postinit.c

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/*-------------------------------------------------------------------------
 *
 * postinit.c
 *    postgres initialization utilities
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/init/postinit.c
 *
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <ctype.h>
#include <fcntl.h>
#include <unistd.h>

#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/session.h"
#include "access/sysattr.h"
#include "access/tableam.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/catalog.h"
#include "catalog/namespace.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_database.h"
#include "catalog/pg_db_role_setting.h"
#include "catalog/pg_tablespace.h"
#include "libpq/auth.h"
#include "libpq/libpq-be.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "postmaster/postmaster.h"
#include "replication/walsender.h"
#include "storage/bufmgr.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/procsignal.h"
#include "storage/sinvaladt.h"
#include "storage/smgr.h"
#include "storage/sync.h"
#include "tcop/tcopprot.h"
#include "utils/acl.h"
#include "utils/fmgroids.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/pg_locale.h"
#include "utils/portal.h"
#include "utils/ps_status.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/timeout.h"

static HeapTuple GetDatabaseTuple(const char *dbname);
static HeapTuple GetDatabaseTupleByOid(Oid dboid);
static void PerformAuthentication(Port *port);
static void CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connections);
static void ShutdownPostgres(int code, Datum arg);
static void StatementTimeoutHandler(void);
static void LockTimeoutHandler(void);
static void IdleInTransactionSessionTimeoutHandler(void);
static void IdleSessionTimeoutHandler(void);
static void ClientCheckTimeoutHandler(void);
static bool ThereIsAtLeastOneRole(void);
static void process_startup_options(Port *port, bool am_superuser);
static void process_settings(Oid databaseid, Oid roleid);


/*** InitPostgres support ***/


/*
 * GetDatabaseTuple -- fetch the pg_database row for a database
 *
 * This is used during backend startup when we don't yet have any access to
 * system catalogs in general.  In the worst case, we can seqscan pg_database
 * using nothing but the hard-wired descriptor that relcache.c creates for
 * pg_database.  In more typical cases, relcache.c was able to load
 * descriptors for both pg_database and its indexes from the shared relcache
 * cache file, and so we can do an indexscan.  criticalSharedRelcachesBuilt
 * tells whether we got the cached descriptors.
 */
static HeapTuple
GetDatabaseTuple(const char *dbname)
{
    HeapTuple   tuple;
    Relation    relation;
    SysScanDesc scan;
    ScanKeyData key[1];

    /*
     * form a scan key
     */
    ScanKeyInit(&key[0],
                Anum_pg_database_datname,
                BTEqualStrategyNumber, F_NAMEEQ,
                CStringGetDatum(dbname));

    /*
     * Open pg_database and fetch a tuple.  Force heap scan if we haven't yet
     * built the critical shared relcache entries (i.e., we're starting up
     * without a shared relcache cache file).
     */
    relation = table_open(DatabaseRelationId, AccessShareLock);
    scan = systable_beginscan(relation, DatabaseNameIndexId,
                              criticalSharedRelcachesBuilt,
                              NULL,
                              1, key);

    tuple = systable_getnext(scan);

    /* Must copy tuple before releasing buffer */
    if (HeapTupleIsValid(tuple))
        tuple = heap_copytuple(tuple);

    /* all done */
    systable_endscan(scan);
    table_close(relation, AccessShareLock);

    return tuple;
}

/*
 * GetDatabaseTupleByOid -- as above, but search by database OID
 */
static HeapTuple
GetDatabaseTupleByOid(Oid dboid)
{
    HeapTuple   tuple;
    Relation    relation;
    SysScanDesc scan;
    ScanKeyData key[1];

    /*
     * form a scan key
     */
    ScanKeyInit(&key[0],
                Anum_pg_database_oid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(dboid));

    /*
     * Open pg_database and fetch a tuple.  Force heap scan if we haven't yet
     * built the critical shared relcache entries (i.e., we're starting up
     * without a shared relcache cache file).
     */
    relation = table_open(DatabaseRelationId, AccessShareLock);
    scan = systable_beginscan(relation, DatabaseOidIndexId,
                              criticalSharedRelcachesBuilt,
                              NULL,
                              1, key);

    tuple = systable_getnext(scan);

    /* Must copy tuple before releasing buffer */
    if (HeapTupleIsValid(tuple))
        tuple = heap_copytuple(tuple);

    /* all done */
    systable_endscan(scan);
    table_close(relation, AccessShareLock);

    return tuple;
}


/*
 * PerformAuthentication -- authenticate a remote client
 *
 * returns: nothing.  Will not return at all if there's any failure.
 */
static void
PerformAuthentication(Port *port)
{
    /* This should be set already, but let's make sure */
    ClientAuthInProgress = true;    /* limit visibility of log messages */

    /*
     * In EXEC_BACKEND case, we didn't inherit the contents of pg_hba.conf
     * etcetera from the postmaster, and have to load them ourselves.
     *
     * FIXME: [fork/exec] Ugh.  Is there a way around this overhead?
     */
#ifdef EXEC_BACKEND

    /*
     * load_hba() and load_ident() want to work within the PostmasterContext,
     * so create that if it doesn't exist (which it won't).  We'll delete it
     * again later, in PostgresMain.
     */
    if (PostmasterContext == NULL)
        PostmasterContext = AllocSetContextCreate(TopMemoryContext,
                                                  "Postmaster",
                                                  ALLOCSET_DEFAULT_SIZES);

    if (!load_hba())
    {
        /*
         * It makes no sense to continue if we fail to load the HBA file,
         * since there is no way to connect to the database in this case.
         */
        ereport(FATAL,
                (errmsg("could not load pg_hba.conf")));
    }

    if (!load_ident())
    {
        /*
         * It is ok to continue if we fail to load the IDENT file, although it
         * means that you cannot log in using any of the authentication
         * methods that need a user name mapping. load_ident() already logged
         * the details of error to the log.
         */
    }
#endif

    /*
     * Set up a timeout in case a buggy or malicious client fails to respond
     * during authentication.  Since we're inside a transaction and might do
     * database access, we have to use the statement_timeout infrastructure.
     */
    enable_timeout_after(STATEMENT_TIMEOUT, AuthenticationTimeout * 1000);

    /*
     * Now perform authentication exchange.
     */
    set_ps_display("authentication");
    ClientAuthentication(port); /* might not return, if failure */

    /*
     * Done with authentication.  Disable the timeout, and log if needed.
     */
    disable_timeout(STATEMENT_TIMEOUT, false);

    if (Log_connections)
    {
        StringInfoData logmsg;

        initStringInfo(&logmsg);
        if (am_walsender)
            appendStringInfo(&logmsg, _("replication connection authorized: user=%s"),
                             port->user_name);
        else
            appendStringInfo(&logmsg, _("connection authorized: user=%s"),
                             port->user_name);
        if (!am_walsender)
            appendStringInfo(&logmsg, _(" database=%s"), port->database_name);

        if (port->application_name != NULL)
            appendStringInfo(&logmsg, _(" application_name=%s"),
                             port->application_name);

#ifdef USE_SSL
        if (port->ssl_in_use)
            appendStringInfo(&logmsg, _(" SSL enabled (protocol=%s, cipher=%s, bits=%d)"),
                             be_tls_get_version(port),
                             be_tls_get_cipher(port),
                             be_tls_get_cipher_bits(port));
#endif
#ifdef ENABLE_GSS
        if (port->gss)
        {
            const char *princ = be_gssapi_get_princ(port);

            if (princ)
                appendStringInfo(&logmsg,
                                 _(" GSS (authenticated=%s, encrypted=%s, principal=%s)"),
                                 be_gssapi_get_auth(port) ? _("yes") : _("no"),
                                 be_gssapi_get_enc(port) ? _("yes") : _("no"),
                                 princ);
            else
                appendStringInfo(&logmsg,
                                 _(" GSS (authenticated=%s, encrypted=%s)"),
                                 be_gssapi_get_auth(port) ? _("yes") : _("no"),
                                 be_gssapi_get_enc(port) ? _("yes") : _("no"));
        }
#endif

        ereport(LOG, errmsg_internal("%s", logmsg.data));
        pfree(logmsg.data);
    }

    set_ps_display("startup");

    ClientAuthInProgress = false;   /* client_min_messages is active now */
}


/*
 * CheckMyDatabase -- fetch information from the pg_database entry for our DB
 */
static void
CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connections)
{
    HeapTuple   tup;
    Form_pg_database dbform;
    char       *collate;
    char       *ctype;

    /* Fetch our pg_database row normally, via syscache */
    tup = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
    if (!HeapTupleIsValid(tup))
        elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
    dbform = (Form_pg_database) GETSTRUCT(tup);

    /* This recheck is strictly paranoia */
    if (strcmp(name, NameStr(dbform->datname)) != 0)
        ereport(FATAL,
                (errcode(ERRCODE_UNDEFINED_DATABASE),
                 errmsg("database \"%s\" has disappeared from pg_database",
                        name),
                 errdetail("Database OID %u now seems to belong to \"%s\".",
                           MyDatabaseId, NameStr(dbform->datname))));

    /*
     * Check permissions to connect to the database.
     *
     * These checks are not enforced when in standalone mode, so that there is
     * a way to recover from disabling all access to all databases, for
     * example "UPDATE pg_database SET datallowconn = false;".
     *
     * We do not enforce them for autovacuum worker processes either.
     */
    if (IsUnderPostmaster && !IsAutoVacuumWorkerProcess())
    {
        /*
         * Check that the database is currently allowing connections.
         */
        if (!dbform->datallowconn && !override_allow_connections)
            ereport(FATAL,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("database \"%s\" is not currently accepting connections",
                            name)));

        /*
         * Check privilege to connect to the database.  (The am_superuser test
         * is redundant, but since we have the flag, might as well check it
         * and save a few cycles.)
         */
        if (!am_superuser &&
            pg_database_aclcheck(MyDatabaseId, GetUserId(),
                                 ACL_CONNECT) != ACLCHECK_OK)
            ereport(FATAL,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("permission denied for database \"%s\"", name),
                     errdetail("User does not have CONNECT privilege.")));

        /*
         * Check connection limit for this database.
         *
         * There is a race condition here --- we create our PGPROC before
         * checking for other PGPROCs.  If two backends did this at about the
         * same time, they might both think they were over the limit, while
         * ideally one should succeed and one fail.  Getting that to work
         * exactly seems more trouble than it is worth, however; instead we
         * just document that the connection limit is approximate.
         */
        if (dbform->datconnlimit >= 0 &&
            !am_superuser &&
            CountDBConnections(MyDatabaseId) > dbform->datconnlimit)
            ereport(FATAL,
                    (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                     errmsg("too many connections for database \"%s\"",
                            name)));
    }

    /*
     * OK, we're golden.  Next to-do item is to save the encoding info out of
     * the pg_database tuple.
     */
    SetDatabaseEncoding(dbform->encoding);
    /* Record it as a GUC internal option, too */
    SetConfigOption("server_encoding", GetDatabaseEncodingName(),
                    PGC_INTERNAL, PGC_S_OVERRIDE);
    /* If we have no other source of client_encoding, use server encoding */
    SetConfigOption("client_encoding", GetDatabaseEncodingName(),
                    PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);

    /* assign locale variables */
    collate = NameStr(dbform->datcollate);
    ctype = NameStr(dbform->datctype);

    if (pg_perm_setlocale(LC_COLLATE, collate) == NULL)
        ereport(FATAL,
                (errmsg("database locale is incompatible with operating system"),
                 errdetail("The database was initialized with LC_COLLATE \"%s\", "
                           " which is not recognized by setlocale().", collate),
                 errhint("Recreate the database with another locale or install the missing locale.")));

    if (pg_perm_setlocale(LC_CTYPE, ctype) == NULL)
        ereport(FATAL,
                (errmsg("database locale is incompatible with operating system"),
                 errdetail("The database was initialized with LC_CTYPE \"%s\", "
                           " which is not recognized by setlocale().", ctype),
                 errhint("Recreate the database with another locale or install the missing locale.")));

    /* Make the locale settings visible as GUC variables, too */
    SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
    SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_OVERRIDE);

    check_strxfrm_bug();

    ReleaseSysCache(tup);
}


/*
 * pg_split_opts -- split a string of options and append it to an argv array
 *
 * The caller is responsible for ensuring the argv array is large enough.  The
 * maximum possible number of arguments added by this routine is
 * (strlen(optstr) + 1) / 2.
 *
 * Because some option values can contain spaces we allow escaping using
 * backslashes, with \\ representing a literal backslash.
 */
void
pg_split_opts(char **argv, int *argcp, const char *optstr)
{
    StringInfoData s;

    initStringInfo(&s);

    while (*optstr)
    {
        bool        last_was_escape = false;

        resetStringInfo(&s);

        /* skip over leading space */
        while (isspace((unsigned char) *optstr))
            optstr++;

        if (*optstr == '\0')
            break;

        /*
         * Parse a single option, stopping at the first space, unless it's
         * escaped.
         */
        while (*optstr)
        {
            if (isspace((unsigned char) *optstr) && !last_was_escape)
                break;

            if (!last_was_escape && *optstr == '\\')
                last_was_escape = true;
            else
            {
                last_was_escape = false;
                appendStringInfoChar(&s, *optstr);
            }

            optstr++;
        }

        /* now store the option in the next argv[] position */
        argv[(*argcp)++] = pstrdup(s.data);
    }

    pfree(s.data);
}

/*
 * Initialize MaxBackends value from config options.
 *
 * This must be called after modules have had the chance to register background
 * workers in shared_preload_libraries, and before shared memory size is
 * determined.
 *
 * Note that in EXEC_BACKEND environment, the value is passed down from
 * postmaster to subprocesses via BackendParameters in SubPostmasterMain; only
 * postmaster itself and processes not under postmaster control should call
 * this.
 */
void
InitializeMaxBackends(void)
{
    Assert(MaxBackends == 0);

    /* the extra unit accounts for the autovacuum launcher */
    MaxBackends = MaxConnections + autovacuum_max_workers + 1 +
        max_worker_processes + max_wal_senders;

    /* internal error because the values were all checked previously */
    if (MaxBackends > MAX_BACKENDS)
        elog(ERROR, "too many backends configured");
}

/*
 * Early initialization of a backend (either standalone or under postmaster).
 * This happens even before InitPostgres.
 *
 * This is separate from InitPostgres because it is also called by auxiliary
 * processes, such as the background writer process, which may not call
 * InitPostgres at all.
 */
void
BaseInit(void)
{
    Assert(MyProc != NULL);

    /*
     * Initialize our input/output/debugging file descriptors.
     */
    DebugFileOpen();

    /*
     * Initialize file access. Done early so other subsystems can access
     * files.
     */
    InitFileAccess();

    /*
     * Initialize statistics reporting. This needs to happen early to ensure
     * that pgstat's shutdown callback runs after the shutdown callbacks of
     * all subsystems that can produce stats (like e.g. transaction commits
     * can).
     */
    pgstat_initialize();

    /* Do local initialization of storage and buffer managers */
    InitSync();
    smgrinit();
    InitBufferPoolAccess();

    /*
     * Initialize temporary file access after pgstat, so that the temporary
     * file shutdown hook can report temporary file statistics.
     */
    InitTemporaryFileAccess();
}


/* --------------------------------
 * InitPostgres
 *      Initialize POSTGRES.
 *
 * The database can be specified by name, using the in_dbname parameter, or by
 * OID, using the dboid parameter.  In the latter case, the actual database
 * name can be returned to the caller in out_dbname.  If out_dbname isn't
 * NULL, it must point to a buffer of size NAMEDATALEN.
 *
 * Similarly, the username can be passed by name, using the username parameter,
 * or by OID using the useroid parameter.
 *
 * In bootstrap mode no parameters are used.  The autovacuum launcher process
 * doesn't use any parameters either, because it only goes far enough to be
 * able to read pg_database; it doesn't connect to any particular database.
 * In walsender mode only username is used.
 *
 * As of PostgreSQL 8.2, we expect InitProcess() was already called, so we
 * already have a PGPROC struct ... but it's not completely filled in yet.
 *
 * Note:
 *      Be very careful with the order of calls in the InitPostgres function.
 * --------------------------------
 */
void
InitPostgres(const char *in_dbname, Oid dboid, const char *username,
             Oid useroid, char *out_dbname, bool override_allow_connections)
{
    bool        bootstrap = IsBootstrapProcessingMode();
    bool        am_superuser;
    char       *fullpath;
    char        dbname[NAMEDATALEN];

    elog(DEBUG3, "InitPostgres");

    /*
     * Add my PGPROC struct to the ProcArray.
     *
     * Once I have done this, I am visible to other backends!
     */
    InitProcessPhase2();

    /*
     * Initialize my entry in the shared-invalidation manager's array of
     * per-backend data.
     *
     * Sets up MyBackendId, a unique backend identifier.
     */
    MyBackendId = InvalidBackendId;

    SharedInvalBackendInit(false);

    if (MyBackendId > MaxBackends || MyBackendId <= 0)
        elog(FATAL, "bad backend ID: %d", MyBackendId);

    /* Now that we have a BackendId, we can participate in ProcSignal */
    ProcSignalInit(MyBackendId);

    /*
     * Also set up timeout handlers needed for backend operation.  We need
     * these in every case except bootstrap.
     */
    if (!bootstrap)
    {
        RegisterTimeout(DEADLOCK_TIMEOUT, CheckDeadLockAlert);
        RegisterTimeout(STATEMENT_TIMEOUT, StatementTimeoutHandler);
        RegisterTimeout(LOCK_TIMEOUT, LockTimeoutHandler);
        RegisterTimeout(IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
                        IdleInTransactionSessionTimeoutHandler);
        RegisterTimeout(IDLE_SESSION_TIMEOUT, IdleSessionTimeoutHandler);
        RegisterTimeout(CLIENT_CONNECTION_CHECK_TIMEOUT, ClientCheckTimeoutHandler);
    }

    /*
     * Initialize local process's access to XLOG.
     */
    if (IsUnderPostmaster)
    {
        /*
         * The postmaster already started the XLOG machinery, but we need to
         * call InitXLOGAccess(), if the system isn't in hot-standby mode.
         * This is handled by calling RecoveryInProgress and ignoring the
         * result.
         */
        (void) RecoveryInProgress();
    }
    else
    {
        /*
         * We are either a bootstrap process or a standalone backend. Either
         * way, start up the XLOG machinery, and register to have it closed
         * down at exit.
         *
         * We don't yet have an aux-process resource owner, but StartupXLOG
         * and ShutdownXLOG will need one.  Hence, create said resource owner
         * (and register a callback to clean it up after ShutdownXLOG runs).
         */
        CreateAuxProcessResourceOwner();

        StartupXLOG();
        /* Release (and warn about) any buffer pins leaked in StartupXLOG */
        ReleaseAuxProcessResources(true);
        /* Reset CurrentResourceOwner to nothing for the moment */
        CurrentResourceOwner = NULL;

        /*
         * Use before_shmem_exit() so that ShutdownXLOG() can rely on DSM
         * segments etc to work (which in turn is required for pgstats).
         */
        before_shmem_exit(ShutdownXLOG, 0);
    }

    /*
     * Initialize the relation cache and the system catalog caches.  Note that
     * no catalog access happens here; we only set up the hashtable structure.
     * We must do this before starting a transaction because transaction abort
     * would try to touch these hashtables.
     */
    RelationCacheInitialize();
    InitCatalogCache();
    InitPlanCache();

    /* Initialize portal manager */
    EnablePortalManager();

    /* Initialize status reporting */
    if (!bootstrap)
        pgstat_beinit();

    /*
     * Load relcache entries for the shared system catalogs.  This must create
     * at least entries for pg_database and catalogs used for authentication.
     */
    RelationCacheInitializePhase2();

    /*
     * Set up process-exit callback to do pre-shutdown cleanup.  This is the
     * one of the first before_shmem_exit callbacks we register; thus, this
     * will be one the last things we do before low-level modules like the
     * buffer manager begin to close down.  We need to have this in place
     * before we begin our first transaction --- if we fail during the
     * initialization transaction, as is entirely possible, we need the
     * AbortTransaction call to clean up.
     */
    before_shmem_exit(ShutdownPostgres, 0);

    /* The autovacuum launcher is done here */
    if (IsAutoVacuumLauncherProcess())
    {
        /* report this backend in the PgBackendStatus array */
        pgstat_bestart();

        return;
    }

    /*
     * Start a new transaction here before first access to db, and get a
     * snapshot.  We don't have a use for the snapshot itself, but we're
     * interested in the secondary effect that it sets RecentGlobalXmin. (This
     * is critical for anything that reads heap pages, because HOT may decide
     * to prune them even if the process doesn't attempt to modify any
     * tuples.)
     *
     * FIXME: This comment is inaccurate / the code buggy. A snapshot that is
     * not pushed/active does not reliably prevent HOT pruning (->xmin could
     * e.g. be cleared when cache invalidations are processed).
     */
    if (!bootstrap)
    {
        /* statement_timestamp must be set for timeouts to work correctly */
        SetCurrentStatementStartTimestamp();
        StartTransactionCommand();

        /*
         * transaction_isolation will have been set to the default by the
         * above.  If the default is "serializable", and we are in hot
         * standby, we will fail if we don't change it to something lower.
         * Fortunately, "read committed" is plenty good enough.
         */
        XactIsoLevel = XACT_READ_COMMITTED;

        (void) GetTransactionSnapshot();
    }

    /*
     * Perform client authentication if necessary, then figure out our
     * postgres user ID, and see if we are a superuser.
     *
     * In standalone mode and in autovacuum worker processes, we use a fixed
     * ID, otherwise we figure it out from the authenticated user name.
     */
    if (bootstrap || IsAutoVacuumWorkerProcess())
    {
        InitializeSessionUserIdStandalone();
        am_superuser = true;
    }
    else if (!IsUnderPostmaster)
    {
        InitializeSessionUserIdStandalone();
        am_superuser = true;
        if (!ThereIsAtLeastOneRole())
            ereport(WARNING,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("no roles are defined in this database system"),
                     errhint("You should immediately run CREATE USER \"%s\" SUPERUSER;.",
                             username != NULL ? username : "postgres")));
    }
    else if (IsBackgroundWorker)
    {
        if (username == NULL && !OidIsValid(useroid))
        {
            InitializeSessionUserIdStandalone();
            am_superuser = true;
        }
        else
        {
            InitializeSessionUserId(username, useroid);
            am_superuser = superuser();
        }
    }
    else
    {
        /* normal multiuser case */
        Assert(MyProcPort != NULL);
        PerformAuthentication(MyProcPort);
        InitializeSessionUserId(username, useroid);
        am_superuser = superuser();
    }

    /*
     * If we're trying to shut down, only superusers can connect, and new
     * replication connections are not allowed.
     */
    if ((!am_superuser || am_walsender) &&
        MyProcPort != NULL &&
        MyProcPort->canAcceptConnections == CAC_SUPERUSER)
    {
        if (am_walsender)
            ereport(FATAL,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("new replication connections are not allowed during database shutdown")));
        else
            ereport(FATAL,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("must be superuser to connect during database shutdown")));
    }

    /*
     * Binary upgrades only allowed super-user connections
     */
    if (IsBinaryUpgrade && !am_superuser)
    {
        ereport(FATAL,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to connect in binary upgrade mode")));
    }

    /*
     * The last few connection slots are reserved for superusers.  Replication
     * connections are drawn from slots reserved with max_wal_senders and not
     * limited by max_connections or superuser_reserved_connections.
     */
    if (!am_superuser && !am_walsender &&
        ReservedBackends > 0 &&
        !HaveNFreeProcs(ReservedBackends))
        ereport(FATAL,
                (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                 errmsg("remaining connection slots are reserved for non-replication superuser connections")));

    /* Check replication permissions needed for walsender processes. */
    if (am_walsender)
    {
        Assert(!bootstrap);

        if (!superuser() && !has_rolreplication(GetUserId()))
            ereport(FATAL,
                    (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                     errmsg("must be superuser or replication role to start walsender")));
    }

    /*
     * If this is a plain walsender only supporting physical replication, we
     * don't want to connect to any particular database. Just finish the
     * backend startup by processing any options from the startup packet, and
     * we're done.
     */
    if (am_walsender && !am_db_walsender)
    {
        /* process any options passed in the startup packet */
        if (MyProcPort != NULL)
            process_startup_options(MyProcPort, am_superuser);

        /* Apply PostAuthDelay as soon as we've read all options */
        if (PostAuthDelay > 0)
            pg_usleep(PostAuthDelay * 1000000L);

        /* initialize client encoding */
        InitializeClientEncoding();

        /* report this backend in the PgBackendStatus array */
        pgstat_bestart();

        /* close the transaction we started above */
        CommitTransactionCommand();

        return;
    }

    /*
     * Set up the global variables holding database id and default tablespace.
     * But note we won't actually try to touch the database just yet.
     *
     * We take a shortcut in the bootstrap case, otherwise we have to look up
     * the db's entry in pg_database.
     */
    if (bootstrap)
    {
        MyDatabaseId = TemplateDbOid;
        MyDatabaseTableSpace = DEFAULTTABLESPACE_OID;
    }
    else if (in_dbname != NULL)
    {
        HeapTuple   tuple;
        Form_pg_database dbform;

        tuple = GetDatabaseTuple(in_dbname);
        if (!HeapTupleIsValid(tuple))
            ereport(FATAL,
                    (errcode(ERRCODE_UNDEFINED_DATABASE),
                     errmsg("database \"%s\" does not exist", in_dbname)));
        dbform = (Form_pg_database) GETSTRUCT(tuple);
        MyDatabaseId = dbform->oid;
        MyDatabaseTableSpace = dbform->dattablespace;
        /* take database name from the caller, just for paranoia */
        strlcpy(dbname, in_dbname, sizeof(dbname));
    }
    else if (OidIsValid(dboid))
    {
        /* caller specified database by OID */
        HeapTuple   tuple;
        Form_pg_database dbform;

        tuple = GetDatabaseTupleByOid(dboid);
        if (!HeapTupleIsValid(tuple))
            ereport(FATAL,
                    (errcode(ERRCODE_UNDEFINED_DATABASE),
                     errmsg("database %u does not exist", dboid)));
        dbform = (Form_pg_database) GETSTRUCT(tuple);
        MyDatabaseId = dbform->oid;
        MyDatabaseTableSpace = dbform->dattablespace;
        Assert(MyDatabaseId == dboid);
        strlcpy(dbname, NameStr(dbform->datname), sizeof(dbname));
        /* pass the database name back to the caller */
        if (out_dbname)
            strcpy(out_dbname, dbname);
    }
    else
    {
        /*
         * If this is a background worker not bound to any particular
         * database, we're done now.  Everything that follows only makes sense
         * if we are bound to a specific database.  We do need to close the
         * transaction we started before returning.
         */
        if (!bootstrap)
        {
            pgstat_bestart();
            CommitTransactionCommand();
        }
        return;
    }

    /*
     * Now, take a writer's lock on the database we are trying to connect to.
     * If there is a concurrently running DROP DATABASE on that database, this
     * will block us until it finishes (and has committed its update of
     * pg_database).
     *
     * Note that the lock is not held long, only until the end of this startup
     * transaction.  This is OK since we will advertise our use of the
     * database in the ProcArray before dropping the lock (in fact, that's the
     * next thing to do).  Anyone trying a DROP DATABASE after this point will
     * see us in the array once they have the lock.  Ordering is important for
     * this because we don't want to advertise ourselves as being in this
     * database until we have the lock; otherwise we create what amounts to a
     * deadlock with CountOtherDBBackends().
     *
     * Note: use of RowExclusiveLock here is reasonable because we envision
     * our session as being a concurrent writer of the database.  If we had a
     * way of declaring a session as being guaranteed-read-only, we could use
     * AccessShareLock for such sessions and thereby not conflict against
     * CREATE DATABASE.
     */
    if (!bootstrap)
        LockSharedObject(DatabaseRelationId, MyDatabaseId, 0,
                         RowExclusiveLock);

    /*
     * Now we can mark our PGPROC entry with the database ID.
     *
     * We assume this is an atomic store so no lock is needed; though actually
     * things would work fine even if it weren't atomic.  Anyone searching the
     * ProcArray for this database's ID should hold the database lock, so they
     * would not be executing concurrently with this store.  A process looking
     * for another database's ID could in theory see a chance match if it read
     * a partially-updated databaseId value; but as long as all such searches
     * wait and retry, as in CountOtherDBBackends(), they will certainly see
     * the correct value on their next try.
     */
    MyProc->databaseId = MyDatabaseId;

    /*
     * We established a catalog snapshot while reading pg_authid and/or
     * pg_database; but until we have set up MyDatabaseId, we won't react to
     * incoming sinval messages for unshared catalogs, so we won't realize it
     * if the snapshot has been invalidated.  Assume it's no good anymore.
     */
    InvalidateCatalogSnapshot();

    /*
     * Recheck pg_database to make sure the target database hasn't gone away.
     * If there was a concurrent DROP DATABASE, this ensures we will die
     * cleanly without creating a mess.
     */
    if (!bootstrap)
    {
        HeapTuple   tuple;

        tuple = GetDatabaseTuple(dbname);
        if (!HeapTupleIsValid(tuple) ||
            MyDatabaseId != ((Form_pg_database) GETSTRUCT(tuple))->oid ||
            MyDatabaseTableSpace != ((Form_pg_database) GETSTRUCT(tuple))->dattablespace)
            ereport(FATAL,
                    (errcode(ERRCODE_UNDEFINED_DATABASE),
                     errmsg("database \"%s\" does not exist", dbname),
                     errdetail("It seems to have just been dropped or renamed.")));
    }

    /*
     * Now we should be able to access the database directory safely. Verify
     * it's there and looks reasonable.
     */
    fullpath = GetDatabasePath(MyDatabaseId, MyDatabaseTableSpace);

    if (!bootstrap)
    {
        if (access(fullpath, F_OK) == -1)
        {
            if (errno == ENOENT)
                ereport(FATAL,
                        (errcode(ERRCODE_UNDEFINED_DATABASE),
                         errmsg("database \"%s\" does not exist",
                                dbname),
                         errdetail("The database subdirectory \"%s\" is missing.",
                                   fullpath)));
            else
                ereport(FATAL,
                        (errcode_for_file_access(),
                         errmsg("could not access directory \"%s\": %m",
                                fullpath)));
        }

        ValidatePgVersion(fullpath);
    }

    SetDatabasePath(fullpath);

    /*
     * It's now possible to do real access to the system catalogs.
     *
     * Load relcache entries for the system catalogs.  This must create at
     * least the minimum set of "nailed-in" cache entries.
     */
    RelationCacheInitializePhase3();

    /* set up ACL framework (so CheckMyDatabase can check permissions) */
    initialize_acl();

    /*
     * Re-read the pg_database row for our database, check permissions and set
     * up database-specific GUC settings.  We can't do this until all the
     * database-access infrastructure is up.  (Also, it wants to know if the
     * user is a superuser, so the above stuff has to happen first.)
     */
    if (!bootstrap)
        CheckMyDatabase(dbname, am_superuser, override_allow_connections);

    /*
     * Now process any command-line switches and any additional GUC variable
     * settings passed in the startup packet.   We couldn't do this before
     * because we didn't know if client is a superuser.
     */
    if (MyProcPort != NULL)
        process_startup_options(MyProcPort, am_superuser);

    /* Process pg_db_role_setting options */
    process_settings(MyDatabaseId, GetSessionUserId());

    /* Apply PostAuthDelay as soon as we've read all options */
    if (PostAuthDelay > 0)
        pg_usleep(PostAuthDelay * 1000000L);

    /*
     * Initialize various default states that can't be set up until we've
     * selected the active user and gotten the right GUC settings.
     */

    /* set default namespace search path */
    InitializeSearchPath();

    /* initialize client encoding */
    InitializeClientEncoding();

    /* Initialize this backend's session state. */
    InitializeSession();

    /* report this backend in the PgBackendStatus array */
    if (!bootstrap)
        pgstat_bestart();

    /* close the transaction we started above */
    if (!bootstrap)
        CommitTransactionCommand();
}

/*
 * Process any command-line switches and any additional GUC variable
 * settings passed in the startup packet.
 */
static void
process_startup_options(Port *port, bool am_superuser)
{
    GucContext  gucctx;
    ListCell   *gucopts;

    gucctx = am_superuser ? PGC_SU_BACKEND : PGC_BACKEND;

    /*
     * First process any command-line switches that were included in the
     * startup packet, if we are in a regular backend.
     */
    if (port->cmdline_options != NULL)
    {
        /*
         * The maximum possible number of commandline arguments that could
         * come from port->cmdline_options is (strlen + 1) / 2; see
         * pg_split_opts().
         */
        char      **av;
        int         maxac;
        int         ac;

        maxac = 2 + (strlen(port->cmdline_options) + 1) / 2;

        av = (char **) palloc(maxac * sizeof(char *));
        ac = 0;

        av[ac++] = "postgres";

        pg_split_opts(av, &ac, port->cmdline_options);

        av[ac] = NULL;

        Assert(ac < maxac);

        (void) process_postgres_switches(ac, av, gucctx, NULL);
    }

    /*
     * Process any additional GUC variable settings passed in startup packet.
     * These are handled exactly like command-line variables.
     */
    gucopts = list_head(port->guc_options);
    while (gucopts)
    {
        char       *name;
        char       *value;

        name = lfirst(gucopts);
        gucopts = lnext(port->guc_options, gucopts);

        value = lfirst(gucopts);
        gucopts = lnext(port->guc_options, gucopts);

        SetConfigOption(name, value, gucctx, PGC_S_CLIENT);
    }
}

/*
 * Load GUC settings from pg_db_role_setting.
 *
 * We try specific settings for the database/role combination, as well as
 * general for this database and for this user.
 */
static void
process_settings(Oid databaseid, Oid roleid)
{
    Relation    relsetting;
    Snapshot    snapshot;

    if (!IsUnderPostmaster)
        return;

    relsetting = table_open(DbRoleSettingRelationId, AccessShareLock);

    /* read all the settings under the same snapshot for efficiency */
    snapshot = RegisterSnapshot(GetCatalogSnapshot(DbRoleSettingRelationId));

    /* Later settings are ignored if set earlier. */
    ApplySetting(snapshot, databaseid, roleid, relsetting, PGC_S_DATABASE_USER);
    ApplySetting(snapshot, InvalidOid, roleid, relsetting, PGC_S_USER);
    ApplySetting(snapshot, databaseid, InvalidOid, relsetting, PGC_S_DATABASE);
    ApplySetting(snapshot, InvalidOid, InvalidOid, relsetting, PGC_S_GLOBAL);

    UnregisterSnapshot(snapshot);
    table_close(relsetting, AccessShareLock);
}

/*
 * Backend-shutdown callback.  Do cleanup that we want to be sure happens
 * before all the supporting modules begin to nail their doors shut via
 * their own callbacks.
 *
 * User-level cleanup, such as temp-relation removal and UNLISTEN, happens
 * via separate callbacks that execute before this one.  We don't combine the
 * callbacks because we still want this one to happen if the user-level
 * cleanup fails.
 */
static void
ShutdownPostgres(int code, Datum arg)
{
    /* Make sure we've killed any active transaction */
    AbortOutOfAnyTransaction();

    /*
     * User locks are not released by transaction end, so be sure to release
     * them explicitly.
     */
    LockReleaseAll(USER_LOCKMETHOD, true);
}


/*
 * STATEMENT_TIMEOUT handler: trigger a query-cancel interrupt.
 */
static void
StatementTimeoutHandler(void)
{
    int         sig = SIGINT;

    /*
     * During authentication the timeout is used to deal with
     * authentication_timeout - we want to quit in response to such timeouts.
     */
    if (ClientAuthInProgress)
        sig = SIGTERM;

#ifdef HAVE_SETSID
    /* try to signal whole process group */
    kill(-MyProcPid, sig);
#endif
    kill(MyProcPid, sig);
}

/*
 * LOCK_TIMEOUT handler: trigger a query-cancel interrupt.
 */
static void
LockTimeoutHandler(void)
{
#ifdef HAVE_SETSID
    /* try to signal whole process group */
    kill(-MyProcPid, SIGINT);
#endif
    kill(MyProcPid, SIGINT);
}

static void
IdleInTransactionSessionTimeoutHandler(void)
{
    IdleInTransactionSessionTimeoutPending = true;
    InterruptPending = true;
    SetLatch(MyLatch);
}

static void
IdleSessionTimeoutHandler(void)
{
    IdleSessionTimeoutPending = true;
    InterruptPending = true;
    SetLatch(MyLatch);
}

static void
ClientCheckTimeoutHandler(void)
{
    CheckClientConnectionPending = true;
    InterruptPending = true;
    SetLatch(MyLatch);
}

/*
 * Returns true if at least one role is defined in this database cluster.
 */
static bool
ThereIsAtLeastOneRole(void)
{
    Relation    pg_authid_rel;
    TableScanDesc scan;
    bool        result;

    pg_authid_rel = table_open(AuthIdRelationId, AccessShareLock);

    scan = table_beginscan_catalog(pg_authid_rel, 0, NULL);
    result = (heap_getnext(scan, ForwardScanDirection) != NULL);

    table_endscan(scan);
    table_close(pg_authid_rel, AccessShareLock);

    return result;
}