
 * isRedo indicates that we are creating an object during WAL replay.
 * In this case we will cope with the possibility of the tablespace
 * directory not being there either --- this could happen if we are
 * replaying an operation on a table in a subsequently-dropped tablespace.
 * We handle this by making a directory in the place where the tablespace
 * symlink would normally be.  This isn't an exact replay of course, but
 * it's the best we can do given the available information.
 *
 * If tablespaces are not supported, we still need it in case we have to
 * re-create a database subdirectory (of $PGDATA/base) during WAL replay.
 */
void
TablespaceCreateDbspace(Oid spcOid, Oid dbOid, bool isRedo)
{
    struct stat st;
    char       *dir;
 
    /*
     * The global tablespace doesn't have per-database subdirectories, so
     * nothing to do for it.
     */
    if (spcOid == GLOBALTABLESPACE_OID)
        return;
 
    Assert(OidIsValid(spcOid));
    Assert(OidIsValid(dbOid));
 
    dir = GetDatabasePath(dbOid, spcOid);
 
    if (stat(dir, &st) < 0)
    {
        /* Directory does not exist? */
        if (errno == ENOENT)
        {
            /*
             * Acquire TablespaceCreateLock to ensure that no DROP TABLESPACE
             * or TablespaceCreateDbspace is running concurrently.
             */
            LWLockAcquire(TablespaceCreateLock, LW_EXCLUSIVE);
 
            /*
             * Recheck to see if someone created the directory while we were
             * waiting for lock.
             */
            if (stat(dir, &st) == 0 && S_ISDIR(st.st_mode))
            {
                /* Directory was created */
            }
            else
            {
                /* Directory creation failed? */
                if (MakePGDirectory(dir) < 0)
                {
                    /* Failure other than not exists or not in WAL replay? */
                    if (errno != ENOENT || !isRedo)
                        ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not create directory \"%s\": %m",
                                        dir)));
 
                    /*
                     * During WAL replay, it's conceivable that several levels
                     * of directories are missing if tablespaces are dropped
                     * further ahead of the WAL stream than we're currently
                     * replaying.  An easy way forward is to create them as
                     * plain directories and hope they are removed by further
                     * WAL replay if necessary.  If this also fails, there is
                     * trouble we cannot get out of, so just report that and
                     * bail out.
                     */
                    if (pg_mkdir_p(dir, pg_dir_create_mode) < 0)
                        ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not create directory \"%s\": %m",
                                        dir)));
                }
            }
 
            LWLockRelease(TablespaceCreateLock);
        }
        else
        {
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not stat directory \"%s\": %m", dir)));
        }
    }
    else
    {
        /* Is it not a directory? */
        if (!S_ISDIR(st.st_mode))
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("\"%s\" exists but is not a directory",
                            dir)));
    }
 
    pfree(dir);
}
 
/*
 * Create a table space
 *
 * Only superusers can create a tablespace. This seems a reasonable restriction
 * since we're determining the system layout and, anyway, we probably have
 * root if we're doing this kind of activity
 */
Oid
CreateTableSpace(CreateTableSpaceStmt *stmt)
{
    Relation    rel;
    Datum       values[Natts_pg_tablespace];
    bool        nulls[Natts_pg_tablespace] = {0};
    HeapTuple   tuple;
    Oid         tablespaceoid;
    char       *location;
    Oid         ownerId;
    Datum       newOptions;
    bool        in_place;
 
    /* Must be superuser */
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied to create tablespace \"%s\"",
                        stmt->tablespacename),
                 errhint("Must be superuser to create a tablespace.")));
 
    /* However, the eventual owner of the tablespace need not be */
    if (stmt->owner)
        ownerId = get_rolespec_oid(stmt->owner, false);
    else
        ownerId = GetUserId();
 
    /* Unix-ify the offered path, and strip any trailing slashes */
    location = pstrdup(stmt->location);
    canonicalize_path(location);
 
    /* disallow quotes, else CREATE DATABASE would be at risk */
    if (strchr(location, '\''))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_NAME),
                 errmsg("tablespace location cannot contain single quotes")));
 
    in_place = allow_in_place_tablespaces && strlen(location) == 0;
 
    /*
     * Allowing relative paths seems risky
     *
     * This also helps us ensure that location is not empty or whitespace,
     * unless specifying a developer-only in-place tablespace.
     */
    if (!in_place && !is_absolute_path(location))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("tablespace location must be an absolute path")));
 
    /*
     * Check that location isn't too long. Remember that we're going to append
     * 'PG_XXX/<dboid>/<relid>_<fork>.<nnn>'.  FYI, we never actually
     * reference the whole path here, but MakePGDirectory() uses the first two
     * parts.
     */
    if (strlen(location) + 1 + strlen(TABLESPACE_VERSION_DIRECTORY) + 1 +
        OIDCHARS + 1 + OIDCHARS + 1 + FORKNAMECHARS + 1 + OIDCHARS > MAXPGPATH)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("tablespace location \"%s\" is too long",
                        location)));
 
    /* Warn if the tablespace is in the data directory. */
    if (path_is_prefix_of_path(DataDir, location))
        ereport(WARNING,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("tablespace location should not be inside the data directory")));
 
    /*
     * Disallow creation of tablespaces named "pg_xxx"; we reserve this
     * namespace for system purposes.
     */
    if (!allowSystemTableMods && IsReservedName(stmt->tablespacename))
        ereport(ERROR,
                (errcode(ERRCODE_RESERVED_NAME),
                 errmsg("unacceptable tablespace name \"%s\"",
                        stmt->tablespacename),
                 errdetail("The prefix \"pg_\" is reserved for system tablespaces.")));
 
    /*
     * If built with appropriate switch, whine when regression-testing
     * conventions for tablespace names are violated.
     */
#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
    if (strncmp(stmt->tablespacename, "regress_", 8) != 0)
        elog(WARNING, "tablespaces created by regression test cases should have names starting with \"regress_\"");
#endif
 
    /*
     * Check that there is no other tablespace by this name.  (The unique
     * index would catch this anyway, but might as well give a friendlier
     * message.)
     */
    if (OidIsValid(get_tablespace_oid(stmt->tablespacename, true)))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("tablespace \"%s\" already exists",
                        stmt->tablespacename)));
 
    /*
     * Insert tuple into pg_tablespace.  The purpose of doing this first is to
     * lock the proposed tablename against other would-be creators. The
     * insertion will roll back if we find problems below.
     */
    rel = table_open(TableSpaceRelationId, RowExclusiveLock);
 
    if (IsBinaryUpgrade)
    {
        /* Use binary-upgrade override for tablespace oid */
        if (!OidIsValid(binary_upgrade_next_pg_tablespace_oid))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("pg_tablespace OID value not set when in binary upgrade mode")));
 
        tablespaceoid = binary_upgrade_next_pg_tablespace_oid;
        binary_upgrade_next_pg_tablespace_oid = InvalidOid;
    }
    else
        tablespaceoid = GetNewOidWithIndex(rel, TablespaceOidIndexId,
                                           Anum_pg_tablespace_oid);
    values[Anum_pg_tablespace_oid - 1] = ObjectIdGetDatum(tablespaceoid);
    values[Anum_pg_tablespace_spcname - 1] =
        DirectFunctionCall1(namein, CStringGetDatum(stmt->tablespacename));
    values[Anum_pg_tablespace_spcowner - 1] =
        ObjectIdGetDatum(ownerId);
    nulls[Anum_pg_tablespace_spcacl - 1] = true;
 
    /* Generate new proposed spcoptions (text array) */
    newOptions = transformRelOptions((Datum) 0,
                                     stmt->options,
                                     NULL, NULL, false, false);
    (void) tablespace_reloptions(newOptions, true);
    if (newOptions != (Datum) 0)
        values[Anum_pg_tablespace_spcoptions - 1] = newOptions;
    else
        nulls[Anum_pg_tablespace_spcoptions - 1] = true;
 
    tuple = heap_form_tuple(rel->rd_att, values, nulls);
 
    CatalogTupleInsert(rel, tuple);
 
    heap_freetuple(tuple);
 
    /* Record dependency on owner */
    recordDependencyOnOwner(TableSpaceRelationId, tablespaceoid, ownerId);
 
    /* Post creation hook for new tablespace */
    InvokeObjectPostCreateHook(TableSpaceRelationId, tablespaceoid, 0);
 
    create_tablespace_directories(location, tablespaceoid);
 
    /* Record the filesystem change in XLOG */
    {
        xl_tblspc_create_rec xlrec;
 
        xlrec.ts_id = tablespaceoid;
 
        XLogBeginInsert();
        XLogRegisterData((char *) &xlrec,
                         offsetof(xl_tblspc_create_rec, ts_path));
        XLogRegisterData((char *) location, strlen(location) + 1);
 
        (void) XLogInsert(RM_TBLSPC_ID, XLOG_TBLSPC_CREATE);
    }
 
    /*
     * Force synchronous commit, to minimize the window between creating the
     * symlink on-disk and marking the transaction committed.  It's not great
     * that there is any window at all, but definitely we don't want to make
     * it larger than necessary.
     */
    ForceSyncCommit();
 
    pfree(location);
 
    /* We keep the lock on pg_tablespace until commit */
    table_close(rel, NoLock);
 
    return tablespaceoid;
}
 
/*
 * Drop a table space
 *
 * Be careful to check that the tablespace is empty.
 */
void
DropTableSpace(DropTableSpaceStmt *stmt)
{
    char       *tablespacename = stmt->tablespacename;
    TableScanDesc scandesc;
    Relation    rel;
    HeapTuple   tuple;
    Form_pg_tablespace spcform;
    ScanKeyData entry[1];
    Oid         tablespaceoid;
    char       *detail;
    char       *detail_log;
 
    /*
     * Find the target tuple
     */
    rel = table_open(TableSpaceRelationId, RowExclusiveLock);
 
    ScanKeyInit(&entry[0],
                Anum_pg_tablespace_spcname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(tablespacename));
    scandesc = table_beginscan_catalog(rel, 1, entry);
    tuple = heap_getnext(scandesc, ForwardScanDirection);
 
    if (!HeapTupleIsValid(tuple))
    {
        if (!stmt->missing_ok)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("tablespace \"%s\" does not exist",
                            tablespacename)));
        }
        else
        {
            ereport(NOTICE,
                    (errmsg("tablespace \"%s\" does not exist, skipping",
                            tablespacename)));
            table_endscan(scandesc);
            table_close(rel, NoLock);
        }
        return;
    }
 
    spcform = (Form_pg_tablespace) GETSTRUCT(tuple);
    tablespaceoid = spcform->oid;
 
    /* Must be tablespace owner */
    if (!object_ownercheck(TableSpaceRelationId, tablespaceoid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_TABLESPACE,
                       tablespacename);
 
    /* Disallow drop of the standard tablespaces, even by superuser */
    if (IsPinnedObject(TableSpaceRelationId, tablespaceoid))
        aclcheck_error(ACLCHECK_NO_PRIV, OBJECT_TABLESPACE,
                       tablespacename);
 
    /* Check for pg_shdepend entries depending on this tablespace */
    if (checkSharedDependencies(TableSpaceRelationId, tablespaceoid,
                                &detail, &detail_log))
        ereport(ERROR,
                (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
                 errmsg("tablespace \"%s\" cannot be dropped because some objects depend on it",
                        tablespacename),
                 errdetail_internal("%s", detail),
                 errdetail_log("%s", detail_log)));
 
    /* DROP hook for the tablespace being removed */
    InvokeObjectDropHook(TableSpaceRelationId, tablespaceoid, 0);
 
    /*
     * Remove the pg_tablespace tuple (this will roll back if we fail below)
     */
    CatalogTupleDelete(rel, &tuple->t_self);
 
    table_endscan(scandesc);
 
    /*
     * Remove any comments or security labels on this tablespace.
     */
    DeleteSharedComments(tablespaceoid, TableSpaceRelationId);
    DeleteSharedSecurityLabel(tablespaceoid, TableSpaceRelationId);
 
    /*
     * Remove dependency on owner.
     */
    deleteSharedDependencyRecordsFor(TableSpaceRelationId, tablespaceoid, 0);
 
    /*
     * Acquire TablespaceCreateLock to ensure that no TablespaceCreateDbspace
     * is running concurrently.
     */
    LWLockAcquire(TablespaceCreateLock, LW_EXCLUSIVE);
 
    /*
     * Try to remove the physical infrastructure.
     */
    if (!destroy_tablespace_directories(tablespaceoid, false))
    {
        /*
         * Not all files deleted?  However, there can be lingering empty files
         * in the directories, left behind by for example DROP TABLE, that
         * have been scheduled for deletion at next checkpoint (see comments
         * in mdunlink() for details).  We could just delete them immediately,
         * but we can't tell them apart from important data files that we
         * mustn't delete.  So instead, we force a checkpoint which will clean
         * out any lingering files, and try again.
         */
        RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
 
        /*
         * On Windows, an unlinked file persists in the directory listing
         * until no process retains an open handle for the file.  The DDL
         * commands that schedule files for unlink send invalidation messages
         * directing other PostgreSQL processes to close the files, but
         * nothing guarantees they'll be processed in time.  So, we'll also
         * use a global barrier to ask all backends to close all files, and
         * wait until they're finished.
         */
        LWLockRelease(TablespaceCreateLock);
        WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
        LWLockAcquire(TablespaceCreateLock, LW_EXCLUSIVE);
 
        /* And now try again. */
        if (!destroy_tablespace_directories(tablespaceoid, false))
        {
            /* Still not empty, the files must be important then */
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("tablespace \"%s\" is not empty",
                            tablespacename)));
        }
    }
 
    /* Record the filesystem change in XLOG */
    {
        xl_tblspc_drop_rec xlrec;
 
        xlrec.ts_id = tablespaceoid;
 
        XLogBeginInsert();
        XLogRegisterData((char *) &xlrec, sizeof(xl_tblspc_drop_rec));
 
        (void) XLogInsert(RM_TBLSPC_ID, XLOG_TBLSPC_DROP);
    }
 
    /*
     * Note: because we checked that the tablespace was empty, there should be
     * no need to worry about flushing shared buffers or free space map
     * entries for relations in the tablespace.
     */
 
    /*
     * Force synchronous commit, to minimize the window between removing the
     * files on-disk and marking the transaction committed.  It's not great
     * that there is any window at all, but definitely we don't want to make
     * it larger than necessary.
     */
    ForceSyncCommit();
 
    /*
     * Allow TablespaceCreateDbspace again.
     */
    LWLockRelease(TablespaceCreateLock);
 
    /* We keep the lock on pg_tablespace until commit */
    table_close(rel, NoLock);
}
 
 
/*
 * create_tablespace_directories
 *
 *  Attempt to create filesystem infrastructure linking $PGDATA/pg_tblspc/
 *  to the specified directory
 */
static void
create_tablespace_directories(const char *location, const Oid tablespaceoid)
{
    char       *linkloc;
    char       *location_with_version_dir;
    struct stat st;
    bool        in_place;
 
    linkloc = psprintf("pg_tblspc/%u", tablespaceoid);
 
    /*
     * If we're asked to make an 'in place' tablespace, create the directory
     * directly where the symlink would normally go.  This is a developer-only
     * option for now, to facilitate regression testing.
     */
    in_place = strlen(location) == 0;
 
    if (in_place)
    {
        if (MakePGDirectory(linkloc) < 0 && errno != EEXIST)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not create directory \"%s\": %m",
                            linkloc)));
    }
 
    location_with_version_dir = psprintf("%s/%s", in_place ? linkloc : location,
                                         TABLESPACE_VERSION_DIRECTORY);
 
    /*
     * Attempt to coerce target directory to safe permissions.  If this fails,
     * it doesn't exist or has the wrong owner.  Not needed for in-place mode,
     * because in that case we created the directory with the desired
     * permissions.
     */
    if (!in_place && chmod(location, pg_dir_create_mode) != 0)
    {
        if (errno == ENOENT)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_FILE),
                     errmsg("directory \"%s\" does not exist", location),
                     InRecovery ? errhint("Create this directory for the tablespace before "
                                          "restarting the server.") : 0));
        else
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not set permissions on directory \"%s\": %m",
                            location)));
    }
 
    /*
     * The creation of the version directory prevents more than one tablespace
     * in a single location.  This imitates TablespaceCreateDbspace(), but it
     * ignores concurrency and missing parent directories.  The chmod() would
     * have failed in the absence of a parent.  pg_tablespace_spcname_index
     * prevents concurrency.
     */
    if (stat(location_with_version_dir, &st) < 0)
    {
        if (errno != ENOENT)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not stat directory \"%s\": %m",
                            location_with_version_dir)));
        else if (MakePGDirectory(location_with_version_dir) < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not create directory \"%s\": %m",
                            location_with_version_dir)));
    }
    else if (!S_ISDIR(st.st_mode))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" exists but is not a directory",
                        location_with_version_dir)));
    else if (!InRecovery)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
                 errmsg("directory \"%s\" already in use as a tablespace",
                        location_with_version_dir)));
 
    /*
     * In recovery, remove old symlink, in case it points to the wrong place.
     */
    if (!in_place && InRecovery)
        remove_tablespace_symlink(linkloc);
 
    /*
     * Create the symlink under PGDATA
     */
    if (!in_place && symlink(location, linkloc) < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not create symbolic link \"%s\": %m",
                        linkloc)));
 
    pfree(linkloc);
    pfree(location_with_version_dir);
}
 
 
/*
 * destroy_tablespace_directories
 *
 * Attempt to remove filesystem infrastructure for the tablespace.
 *
 * 'redo' indicates we are redoing a drop from XLOG; in that case we should
 * not throw an ERROR for problems, just LOG them.  The worst consequence of
 * not removing files here would be failure to release some disk space, which
 * does not justify throwing an error that would require manual intervention
 * to get the database running again.
 *
 * Returns true if successful, false if some subdirectory is not empty
 */
static bool
destroy_tablespace_directories(Oid tablespaceoid, bool redo)
{
    char       *linkloc;
    char       *linkloc_with_version_dir;
    DIR        *dirdesc;
    struct dirent *de;
    char       *subfile;
    struct stat st;
 
    linkloc_with_version_dir = psprintf("pg_tblspc/%u/%s", tablespaceoid,
                                        TABLESPACE_VERSION_DIRECTORY);
 
    /*
     * Check if the tablespace still contains any files.  We try to rmdir each
     * per-database directory we find in it.  rmdir failure implies there are
     * still files in that subdirectory, so give up.  (We do not have to worry
     * about undoing any already completed rmdirs, since the next attempt to
     * use the tablespace from that database will simply recreate the
     * subdirectory via TablespaceCreateDbspace.)
     *
     * Since we hold TablespaceCreateLock, no one else should be creating any
     * fresh subdirectories in parallel. It is possible that new files are
     * being created within subdirectories, though, so the rmdir call could
     * fail.  Worst consequence is a less friendly error message.
     *
     * If redo is true then ENOENT is a likely outcome here, and we allow it
     * to pass without comment.  In normal operation we still allow it, but
     * with a warning.  This is because even though ProcessUtility disallows
     * DROP TABLESPACE in a transaction block, it's possible that a previous
     * DROP failed and rolled back after removing the tablespace directories
     * and/or symlink.  We want to allow a new DROP attempt to succeed at
     * removing the catalog entries (and symlink if still present), so we
     * should not give a hard error here.
     */
    dirdesc = AllocateDir(linkloc_with_version_dir);
    if (dirdesc == NULL)
    {
        if (errno == ENOENT)
        {
            if (!redo)
                ereport(WARNING,
                        (errcode_for_file_access(),
                         errmsg("could not open directory \"%s\": %m",
                                linkloc_with_version_dir)));
            /* The symlink might still exist, so go try to remove it */
            goto remove_symlink;
        }
        else if (redo)
        {
            /* in redo, just log other types of error */
            ereport(LOG,
                    (errcode_for_file_access(),
                     errmsg("could not open directory \"%s\": %m",
                            linkloc_with_version_dir)));
            pfree(linkloc_with_version_dir);
            return false;
        }
        /* else let ReadDir report the error */
    }
 
    while ((de = ReadDir(dirdesc, linkloc_with_version_dir)) != NULL)
    {
        if (strcmp(de->d_name, ".") == 0 ||
            strcmp(de->d_name, "..") == 0)
            continue;
 
        subfile = psprintf("%s/%s", linkloc_with_version_dir, de->d_name);
 
        /* This check is just to deliver a friendlier error message */
        if (!redo && !directory_is_empty(subfile))
        {
            FreeDir(dirdesc);
            pfree(subfile);
            pfree(linkloc_with_version_dir);
            return false;
        }
 
        /* remove empty directory */
        if (rmdir(subfile) < 0)
            ereport(redo ? LOG : ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not remove directory \"%s\": %m",
                            subfile)));
 
        pfree(subfile);
    }
 
    FreeDir(dirdesc);
 
    /* remove version directory */
    if (rmdir(linkloc_with_version_dir) < 0)
    {
        ereport(redo ? LOG : ERROR,
                (errcode_for_file_access(),
                 errmsg("could not remove directory \"%s\": %m",
                        linkloc_with_version_dir)));
        pfree(linkloc_with_version_dir);
        return false;
    }
 
    /*
     * Try to remove the symlink.  We must however deal with the possibility
     * that it's a directory instead of a symlink --- this could happen during
     * WAL replay (see TablespaceCreateDbspace).
     *
     * Note: in the redo case, we'll return true if this final step fails;
     * there's no point in retrying it.  Also, ENOENT should provoke no more
     * than a warning.
     */
remove_symlink:
    linkloc = pstrdup(linkloc_with_version_dir);
    get_parent_directory(linkloc);
    if (lstat(linkloc, &st) < 0)
    {
        int         saved_errno = errno;
 
        ereport(redo ? LOG : (saved_errno == ENOENT ? WARNING : ERROR),
                (errcode_for_file_access(),
                 errmsg("could not stat file \"%s\": %m",
                        linkloc)));
    }
    else if (S_ISDIR(st.st_mode))
    {
        if (rmdir(linkloc) < 0)
        {
            int         saved_errno = errno;
 
            ereport(redo ? LOG : (saved_errno == ENOENT ? WARNING : ERROR),
                    (errcode_for_file_access(),
                     errmsg("could not remove directory \"%s\": %m",
                            linkloc)));
        }
    }
    else if (S_ISLNK(st.st_mode))
    {
        if (unlink(linkloc) < 0)
        {
            int         saved_errno = errno;
 
            ereport(redo ? LOG : (saved_errno == ENOENT ? WARNING : ERROR),
                    (errcode_for_file_access(),
                     errmsg("could not remove symbolic link \"%s\": %m",
                            linkloc)));
        }
    }
    else
    {
        /* Refuse to remove anything that's not a directory or symlink */
        ereport(redo ? LOG : ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("\"%s\" is not a directory or symbolic link",
                        linkloc)));
    }
 
    pfree(linkloc_with_version_dir);
    pfree(linkloc);
 
    return true;
}
 
 
/*
 * Check if a directory is empty.
 *
 * This probably belongs somewhere else, but not sure where...
 */
bool
directory_is_empty(const char *path)
{
    DIR        *dirdesc;
    struct dirent *de;
 
    dirdesc = AllocateDir(path);
 
    while ((de = ReadDir(dirdesc, path)) != NULL)
    {
        if (strcmp(de->d_name, ".") == 0 ||
            strcmp(de->d_name, "..") == 0)
            continue;
        FreeDir(dirdesc);
        return false;
    }
 
    FreeDir(dirdesc);
    return true;
}
 
/*
 *  remove_tablespace_symlink
 *
 * This function removes symlinks in pg_tblspc.  On Windows, junction points
 * act like directories so we must be able to apply rmdir.  This function
 * works like the symlink removal code in destroy_tablespace_directories,
 * except that failure to remove is always an ERROR.  But if the file doesn't
 * exist at all, that's OK.
 */
void
remove_tablespace_symlink(const char *linkloc)
{
    struct stat st;
 
    if (lstat(linkloc, &st) < 0)
    {
        if (errno == ENOENT)
            return;
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not stat file \"%s\": %m", linkloc)));
    }
 
    if (S_ISDIR(st.st_mode))
    {
        /*
         * This will fail if the directory isn't empty, but not if it's a
         * junction point.
         */
        if (rmdir(linkloc) < 0 && errno != ENOENT)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not remove directory \"%s\": %m",
                            linkloc)));
    }
    else if (S_ISLNK(st.st_mode))
    {
        if (unlink(linkloc) < 0 && errno != ENOENT)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not remove symbolic link \"%s\": %m",
                            linkloc)));
    }
    else
    {
        /* Refuse to remove anything that's not a directory or symlink */
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("\"%s\" is not a directory or symbolic link",
                        linkloc)));
    }
}
 
/*
 * Rename a tablespace
 */
ObjectAddress
RenameTableSpace(const char *oldname, const char *newname)
{
    Oid         tspId;
    Relation    rel;
    ScanKeyData entry[1];
    TableScanDesc scan;
    HeapTuple   tup;
    HeapTuple   newtuple;
    Form_pg_tablespace newform;
    ObjectAddress address;
 
    /* Search pg_tablespace */
    rel = table_open(TableSpaceRelationId, RowExclusiveLock);
 
    ScanKeyInit(&entry[0],
                Anum_pg_tablespace_spcname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(oldname));
    scan = table_beginscan_catalog(rel, 1, entry);
    tup = heap_getnext(scan, ForwardScanDirection);
    if (!HeapTupleIsValid(tup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("tablespace \"%s\" does not exist",
                        oldname)));
 
    newtuple = heap_copytuple(tup);
    newform = (Form_pg_tablespace) GETSTRUCT(newtuple);
    tspId = newform->oid;
 
    table_endscan(scan);
 
    /* Must be owner */
    if (!object_ownercheck(TableSpaceRelationId, tspId, GetUserId()))
        aclcheck_error(ACLCHECK_NO_PRIV, OBJECT_TABLESPACE, oldname);
 
    /* Validate new name */
    if (!allowSystemTableMods && IsReservedName(newname))
        ereport(ERROR,
                (errcode(ERRCODE_RESERVED_NAME),
                 errmsg("unacceptable tablespace name \"%s\"", newname),
                 errdetail("The prefix \"pg_\" is reserved for system tablespaces.")));
 
    /*
     * If built with appropriate switch, whine when regression-testing
     * conventions for tablespace names are violated.
     */
#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS
    if (strncmp(newname, "regress_", 8) != 0)
        elog(WARNING, "tablespaces created by regression test cases should have names starting with \"regress_\"");
#endif
 
    /* Make sure the new name doesn't exist */
    ScanKeyInit(&entry[0],
                Anum_pg_tablespace_spcname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(newname));
    scan = table_beginscan_catalog(rel, 1, entry);
    tup = heap_getnext(scan, ForwardScanDirection);
    if (HeapTupleIsValid(tup))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("tablespace \"%s\" already exists",
                        newname)));
 
    table_endscan(scan);
 
    /* OK, update the entry */
    namestrcpy(&(newform->spcname), newname);
 
    CatalogTupleUpdate(rel, &newtuple->t_self, newtuple);
 
    InvokeObjectPostAlterHook(TableSpaceRelationId, tspId, 0);
 
    ObjectAddressSet(address, TableSpaceRelationId, tspId);
 
    table_close(rel, NoLock);
 
    return address;
}
 
/*
 * Alter table space options
 */
Oid
AlterTableSpaceOptions(AlterTableSpaceOptionsStmt *stmt)
{
    Relation    rel;
    ScanKeyData entry[1];
    TableScanDesc scandesc;
    HeapTuple   tup;
    Oid         tablespaceoid;
    Datum       datum;
    Datum       newOptions;
    Datum       repl_val[Natts_pg_tablespace];
    bool        isnull;
    bool        repl_null[Natts_pg_tablespace];
    bool        repl_repl[Natts_pg_tablespace];
    HeapTuple   newtuple;
 
    /* Search pg_tablespace */
    rel = table_open(TableSpaceRelationId, RowExclusiveLock);
 
    ScanKeyInit(&entry[0],
                Anum_pg_tablespace_spcname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(stmt->tablespacename));
    scandesc = table_beginscan_catalog(rel, 1, entry);
    tup = heap_getnext(scandesc, ForwardScanDirection);
    if (!HeapTupleIsValid(tup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("tablespace \"%s\" does not exist",
                        stmt->tablespacename)));
 
    tablespaceoid = ((Form_pg_tablespace) GETSTRUCT(tup))->oid;
 
    /* Must be owner of the existing object */
    if (!object_ownercheck(TableSpaceRelationId, tablespaceoid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_TABLESPACE,
                       stmt->tablespacename);
 
    /* Generate new proposed spcoptions (text array) */
    datum = heap_getattr(tup, Anum_pg_tablespace_spcoptions,
                         RelationGetDescr(rel), &isnull);
    newOptions = transformRelOptions(isnull ? (Datum) 0 : datum,
                                     stmt->options, NULL, NULL, false,
                                     stmt->isReset);
    (void) tablespace_reloptions(newOptions, true);
 
    /* Build new tuple. */
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));
    if (newOptions != (Datum) 0)
        repl_val[Anum_pg_tablespace_spcoptions - 1] = newOptions;
    else
        repl_null[Anum_pg_tablespace_spcoptions - 1] = true;
    repl_repl[Anum_pg_tablespace_spcoptions - 1] = true;
    newtuple = heap_modify_tuple(tup, RelationGetDescr(rel), repl_val,
                                 repl_null, repl_repl);
 
    /* Update system catalog. */
    CatalogTupleUpdate(rel, &newtuple->t_self, newtuple);
 
    InvokeObjectPostAlterHook(TableSpaceRelationId, tablespaceoid, 0);
 
    heap_freetuple(newtuple);
 
    /* Conclude heap scan. */
    table_endscan(scandesc);
    table_close(rel, NoLock);
 
    return tablespaceoid;
}
 
/*
 * Routines for handling the GUC variable 'default_tablespace'.
 */
 
/* check_hook: validate new default_tablespace */
bool
check_default_tablespace(char **newval, void **extra, GucSource source)
{
    /*
     * If we aren't inside a transaction, or connected to a database, we
     * cannot do the catalog accesses necessary to verify the name.  Must
     * accept the value on faith.
     */
    if (IsTransactionState() && MyDatabaseId != InvalidOid)
    {
        if (**newval != '\0' &&
            !OidIsValid(get_tablespace_oid(*newval, true)))
        {
            /*
             * When source == PGC_S_TEST, don't throw a hard error for a
             * nonexistent tablespace, only a NOTICE.  See comments in guc.h.
             */
            if (source == PGC_S_TEST)
            {
                ereport(NOTICE,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("tablespace \"%s\" does not exist",
                                *newval)));
            }
            else
            {
                GUC_check_errdetail("Tablespace \"%s\" does not exist.",
                                    *newval);
                return false;
            }
        }
    }
 
    return true;
}
 
/*
 * GetDefaultTablespace -- get the OID of the current default tablespace
 *
 * Temporary objects have different default tablespaces, hence the
 * relpersistence parameter must be specified.  Also, for partitioned tables,
 * we disallow specifying the database default, so that needs to be specified
 * too.
 *
 * May return InvalidOid to indicate "use the database's default tablespace".
 *
 * Note that caller is expected to check appropriate permissions for any
 * result other than InvalidOid.
 *
 * This exists to hide (and possibly optimize the use of) the
 * default_tablespace GUC variable.
 */
Oid
GetDefaultTablespace(char relpersistence, bool partitioned)
{
    Oid         result;
 
    /* The temp-table case is handled elsewhere */
    if (relpersistence == RELPERSISTENCE_TEMP)
    {
        PrepareTempTablespaces();
        return GetNextTempTableSpace();
    }
 
    /* Fast path for default_tablespace == "" */
    if (default_tablespace == NULL || default_tablespace[0] == '\0')
        return InvalidOid;
 
    /*
     * It is tempting to cache this lookup for more speed, but then we would
     * fail to detect the case where the tablespace was dropped since the GUC
     * variable was set.  Note also that we don't complain if the value fails
     * to refer to an existing tablespace; we just silently return InvalidOid,
     * causing the new object to be created in the database's tablespace.
     */
    result = get_tablespace_oid(default_tablespace, true);
 
    /*
     * Allow explicit specification of database's default tablespace in
     * default_tablespace without triggering permissions checks.  Don't allow
     * specifying that when creating a partitioned table, however, since the
     * result is confusing.
     */
    if (result == MyDatabaseTableSpace)
    {
        if (partitioned)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cannot specify default tablespace for partitioned relations")));
        result = InvalidOid;
    }
    return result;
}
 
 
/*
 * Routines for handling the GUC variable 'temp_tablespaces'.
 */
 
typedef struct
{
    /* Array of OIDs to be passed to SetTempTablespaces() */
    int         numSpcs;
    Oid         tblSpcs[FLEXIBLE_ARRAY_MEMBER];
} temp_tablespaces_extra;
 
/* check_hook: validate new temp_tablespaces */
bool
check_temp_tablespaces(char **newval, void **extra, GucSource source)
{
    char       *rawname;
    List       *namelist;
 
    /* Need a modifiable copy of string */
    rawname = pstrdup(*newval);
 
    /* Parse string into list of identifiers */
    if (!SplitIdentifierString(rawname, ',', &namelist))
    {
        /* syntax error in name list */
        GUC_check_errdetail("List syntax is invalid.");
        pfree(rawname);
        list_free(namelist);
        return false;
    }
 
    /*
     * If we aren't inside a transaction, or connected to a database, we
     * cannot do the catalog accesses necessary to verify the name.  Must
     * accept the value on faith. Fortunately, there's then also no need to
     * pass the data to fd.c.
     */
    if (IsTransactionState() && MyDatabaseId != InvalidOid)
    {
        temp_tablespaces_extra *myextra;
        Oid        *tblSpcs;
        int         numSpcs;
        ListCell   *l;
 
        /* temporary workspace until we are done verifying the list */
        tblSpcs = (Oid *) palloc(list_length(namelist) * sizeof(Oid));
        numSpcs = 0;
        foreach(l, namelist)
        {
            char       *curname = (char *) lfirst(l);
            Oid         curoid;
            AclResult   aclresult;
 
            /* Allow an empty string (signifying database default) */
            if (curname[0] == '\0')
            {
                /* InvalidOid signifies database's default tablespace */
                tblSpcs[numSpcs++] = InvalidOid;
                continue;
            }
 
            /*
             * In an interactive SET command, we ereport for bad info.  When
             * source == PGC_S_TEST, don't throw a hard error for a
             * nonexistent tablespace, only a NOTICE.  See comments in guc.h.
             */
            curoid = get_tablespace_oid(curname, source <= PGC_S_TEST);
            if (curoid == InvalidOid)
            {
                if (source == PGC_S_TEST)
                    ereport(NOTICE,
                            (errcode(ERRCODE_UNDEFINED_OBJECT),
                             errmsg("tablespace \"%s\" does not exist",
                                    curname)));
                continue;
            }
 
            /*
             * Allow explicit specification of database's default tablespace
             * in temp_tablespaces without triggering permissions checks.
             */
            if (curoid == MyDatabaseTableSpace)
            {
                /* InvalidOid signifies database's default tablespace */
                tblSpcs[numSpcs++] = InvalidOid;
                continue;
            }
 
            /* Check permissions, similarly complaining only if interactive */
            aclresult = object_aclcheck(TableSpaceRelationId, curoid, GetUserId(),
                                               ACL_CREATE);
            if (aclresult != ACLCHECK_OK)
            {
                if (source >= PGC_S_INTERACTIVE)
                    aclcheck_error(aclresult, OBJECT_TABLESPACE, curname);
                continue;
            }
 
            tblSpcs[numSpcs++] = curoid;
        }
 
        /* Now prepare an "extra" struct for assign_temp_tablespaces */
        myextra = guc_malloc(LOG, offsetof(temp_tablespaces_extra, tblSpcs) +
                             numSpcs * sizeof(Oid));
        if (!myextra)
            return false;
        myextra->numSpcs = numSpcs;
        memcpy(myextra->tblSpcs, tblSpcs, numSpcs * sizeof(Oid));
        *extra = (void *) myextra;
 
        pfree(tblSpcs);
    }
 
    pfree(rawname);
    list_free(namelist);
 
    return true;
}
 
/* assign_hook: do extra actions as needed */
void
assign_temp_tablespaces(const char *newval, void *extra)
{
    temp_tablespaces_extra *myextra = (temp_tablespaces_extra *) extra;
 
    /*
     * If check_temp_tablespaces was executed inside a transaction, then pass
     * the list it made to fd.c.  Otherwise, clear fd.c's list; we must be
     * still outside a transaction, or else restoring during transaction exit,
     * and in either case we can just let the next PrepareTempTablespaces call
     * make things sane.
     */
    if (myextra)
        SetTempTablespaces(myextra->tblSpcs, myextra->numSpcs);
    else
        SetTempTablespaces(NULL, 0);
}
 
/*
 * PrepareTempTablespaces -- prepare to use temp tablespaces
 *
 * If we have not already done so in the current transaction, parse the
 * temp_tablespaces GUC variable and tell fd.c which tablespace(s) to use
 * for temp files.
 */
void
PrepareTempTablespaces(void)
{
    char       *rawname;
    List       *namelist;
    Oid        *tblSpcs;
    int         numSpcs;
    ListCell   *l;
 
    /* No work if already done in current transaction */
    if (TempTablespacesAreSet())
        return;
 
    /*
     * Can't do catalog access unless within a transaction.  This is just a
     * safety check in case this function is called by low-level code that
     * could conceivably execute outside a transaction.  Note that in such a
     * scenario, fd.c will fall back to using the current database's default
     * tablespace, which should always be OK.
     */
    if (!IsTransactionState())
        return;
 
    /* Need a modifiable copy of string */
    rawname = pstrdup(temp_tablespaces);
 
    /* Parse string into list of identifiers */
    if (!SplitIdentifierString(rawname, ',', &namelist))
    {
        /* syntax error in name list */
        SetTempTablespaces(NULL, 0);
        pfree(rawname);
        list_free(namelist);
        return;
    }
 
    /* Store tablespace OIDs in an array in TopTransactionContext */
    tblSpcs = (Oid *) MemoryContextAlloc(TopTransactionContext,
                                         list_length(namelist) * sizeof(Oid));
    numSpcs = 0;
    foreach(l, namelist)
    {
        char       *curname = (char *) lfirst(l);
        Oid         curoid;
        AclResult   aclresult;
 
        /* Allow an empty string (signifying database default) */
        if (curname[0] == '\0')
        {
            /* InvalidOid signifies database's default tablespace */
            tblSpcs[numSpcs++] = InvalidOid;
            continue;
        }
 
        /* Else verify that name is a valid tablespace name */
        curoid = get_tablespace_oid(curname, true);
        if (curoid == InvalidOid)
        {
            /* Skip any bad list elements */
            continue;
        }
 
        /*
         * Allow explicit specification of database's default tablespace in
         * temp_tablespaces without triggering permissions checks.
         */
        if (curoid == MyDatabaseTableSpace)
        {
            /* InvalidOid signifies database's default tablespace */
            tblSpcs[numSpcs++] = InvalidOid;
            continue;
        }
 
        /* Check permissions similarly */
        aclresult = object_aclcheck(TableSpaceRelationId, curoid, GetUserId(),
                                           ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            continue;
 
        tblSpcs[numSpcs++] = curoid;
    }
 
    SetTempTablespaces(tblSpcs, numSpcs);
 
    pfree(rawname);
    list_free(namelist);
}
 
 
/*
 * get_tablespace_oid - given a tablespace name, look up the OID
 *
 * If missing_ok is false, throw an error if tablespace name not found.  If
 * true, just return InvalidOid.
 */
Oid
get_tablespace_oid(const char *tablespacename, bool missing_ok)
{
    Oid         result;
    Relation    rel;
    TableScanDesc scandesc;
    HeapTuple   tuple;
    ScanKeyData entry[1];
 
    /*
     * Search pg_tablespace.  We use a heapscan here even though there is an
     * index on name, on the theory that pg_tablespace will usually have just
     * a few entries and so an indexed lookup is a waste of effort.
     */
    rel = table_open(TableSpaceRelationId, AccessShareLock);
 
    ScanKeyInit(&entry[0],
                Anum_pg_tablespace_spcname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(tablespacename));
    scandesc = table_beginscan_catalog(rel, 1, entry);
    tuple = heap_getnext(scandesc, ForwardScanDirection);
 
    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(tuple))
        result = ((Form_pg_tablespace) GETSTRUCT(tuple))->oid;
    else
        result = InvalidOid;
 
    table_endscan(scandesc);
    table_close(rel, AccessShareLock);
 
    if (!OidIsValid(result) && !missing_ok)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("tablespace \"%s\" does not exist",
                        tablespacename)));
 
    return result;
}
 
/*
 * get_tablespace_name - given a tablespace OID, look up the name
 *
 * Returns a palloc'd string, or NULL if no such tablespace.
 */
char *
get_tablespace_name(Oid spc_oid)
{
    char       *result;
    Relation    rel;
    TableScanDesc scandesc;
    HeapTuple   tuple;
    ScanKeyData entry[1];
 
    /*
     * Search pg_tablespace.  We use a heapscan here even though there is an
     * index on oid, on the theory that pg_tablespace will usually have just a
     * few entries and so an indexed lookup is a waste of effort.
     */
    rel = table_open(TableSpaceRelationId, AccessShareLock);
 
    ScanKeyInit(&entry[0],
                Anum_pg_tablespace_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(spc_oid));
    scandesc = table_beginscan_catalog(rel, 1, entry);
    tuple = heap_getnext(scandesc, ForwardScanDirection);
 
    /* We assume that there can be at most one matching tuple */
    if (HeapTupleIsValid(tuple))
        result = pstrdup(NameStr(((Form_pg_tablespace) GETSTRUCT(tuple))->spcname));
    else
        result = NULL;
 
    table_endscan(scandesc);
    table_close(rel, AccessShareLock);
 
    return result;
}
 
 
/*
 * TABLESPACE resource manager's routines
 */
void
tblspc_redo(XLogReaderState *record)
{
    uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
 
    /* Backup blocks are not used in tblspc records */
    Assert(!XLogRecHasAnyBlockRefs(record));
 
    if (info == XLOG_TBLSPC_CREATE)
    {
        xl_tblspc_create_rec *xlrec = (xl_tblspc_create_rec *) XLogRecGetData(record);
        char       *location = xlrec->ts_path;
 
        create_tablespace_directories(location, xlrec->ts_id);
    }
    else if (info == XLOG_TBLSPC_DROP)
    {
        xl_tblspc_drop_rec *xlrec = (xl_tblspc_drop_rec *) XLogRecGetData(record);
 
        /* Close all smgr fds in all backends. */
        WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
 
        /*
         * If we issued a WAL record for a drop tablespace it implies that
         * there were no files in it at all when the DROP was done. That means
         * that no permanent objects can exist in it at this point.
         *
         * It is possible for standby users to be using this tablespace as a
         * location for their temporary files, so if we fail to remove all
         * files then do conflict processing and try again, if currently
         * enabled.
         *
         * Other possible reasons for failure include bollixed file
         * permissions on a standby server when they were okay on the primary,
         * etc etc. There's not much we can do about that, so just remove what
         * we can and press on.
         */
        if (!destroy_tablespace_directories(xlrec->ts_id, true))
        {
            ResolveRecoveryConflictWithTablespace(xlrec->ts_id);
 
            /*
             * If we did recovery processing then hopefully the backends who
             * wrote temp files should have cleaned up and exited by now.  So
             * retry before complaining.  If we fail again, this is just a LOG
             * condition, because it's not worth throwing an ERROR for (as
             * that would crash the database and require manual intervention
             * before we could get past this WAL record on restart).
             */
            if (!destroy_tablespace_directories(xlrec->ts_id, true))
                ereport(LOG,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("directories for tablespace %u could not be removed",
                                xlrec->ts_id),
                         errhint("You can remove the directories manually if necessary.")));
        }
    }
    else
        elog(PANIC, "tblspc_redo: unknown op code %u", info);
}