Move routines to manipulate WAL into PostgreSQL::Test::Cluster

[pgsql.git] / src / backend / commands / tablespace.c

/*-------------------------------------------------------------------------
 *
 * 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) 1996-2025, 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/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/objectaccess.h"
#include "catalog/pg_tablespace.h"
#include "commands/comment.h"
#include "commands/seclabel.h"
#include "commands/tablespace.h"
#include "common/file_perm.h"
#include "miscadmin.h"
#include "postmaster/bgwriter.h"
#include "storage/fd.h"
#include "storage/standby.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/guc_hooks.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("%s/%u", PG_TBLSPC_DIR, 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("%s/%u/%s", PG_TBLSPC_DIR, 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 = 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);
}