[pg-rex/syncrep.git] / src / backend / storage / file / fd.c

/*-------------------------------------------------------------------------
 *
 * fd.c
 *        Virtual file descriptor code.
 *
 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/backend/storage/file/fd.c
 *
 * NOTES:
 *
 * This code manages a cache of 'virtual' file descriptors (VFDs).
 * The server opens many file descriptors for a variety of reasons,
 * including base tables, scratch files (e.g., sort and hash spool
 * files), and random calls to C library routines like system(3); it
 * is quite easy to exceed system limits on the number of open files a
 * single process can have.  (This is around 256 on many modern
 * operating systems, but can be as low as 32 on others.)
 *
 * VFDs are managed as an LRU pool, with actual OS file descriptors
 * being opened and closed as needed.  Obviously, if a routine is
 * opened using these interfaces, all subsequent operations must also
 * be through these interfaces (the File type is not a real file
 * descriptor).
 *
 * For this scheme to work, most (if not all) routines throughout the
 * server should use these interfaces instead of calling the C library
 * routines (e.g., open(2) and fopen(3)) themselves.  Otherwise, we
 * may find ourselves short of real file descriptors anyway.
 *
 * This file used to contain a bunch of stuff to support RAID levels 0
 * (jbod), 1 (duplex) and 5 (xor parity).  That stuff is all gone
 * because the parallel query processing code that called it is all
 * gone.  If you really need it you could get it from the original
 * POSTGRES source.
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <sys/file.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#ifdef HAVE_SYS_RESOURCE_H
#include <sys/resource.h>               /* for getrlimit */
#endif

#include "miscadmin.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/pg_tablespace.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "utils/guc.h"
#include "utils/resowner.h"


/*
 * We must leave some file descriptors free for system(), the dynamic loader,
 * and other code that tries to open files without consulting fd.c.  This
 * is the number left free.  (While we can be pretty sure we won't get
 * EMFILE, there's never any guarantee that we won't get ENFILE due to
 * other processes chewing up FDs.      So it's a bad idea to try to open files
 * without consulting fd.c.  Nonetheless we cannot control all code.)
 *
 * Because this is just a fixed setting, we are effectively assuming that
 * no such code will leave FDs open over the long term; otherwise the slop
 * is likely to be insufficient.  Note in particular that we expect that
 * loading a shared library does not result in any permanent increase in
 * the number of open files.  (This appears to be true on most if not
 * all platforms as of Feb 2004.)
 */
#define NUM_RESERVED_FDS                10

/*
 * If we have fewer than this many usable FDs after allowing for the reserved
 * ones, choke.
 */
#define FD_MINFREE                              10


/*
 * A number of platforms allow individual processes to open many more files
 * than they can really support when *many* processes do the same thing.
 * This GUC parameter lets the DBA limit max_safe_fds to something less than
 * what the postmaster's initial probe suggests will work.
 */
int                     max_files_per_process = 1000;

/*
 * Maximum number of file descriptors to open for either VFD entries or
 * AllocateFile/AllocateDir operations.  This is initialized to a conservative
 * value, and remains that way indefinitely in bootstrap or standalone-backend
 * cases.  In normal postmaster operation, the postmaster calls
 * set_max_safe_fds() late in initialization to update the value, and that
 * value is then inherited by forked subprocesses.
 *
 * Note: the value of max_files_per_process is taken into account while
 * setting this variable, and so need not be tested separately.
 */
static int      max_safe_fds = 32;      /* default if not changed */


/* Debugging.... */

#ifdef FDDEBUG
#define DO_DB(A) A
#else
#define DO_DB(A)                                /* A */
#endif

#define VFD_CLOSED (-1)

#define FileIsValid(file) \
        ((file) > 0 && (file) < (int) SizeVfdCache && VfdCache[file].fileName != NULL)

#define FileIsNotOpen(file) (VfdCache[file].fd == VFD_CLOSED)

#define FileUnknownPos ((off_t) -1)

/* these are the assigned bits in fdstate below: */
#define FD_TEMPORARY            (1 << 0)        /* T = delete when closed */
#define FD_XACT_TEMPORARY       (1 << 1)        /* T = delete at eoXact */

/*
 * Flag to tell whether it's worth scanning VfdCache looking for temp files to
 * close
 */
static bool have_xact_temporary_files = false;

typedef struct vfd
{
        int                     fd;                             /* current FD, or VFD_CLOSED if none */
        unsigned short fdstate;         /* bitflags for VFD's state */
        ResourceOwner resowner;         /* owner, for automatic cleanup */
        File            nextFree;               /* link to next free VFD, if in freelist */
        File            lruMoreRecently;        /* doubly linked recency-of-use list */
        File            lruLessRecently;
        off_t           seekPos;                /* current logical file position */
        char       *fileName;           /* name of file, or NULL for unused VFD */
        /* NB: fileName is malloc'd, and must be free'd when closing the VFD */
        int                     fileFlags;              /* open(2) flags for (re)opening the file */
        int                     fileMode;               /* mode to pass to open(2) */
} Vfd;

/*
 * Virtual File Descriptor array pointer and size.      This grows as
 * needed.      'File' values are indexes into this array.
 * Note that VfdCache[0] is not a usable VFD, just a list header.
 */
static Vfd *VfdCache;
static Size SizeVfdCache = 0;

/*
 * Number of file descriptors known to be in use by VFD entries.
 */
static int      nfile = 0;

/*
 * List of stdio FILEs and <dirent.h> DIRs opened with AllocateFile
 * and AllocateDir.
 *
 * Since we don't want to encourage heavy use of AllocateFile or AllocateDir,
 * it seems OK to put a pretty small maximum limit on the number of
 * simultaneously allocated descs.
 */
#define MAX_ALLOCATED_DESCS  32

typedef enum
{
        AllocateDescFile,
        AllocateDescDir
} AllocateDescKind;

typedef struct
{
        AllocateDescKind kind;
        union
        {
                FILE       *file;
                DIR                *dir;
        }                       desc;
        SubTransactionId create_subid;
} AllocateDesc;

static int      numAllocatedDescs = 0;
static AllocateDesc allocatedDescs[MAX_ALLOCATED_DESCS];

/*
 * Number of temporary files opened during the current session;
 * this is used in generation of tempfile names.
 */
static long tempFileCounter = 0;

/*
 * Array of OIDs of temp tablespaces.  When numTempTableSpaces is -1,
 * this has not been set in the current transaction.
 */
static Oid *tempTableSpaces = NULL;
static int      numTempTableSpaces = -1;
static int      nextTempTableSpace = 0;


/*--------------------
 *
 * Private Routines
 *
 * Delete                  - delete a file from the Lru ring
 * LruDelete       - remove a file from the Lru ring and close its FD
 * Insert                  - put a file at the front of the Lru ring
 * LruInsert       - put a file at the front of the Lru ring and open it
 * ReleaseLruFile  - Release an fd by closing the last entry in the Lru ring
 * AllocateVfd     - grab a free (or new) file record (from VfdArray)
 * FreeVfd                 - free a file record
 *
 * The Least Recently Used ring is a doubly linked list that begins and
 * ends on element zero.  Element zero is special -- it doesn't represent
 * a file and its "fd" field always == VFD_CLOSED.      Element zero is just an
 * anchor that shows us the beginning/end of the ring.
 * Only VFD elements that are currently really open (have an FD assigned) are
 * in the Lru ring.  Elements that are "virtually" open can be recognized
 * by having a non-null fileName field.
 *
 * example:
 *
 *         /--less----\                            /---------\
 *         v               \                      v                       \
 *       #0 --more---> LeastRecentlyUsed --more-\ \
 *        ^\                                                                    | |
 *         \\less--> MostRecentlyUsedFile       <---/ |
 *              \more---/                                        \--less--/
 *
 *--------------------
 */
static void Delete(File file);
static void LruDelete(File file);
static void Insert(File file);
static int      LruInsert(File file);
static bool ReleaseLruFile(void);
static File AllocateVfd(void);
static void FreeVfd(File file);

static int      FileAccess(File file);
static File OpenTemporaryFileInTablespace(Oid tblspcOid, bool rejectError);
static void AtProcExit_Files(int code, Datum arg);
static void CleanupTempFiles(bool isProcExit);
static void RemovePgTempFilesInDir(const char *tmpdirname);
static void RemovePgTempRelationFiles(const char *tsdirname);
static void RemovePgTempRelationFilesInDbspace(const char *dbspacedirname);
static bool looks_like_temp_rel_name(const char *name);


/*
 * pg_fsync --- do fsync with or without writethrough
 */
int
pg_fsync(int fd)
{
        /* #if is to skip the sync_method test if there's no need for it */
#if defined(HAVE_FSYNC_WRITETHROUGH) && !defined(FSYNC_WRITETHROUGH_IS_FSYNC)
        if (sync_method == SYNC_METHOD_FSYNC_WRITETHROUGH)
                return pg_fsync_writethrough(fd);
        else
#endif
                return pg_fsync_no_writethrough(fd);
}


/*
 * pg_fsync_no_writethrough --- same as fsync except does nothing if
 *      enableFsync is off
 */
int
pg_fsync_no_writethrough(int fd)
{
        if (enableFsync)
                return fsync(fd);
        else
                return 0;
}

/*
 * pg_fsync_writethrough
 */
int
pg_fsync_writethrough(int fd)
{
        if (enableFsync)
        {
#ifdef WIN32
                return _commit(fd);
#elif defined(F_FULLFSYNC)
                return (fcntl(fd, F_FULLFSYNC, 0) == -1) ? -1 : 0;
#else
                errno = ENOSYS;
                return -1;
#endif
        }
        else
                return 0;
}

/*
 * pg_fdatasync --- same as fdatasync except does nothing if enableFsync is off
 *
 * Not all platforms have fdatasync; treat as fsync if not available.
 */
int
pg_fdatasync(int fd)
{
        if (enableFsync)
        {
#ifdef HAVE_FDATASYNC
                return fdatasync(fd);
#else
                return fsync(fd);
#endif
        }
        else
                return 0;
}

/*
 * pg_flush_data --- advise OS that the data described won't be needed soon
 *
 * Not all platforms have posix_fadvise; treat as noop if not available.
 */
int
pg_flush_data(int fd, off_t offset, off_t amount)
{
#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
        return posix_fadvise(fd, offset, amount, POSIX_FADV_DONTNEED);
#else
        return 0;
#endif
}


/*
 * InitFileAccess --- initialize this module during backend startup
 *
 * This is called during either normal or standalone backend start.
 * It is *not* called in the postmaster.
 */
void
InitFileAccess(void)
{
        Assert(SizeVfdCache == 0);      /* call me only once */

        /* initialize cache header entry */
        VfdCache = (Vfd *) malloc(sizeof(Vfd));
        if (VfdCache == NULL)
                ereport(FATAL,
                                (errcode(ERRCODE_OUT_OF_MEMORY),
                                 errmsg("out of memory")));

        MemSet((char *) &(VfdCache[0]), 0, sizeof(Vfd));
        VfdCache->fd = VFD_CLOSED;

        SizeVfdCache = 1;

        /* register proc-exit hook to ensure temp files are dropped at exit */
        on_proc_exit(AtProcExit_Files, 0);
}

/*
 * count_usable_fds --- count how many FDs the system will let us open,
 *              and estimate how many are already open.
 *
 * We stop counting if usable_fds reaches max_to_probe.  Note: a small
 * value of max_to_probe might result in an underestimate of already_open;
 * we must fill in any "gaps" in the set of used FDs before the calculation
 * of already_open will give the right answer.  In practice, max_to_probe
 * of a couple of dozen should be enough to ensure good results.
 *
 * We assume stdin (FD 0) is available for dup'ing
 */
static void
count_usable_fds(int max_to_probe, int *usable_fds, int *already_open)
{
        int                *fd;
        int                     size;
        int                     used = 0;
        int                     highestfd = 0;
        int                     j;

#ifdef HAVE_GETRLIMIT
        struct rlimit rlim;
        int                     getrlimit_status;
#endif

        size = 1024;
        fd = (int *) palloc(size * sizeof(int));

#ifdef HAVE_GETRLIMIT
#ifdef RLIMIT_NOFILE                    /* most platforms use RLIMIT_NOFILE */
        getrlimit_status = getrlimit(RLIMIT_NOFILE, &rlim);
#else                                                   /* but BSD doesn't ... */
        getrlimit_status = getrlimit(RLIMIT_OFILE, &rlim);
#endif   /* RLIMIT_NOFILE */
        if (getrlimit_status != 0)
                ereport(WARNING, (errmsg("getrlimit failed: %m")));
#endif   /* HAVE_GETRLIMIT */

        /* dup until failure or probe limit reached */
        for (;;)
        {
                int                     thisfd;

#ifdef HAVE_GETRLIMIT

                /*
                 * don't go beyond RLIMIT_NOFILE; causes irritating kernel logs on
                 * some platforms
                 */
                if (getrlimit_status == 0 && highestfd >= rlim.rlim_cur - 1)
                        break;
#endif

                thisfd = dup(0);
                if (thisfd < 0)
                {
                        /* Expect EMFILE or ENFILE, else it's fishy */
                        if (errno != EMFILE && errno != ENFILE)
                                elog(WARNING, "dup(0) failed after %d successes: %m", used);
                        break;
                }

                if (used >= size)
                {
                        size *= 2;
                        fd = (int *) repalloc(fd, size * sizeof(int));
                }
                fd[used++] = thisfd;

                if (highestfd < thisfd)
                        highestfd = thisfd;

                if (used >= max_to_probe)
                        break;
        }

        /* release the files we opened */
        for (j = 0; j < used; j++)
                close(fd[j]);

        pfree(fd);

        /*
         * Return results.      usable_fds is just the number of successful dups. We
         * assume that the system limit is highestfd+1 (remember 0 is a legal FD
         * number) and so already_open is highestfd+1 - usable_fds.
         */
        *usable_fds = used;
        *already_open = highestfd + 1 - used;
}

/*
 * set_max_safe_fds
 *              Determine number of filedescriptors that fd.c is allowed to use
 */
void
set_max_safe_fds(void)
{
        int                     usable_fds;
        int                     already_open;

        /*----------
         * We want to set max_safe_fds to
         *                      MIN(usable_fds, max_files_per_process - already_open)
         * less the slop factor for files that are opened without consulting
         * fd.c.  This ensures that we won't exceed either max_files_per_process
         * or the experimentally-determined EMFILE limit.
         *----------
         */
        count_usable_fds(max_files_per_process,
                                         &usable_fds, &already_open);

        max_safe_fds = Min(usable_fds, max_files_per_process - already_open);

        /*
         * Take off the FDs reserved for system() etc.
         */
        max_safe_fds -= NUM_RESERVED_FDS;

        /*
         * Make sure we still have enough to get by.
         */
        if (max_safe_fds < FD_MINFREE)
                ereport(FATAL,
                                (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                                 errmsg("insufficient file descriptors available to start server process"),
                                 errdetail("System allows %d, we need at least %d.",
                                                   max_safe_fds + NUM_RESERVED_FDS,
                                                   FD_MINFREE + NUM_RESERVED_FDS)));

        elog(DEBUG2, "max_safe_fds = %d, usable_fds = %d, already_open = %d",
                 max_safe_fds, usable_fds, already_open);
}

/*
 * BasicOpenFile --- same as open(2) except can free other FDs if needed
 *
 * This is exported for use by places that really want a plain kernel FD,
 * but need to be proof against running out of FDs.  Once an FD has been
 * successfully returned, it is the caller's responsibility to ensure that
 * it will not be leaked on ereport()!  Most users should *not* call this
 * routine directly, but instead use the VFD abstraction level, which
 * provides protection against descriptor leaks as well as management of
 * files that need to be open for more than a short period of time.
 *
 * Ideally this should be the *only* direct call of open() in the backend.
 * In practice, the postmaster calls open() directly, and there are some
 * direct open() calls done early in backend startup.  Those are OK since
 * this module wouldn't have any open files to close at that point anyway.
 */
int
BasicOpenFile(FileName fileName, int fileFlags, int fileMode)
{
        int                     fd;

tryAgain:
        fd = open(fileName, fileFlags, fileMode);

        if (fd >= 0)
                return fd;                              /* success! */

        if (errno == EMFILE || errno == ENFILE)
        {
                int                     save_errno = errno;

                ereport(LOG,
                                (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                                 errmsg("out of file descriptors: %m; release and retry")));
                errno = 0;
                if (ReleaseLruFile())
                        goto tryAgain;
                errno = save_errno;
        }

        return -1;                                      /* failure */
}

#if defined(FDDEBUG)

static void
_dump_lru(void)
{
        int                     mru = VfdCache[0].lruLessRecently;
        Vfd                *vfdP = &VfdCache[mru];
        char            buf[2048];

        snprintf(buf, sizeof(buf), "LRU: MOST %d ", mru);
        while (mru != 0)
        {
                mru = vfdP->lruLessRecently;
                vfdP = &VfdCache[mru];
                snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf), "%d ", mru);
        }
        snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf), "LEAST");
        elog(LOG, "%s", buf);
}
#endif   /* FDDEBUG */

static void
Delete(File file)
{
        Vfd                *vfdP;

        Assert(file != 0);

        DO_DB(elog(LOG, "Delete %d (%s)",
                           file, VfdCache[file].fileName));
        DO_DB(_dump_lru());

        vfdP = &VfdCache[file];

        VfdCache[vfdP->lruLessRecently].lruMoreRecently = vfdP->lruMoreRecently;
        VfdCache[vfdP->lruMoreRecently].lruLessRecently = vfdP->lruLessRecently;

        DO_DB(_dump_lru());
}

static void
LruDelete(File file)
{
        Vfd                *vfdP;

        Assert(file != 0);

        DO_DB(elog(LOG, "LruDelete %d (%s)",
                           file, VfdCache[file].fileName));

        vfdP = &VfdCache[file];

        /* delete the vfd record from the LRU ring */
        Delete(file);

        /* save the seek position */
        vfdP->seekPos = lseek(vfdP->fd, (off_t) 0, SEEK_CUR);
        Assert(vfdP->seekPos != (off_t) -1);

        /* close the file */
        if (close(vfdP->fd))
                elog(ERROR, "could not close file \"%s\": %m", vfdP->fileName);

        --nfile;
        vfdP->fd = VFD_CLOSED;
}

static void
Insert(File file)
{
        Vfd                *vfdP;

        Assert(file != 0);

        DO_DB(elog(LOG, "Insert %d (%s)",
                           file, VfdCache[file].fileName));
        DO_DB(_dump_lru());

        vfdP = &VfdCache[file];

        vfdP->lruMoreRecently = 0;
        vfdP->lruLessRecently = VfdCache[0].lruLessRecently;
        VfdCache[0].lruLessRecently = file;
        VfdCache[vfdP->lruLessRecently].lruMoreRecently = file;

        DO_DB(_dump_lru());
}

/* returns 0 on success, -1 on re-open failure (with errno set) */
static int
LruInsert(File file)
{
        Vfd                *vfdP;

        Assert(file != 0);

        DO_DB(elog(LOG, "LruInsert %d (%s)",
                           file, VfdCache[file].fileName));

        vfdP = &VfdCache[file];

        if (FileIsNotOpen(file))
        {
                while (nfile + numAllocatedDescs >= max_safe_fds)
                {
                        if (!ReleaseLruFile())
                                break;
                }

                /*
                 * The open could still fail for lack of file descriptors, eg due to
                 * overall system file table being full.  So, be prepared to release
                 * another FD if necessary...
                 */
                vfdP->fd = BasicOpenFile(vfdP->fileName, vfdP->fileFlags,
                                                                 vfdP->fileMode);
                if (vfdP->fd < 0)
                {
                        DO_DB(elog(LOG, "RE_OPEN FAILED: %d", errno));
                        return vfdP->fd;
                }
                else
                {
                        DO_DB(elog(LOG, "RE_OPEN SUCCESS"));
                        ++nfile;
                }

                /* seek to the right position */
                if (vfdP->seekPos != (off_t) 0)
                {
                        off_t           returnValue;

                        returnValue = lseek(vfdP->fd, vfdP->seekPos, SEEK_SET);
                        Assert(returnValue != (off_t) -1);
                }
        }

        /*
         * put it at the head of the Lru ring
         */

        Insert(file);

        return 0;
}

static bool
ReleaseLruFile(void)
{
        DO_DB(elog(LOG, "ReleaseLruFile. Opened %d", nfile));

        if (nfile > 0)
        {
                /*
                 * There are opened files and so there should be at least one used vfd
                 * in the ring.
                 */
                Assert(VfdCache[0].lruMoreRecently != 0);
                LruDelete(VfdCache[0].lruMoreRecently);
                return true;                    /* freed a file */
        }
        return false;                           /* no files available to free */
}

static File
AllocateVfd(void)
{
        Index           i;
        File            file;

        DO_DB(elog(LOG, "AllocateVfd. Size %lu", SizeVfdCache));

        Assert(SizeVfdCache > 0);       /* InitFileAccess not called? */

        if (VfdCache[0].nextFree == 0)
        {
                /*
                 * The free list is empty so it is time to increase the size of the
                 * array.  We choose to double it each time this happens. However,
                 * there's not much point in starting *real* small.
                 */
                Size            newCacheSize = SizeVfdCache * 2;
                Vfd                *newVfdCache;

                if (newCacheSize < 32)
                        newCacheSize = 32;

                /*
                 * Be careful not to clobber VfdCache ptr if realloc fails.
                 */
                newVfdCache = (Vfd *) realloc(VfdCache, sizeof(Vfd) * newCacheSize);
                if (newVfdCache == NULL)
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory")));
                VfdCache = newVfdCache;

                /*
                 * Initialize the new entries and link them into the free list.
                 */
                for (i = SizeVfdCache; i < newCacheSize; i++)
                {
                        MemSet((char *) &(VfdCache[i]), 0, sizeof(Vfd));
                        VfdCache[i].nextFree = i + 1;
                        VfdCache[i].fd = VFD_CLOSED;
                }
                VfdCache[newCacheSize - 1].nextFree = 0;
                VfdCache[0].nextFree = SizeVfdCache;

                /*
                 * Record the new size
                 */
                SizeVfdCache = newCacheSize;
        }

        file = VfdCache[0].nextFree;

        VfdCache[0].nextFree = VfdCache[file].nextFree;

        return file;
}

static void
FreeVfd(File file)
{
        Vfd                *vfdP = &VfdCache[file];

        DO_DB(elog(LOG, "FreeVfd: %d (%s)",
                           file, vfdP->fileName ? vfdP->fileName : ""));

        if (vfdP->fileName != NULL)
        {
                free(vfdP->fileName);
                vfdP->fileName = NULL;
        }
        vfdP->fdstate = 0x0;

        vfdP->nextFree = VfdCache[0].nextFree;
        VfdCache[0].nextFree = file;
}

/* returns 0 on success, -1 on re-open failure (with errno set) */
static int
FileAccess(File file)
{
        int                     returnValue;

        DO_DB(elog(LOG, "FileAccess %d (%s)",
                           file, VfdCache[file].fileName));

        /*
         * Is the file open?  If not, open it and put it at the head of the LRU
         * ring (possibly closing the least recently used file to get an FD).
         */

        if (FileIsNotOpen(file))
        {
                returnValue = LruInsert(file);
                if (returnValue != 0)
                        return returnValue;
        }
        else if (VfdCache[0].lruLessRecently != file)
        {
                /*
                 * We now know that the file is open and that it is not the last one
                 * accessed, so we need to move it to the head of the Lru ring.
                 */

                Delete(file);
                Insert(file);
        }

        return 0;
}

/*
 *      Called when we get a shared invalidation message on some relation.
 */
#ifdef NOT_USED
void
FileInvalidate(File file)
{
        Assert(FileIsValid(file));
        if (!FileIsNotOpen(file))
                LruDelete(file);
}
#endif

/*
 * open a file in an arbitrary directory
 *
 * NB: if the passed pathname is relative (which it usually is),
 * it will be interpreted relative to the process' working directory
 * (which should always be $PGDATA when this code is running).
 */
File
PathNameOpenFile(FileName fileName, int fileFlags, int fileMode)
{
        char       *fnamecopy;
        File            file;
        Vfd                *vfdP;

        DO_DB(elog(LOG, "PathNameOpenFile: %s %x %o",
                           fileName, fileFlags, fileMode));

        /*
         * We need a malloc'd copy of the file name; fail cleanly if no room.
         */
        fnamecopy = strdup(fileName);
        if (fnamecopy == NULL)
                ereport(ERROR,
                                (errcode(ERRCODE_OUT_OF_MEMORY),
                                 errmsg("out of memory")));

        file = AllocateVfd();
        vfdP = &VfdCache[file];

        while (nfile + numAllocatedDescs >= max_safe_fds)
        {
                if (!ReleaseLruFile())
                        break;
        }

        vfdP->fd = BasicOpenFile(fileName, fileFlags, fileMode);

        if (vfdP->fd < 0)
        {
                FreeVfd(file);
                free(fnamecopy);
                return -1;
        }
        ++nfile;
        DO_DB(elog(LOG, "PathNameOpenFile: success %d",
                           vfdP->fd));

        Insert(file);

        vfdP->fileName = fnamecopy;
        /* Saved flags are adjusted to be OK for re-opening file */
        vfdP->fileFlags = fileFlags & ~(O_CREAT | O_TRUNC | O_EXCL);
        vfdP->fileMode = fileMode;
        vfdP->seekPos = 0;
        vfdP->fdstate = 0x0;
        vfdP->resowner = NULL;

        return file;
}

/*
 * Open a temporary file that will disappear when we close it.
 *
 * This routine takes care of generating an appropriate tempfile name.
 * There's no need to pass in fileFlags or fileMode either, since only
 * one setting makes any sense for a temp file.
 *
 * Unless interXact is true, the file is remembered by CurrentResourceOwner
 * to ensure it's closed and deleted when it's no longer needed, typically at
 * the end-of-transaction. In most cases, you don't want temporary files to
 * outlive the transaction that created them, so this should be false -- but
 * if you need "somewhat" temporary storage, this might be useful. In either
 * case, the file is removed when the File is explicitly closed.
 */
File
OpenTemporaryFile(bool interXact)
{
        File            file = 0;

        /*
         * If some temp tablespace(s) have been given to us, try to use the next
         * one.  If a given tablespace can't be found, we silently fall back to
         * the database's default tablespace.
         *
         * BUT: if the temp file is slated to outlive the current transaction,
         * force it into the database's default tablespace, so that it will not
         * pose a threat to possible tablespace drop attempts.
         */
        if (numTempTableSpaces > 0 && !interXact)
        {
                Oid                     tblspcOid = GetNextTempTableSpace();

                if (OidIsValid(tblspcOid))
                        file = OpenTemporaryFileInTablespace(tblspcOid, false);
        }

        /*
         * If not, or if tablespace is bad, create in database's default
         * tablespace.  MyDatabaseTableSpace should normally be set before we get
         * here, but just in case it isn't, fall back to pg_default tablespace.
         */
        if (file <= 0)
                file = OpenTemporaryFileInTablespace(MyDatabaseTableSpace ?
                                                                                         MyDatabaseTableSpace :
                                                                                         DEFAULTTABLESPACE_OID,
                                                                                         true);

        /* Mark it for deletion at close */
        VfdCache[file].fdstate |= FD_TEMPORARY;

        /* Register it with the current resource owner */
        if (!interXact)
        {
                VfdCache[file].fdstate |= FD_XACT_TEMPORARY;

                ResourceOwnerEnlargeFiles(CurrentResourceOwner);
                ResourceOwnerRememberFile(CurrentResourceOwner, file);
                VfdCache[file].resowner = CurrentResourceOwner;

                /* ensure cleanup happens at eoxact */
                have_xact_temporary_files = true;
        }

        return file;
}

/*
 * Open a temporary file in a specific tablespace.
 * Subroutine for OpenTemporaryFile, which see for details.
 */
static File
OpenTemporaryFileInTablespace(Oid tblspcOid, bool rejectError)
{
        char            tempdirpath[MAXPGPATH];
        char            tempfilepath[MAXPGPATH];
        File            file;

        /*
         * Identify the tempfile directory for this tablespace.
         *
         * If someone tries to specify pg_global, use pg_default instead.
         */
        if (tblspcOid == DEFAULTTABLESPACE_OID ||
                tblspcOid == GLOBALTABLESPACE_OID)
        {
                /* The default tablespace is {datadir}/base */
                snprintf(tempdirpath, sizeof(tempdirpath), "base/%s",
                                 PG_TEMP_FILES_DIR);
        }
        else
        {
                /* All other tablespaces are accessed via symlinks */
                snprintf(tempdirpath, sizeof(tempdirpath), "pg_tblspc/%u/%s/%s",
                                 tblspcOid, TABLESPACE_VERSION_DIRECTORY, PG_TEMP_FILES_DIR);
        }

        /*
         * Generate a tempfile name that should be unique within the current
         * database instance.
         */
        snprintf(tempfilepath, sizeof(tempfilepath), "%s/%s%d.%ld",
                         tempdirpath, PG_TEMP_FILE_PREFIX, MyProcPid, tempFileCounter++);

        /*
         * Open the file.  Note: we don't use O_EXCL, in case there is an orphaned
         * temp file that can be reused.
         */
        file = PathNameOpenFile(tempfilepath,
                                                        O_RDWR | O_CREAT | O_TRUNC | PG_BINARY,
                                                        0600);
        if (file <= 0)
        {
                /*
                 * We might need to create the tablespace's tempfile directory, if no
                 * one has yet done so.
                 *
                 * Don't check for error from mkdir; it could fail if someone else
                 * just did the same thing.  If it doesn't work then we'll bomb out on
                 * the second create attempt, instead.
                 */
                mkdir(tempdirpath, S_IRWXU);

                file = PathNameOpenFile(tempfilepath,
                                                                O_RDWR | O_CREAT | O_TRUNC | PG_BINARY,
                                                                0600);
                if (file <= 0 && rejectError)
                        elog(ERROR, "could not create temporary file \"%s\": %m",
                                 tempfilepath);
        }

        return file;
}

/*
 * close a file when done with it
 */
void
FileClose(File file)
{
        Vfd                *vfdP;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FileClose: %d (%s)",
                           file, VfdCache[file].fileName));

        vfdP = &VfdCache[file];

        if (!FileIsNotOpen(file))
        {
                /* remove the file from the lru ring */
                Delete(file);

                /* close the file */
                if (close(vfdP->fd))
                        elog(ERROR, "could not close file \"%s\": %m", vfdP->fileName);

                --nfile;
                vfdP->fd = VFD_CLOSED;
        }

        /*
         * Delete the file if it was temporary, and make a log entry if wanted
         */
        if (vfdP->fdstate & FD_TEMPORARY)
        {
                /*
                 * If we get an error, as could happen within the ereport/elog calls,
                 * we'll come right back here during transaction abort.  Reset the
                 * flag to ensure that we can't get into an infinite loop.  This code
                 * is arranged to ensure that the worst-case consequence is failing to
                 * emit log message(s), not failing to attempt the unlink.
                 */
                vfdP->fdstate &= ~FD_TEMPORARY;

                if (log_temp_files >= 0)
                {
                        struct stat filestats;
                        int                     stat_errno;

                        /* first try the stat() */
                        if (stat(vfdP->fileName, &filestats))
                                stat_errno = errno;
                        else
                                stat_errno = 0;

                        /* in any case do the unlink */
                        if (unlink(vfdP->fileName))
                                elog(LOG, "could not unlink file \"%s\": %m", vfdP->fileName);

                        /* and last report the stat results */
                        if (stat_errno == 0)
                        {
                                if ((filestats.st_size / 1024) >= log_temp_files)
                                        ereport(LOG,
                                                        (errmsg("temporary file: path \"%s\", size %lu",
                                                                        vfdP->fileName,
                                                                        (unsigned long) filestats.st_size)));
                        }
                        else
                        {
                                errno = stat_errno;
                                elog(LOG, "could not stat file \"%s\": %m", vfdP->fileName);
                        }
                }
                else
                {
                        /* easy case, just do the unlink */
                        if (unlink(vfdP->fileName))
                                elog(LOG, "could not unlink file \"%s\": %m", vfdP->fileName);
                }
        }

        /* Unregister it from the resource owner */
        if (vfdP->resowner)
                ResourceOwnerForgetFile(vfdP->resowner, file);

        /*
         * Return the Vfd slot to the free list
         */
        FreeVfd(file);
}

/*
 * FilePrefetch - initiate asynchronous read of a given range of the file.
 * The logical seek position is unaffected.
 *
 * Currently the only implementation of this function is using posix_fadvise
 * which is the simplest standardized interface that accomplishes this.
 * We could add an implementation using libaio in the future; but note that
 * this API is inappropriate for libaio, which wants to have a buffer provided
 * to read into.
 */
int
FilePrefetch(File file, off_t offset, int amount)
{
#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_WILLNEED)
        int                     returnCode;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FilePrefetch: %d (%s) " INT64_FORMAT " %d",
                           file, VfdCache[file].fileName,
                           (int64) offset, amount));

        returnCode = FileAccess(file);
        if (returnCode < 0)
                return returnCode;

        returnCode = posix_fadvise(VfdCache[file].fd, offset, amount,
                                                           POSIX_FADV_WILLNEED);

        return returnCode;
#else
        Assert(FileIsValid(file));
        return 0;
#endif
}

int
FileRead(File file, char *buffer, int amount)
{
        int                     returnCode;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FileRead: %d (%s) " INT64_FORMAT " %d %p",
                           file, VfdCache[file].fileName,
                           (int64) VfdCache[file].seekPos,
                           amount, buffer));

        returnCode = FileAccess(file);
        if (returnCode < 0)
                return returnCode;

retry:
        returnCode = read(VfdCache[file].fd, buffer, amount);

        if (returnCode >= 0)
                VfdCache[file].seekPos += returnCode;
        else
        {
                /*
                 * Windows may run out of kernel buffers and return "Insufficient
                 * system resources" error.  Wait a bit and retry to solve it.
                 *
                 * It is rumored that EINTR is also possible on some Unix filesystems,
                 * in which case immediate retry is indicated.
                 */
#ifdef WIN32
                DWORD           error = GetLastError();

                switch (error)
                {
                        case ERROR_NO_SYSTEM_RESOURCES:
                                pg_usleep(1000L);
                                errno = EINTR;
                                break;
                        default:
                                _dosmaperr(error);
                                break;
                }
#endif
                /* OK to retry if interrupted */
                if (errno == EINTR)
                        goto retry;

                /* Trouble, so assume we don't know the file position anymore */
                VfdCache[file].seekPos = FileUnknownPos;
        }

        return returnCode;
}

int
FileWrite(File file, char *buffer, int amount)
{
        int                     returnCode;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FileWrite: %d (%s) " INT64_FORMAT " %d %p",
                           file, VfdCache[file].fileName,
                           (int64) VfdCache[file].seekPos,
                           amount, buffer));

        returnCode = FileAccess(file);
        if (returnCode < 0)
                return returnCode;

retry:
        errno = 0;
        returnCode = write(VfdCache[file].fd, buffer, amount);

        /* if write didn't set errno, assume problem is no disk space */
        if (returnCode != amount && errno == 0)
                errno = ENOSPC;

        if (returnCode >= 0)
                VfdCache[file].seekPos += returnCode;
        else
        {
                /*
                 * See comments in FileRead()
                 */
#ifdef WIN32
                DWORD           error = GetLastError();

                switch (error)
                {
                        case ERROR_NO_SYSTEM_RESOURCES:
                                pg_usleep(1000L);
                                errno = EINTR;
                                break;
                        default:
                                _dosmaperr(error);
                                break;
                }
#endif
                /* OK to retry if interrupted */
                if (errno == EINTR)
                        goto retry;

                /* Trouble, so assume we don't know the file position anymore */
                VfdCache[file].seekPos = FileUnknownPos;
        }

        return returnCode;
}

int
FileSync(File file)
{
        int                     returnCode;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FileSync: %d (%s)",
                           file, VfdCache[file].fileName));

        returnCode = FileAccess(file);
        if (returnCode < 0)
                return returnCode;

        return pg_fsync(VfdCache[file].fd);
}

off_t
FileSeek(File file, off_t offset, int whence)
{
        int                     returnCode;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FileSeek: %d (%s) " INT64_FORMAT " " INT64_FORMAT " %d",
                           file, VfdCache[file].fileName,
                           (int64) VfdCache[file].seekPos,
                           (int64) offset, whence));

        if (FileIsNotOpen(file))
        {
                switch (whence)
                {
                        case SEEK_SET:
                                if (offset < 0)
                                        elog(ERROR, "invalid seek offset: " INT64_FORMAT,
                                                 (int64) offset);
                                VfdCache[file].seekPos = offset;
                                break;
                        case SEEK_CUR:
                                VfdCache[file].seekPos += offset;
                                break;
                        case SEEK_END:
                                returnCode = FileAccess(file);
                                if (returnCode < 0)
                                        return returnCode;
                                VfdCache[file].seekPos = lseek(VfdCache[file].fd,
                                                                                           offset, whence);
                                break;
                        default:
                                elog(ERROR, "invalid whence: %d", whence);
                                break;
                }
        }
        else
        {
                switch (whence)
                {
                        case SEEK_SET:
                                if (offset < 0)
                                        elog(ERROR, "invalid seek offset: " INT64_FORMAT,
                                                 (int64) offset);
                                if (VfdCache[file].seekPos != offset)
                                        VfdCache[file].seekPos = lseek(VfdCache[file].fd,
                                                                                                   offset, whence);
                                break;
                        case SEEK_CUR:
                                if (offset != 0 || VfdCache[file].seekPos == FileUnknownPos)
                                        VfdCache[file].seekPos = lseek(VfdCache[file].fd,
                                                                                                   offset, whence);
                                break;
                        case SEEK_END:
                                VfdCache[file].seekPos = lseek(VfdCache[file].fd,
                                                                                           offset, whence);
                                break;
                        default:
                                elog(ERROR, "invalid whence: %d", whence);
                                break;
                }
        }
        return VfdCache[file].seekPos;
}

/*
 * XXX not actually used but here for completeness
 */
#ifdef NOT_USED
off_t
FileTell(File file)
{
        Assert(FileIsValid(file));
        DO_DB(elog(LOG, "FileTell %d (%s)",
                           file, VfdCache[file].fileName));
        return VfdCache[file].seekPos;
}
#endif

int
FileTruncate(File file, off_t offset)
{
        int                     returnCode;

        Assert(FileIsValid(file));

        DO_DB(elog(LOG, "FileTruncate %d (%s)",
                           file, VfdCache[file].fileName));

        returnCode = FileAccess(file);
        if (returnCode < 0)
                return returnCode;

        returnCode = ftruncate(VfdCache[file].fd, offset);
        return returnCode;
}

/*
 * Return the pathname associated with an open file.
 *
 * The returned string points to an internal buffer, which is valid until
 * the file is closed.
 */
char *
FilePathName(File file)
{
        Assert(FileIsValid(file));

        return VfdCache[file].fileName;
}


/*
 * Routines that want to use stdio (ie, FILE*) should use AllocateFile
 * rather than plain fopen().  This lets fd.c deal with freeing FDs if
 * necessary to open the file.  When done, call FreeFile rather than fclose.
 *
 * Note that files that will be open for any significant length of time
 * should NOT be handled this way, since they cannot share kernel file
 * descriptors with other files; there is grave risk of running out of FDs
 * if anyone locks down too many FDs.  Most callers of this routine are
 * simply reading a config file that they will read and close immediately.
 *
 * fd.c will automatically close all files opened with AllocateFile at
 * transaction commit or abort; this prevents FD leakage if a routine
 * that calls AllocateFile is terminated prematurely by ereport(ERROR).
 *
 * Ideally this should be the *only* direct call of fopen() in the backend.
 */
FILE *
AllocateFile(const char *name, const char *mode)
{
        FILE       *file;

        DO_DB(elog(LOG, "AllocateFile: Allocated %d (%s)",
                           numAllocatedDescs, name));

        /*
         * The test against MAX_ALLOCATED_DESCS prevents us from overflowing
         * allocatedFiles[]; the test against max_safe_fds prevents AllocateFile
         * from hogging every one of the available FDs, which'd lead to infinite
         * looping.
         */
        if (numAllocatedDescs >= MAX_ALLOCATED_DESCS ||
                numAllocatedDescs >= max_safe_fds - 1)
                elog(ERROR, "exceeded MAX_ALLOCATED_DESCS while trying to open file \"%s\"",
                         name);

TryAgain:
        if ((file = fopen(name, mode)) != NULL)
        {
                AllocateDesc *desc = &allocatedDescs[numAllocatedDescs];

                desc->kind = AllocateDescFile;
                desc->desc.file = file;
                desc->create_subid = GetCurrentSubTransactionId();
                numAllocatedDescs++;
                return desc->desc.file;
        }

        if (errno == EMFILE || errno == ENFILE)
        {
                int                     save_errno = errno;

                ereport(LOG,
                                (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                                 errmsg("out of file descriptors: %m; release and retry")));
                errno = 0;
                if (ReleaseLruFile())
                        goto TryAgain;
                errno = save_errno;
        }

        return NULL;
}

/*
 * Free an AllocateDesc of either type.
 *
 * The argument *must* point into the allocatedDescs[] array.
 */
static int
FreeDesc(AllocateDesc *desc)
{
        int                     result;

        /* Close the underlying object */
        switch (desc->kind)
        {
                case AllocateDescFile:
                        result = fclose(desc->desc.file);
                        break;
                case AllocateDescDir:
                        result = closedir(desc->desc.dir);
                        break;
                default:
                        elog(ERROR, "AllocateDesc kind not recognized");
                        result = 0;                     /* keep compiler quiet */
                        break;
        }

        /* Compact storage in the allocatedDescs array */
        numAllocatedDescs--;
        *desc = allocatedDescs[numAllocatedDescs];

        return result;
}

/*
 * Close a file returned by AllocateFile.
 *
 * Note we do not check fclose's return value --- it is up to the caller
 * to handle close errors.
 */
int
FreeFile(FILE *file)
{
        int                     i;

        DO_DB(elog(LOG, "FreeFile: Allocated %d", numAllocatedDescs));

        /* Remove file from list of allocated files, if it's present */
        for (i = numAllocatedDescs; --i >= 0;)
        {
                AllocateDesc *desc = &allocatedDescs[i];

                if (desc->kind == AllocateDescFile && desc->desc.file == file)
                        return FreeDesc(desc);
        }

        /* Only get here if someone passes us a file not in allocatedDescs */
        elog(WARNING, "file passed to FreeFile was not obtained from AllocateFile");

        return fclose(file);
}


/*
 * Routines that want to use <dirent.h> (ie, DIR*) should use AllocateDir
 * rather than plain opendir().  This lets fd.c deal with freeing FDs if
 * necessary to open the directory, and with closing it after an elog.
 * When done, call FreeDir rather than closedir.
 *
 * Ideally this should be the *only* direct call of opendir() in the backend.
 */
DIR *
AllocateDir(const char *dirname)
{
        DIR                *dir;

        DO_DB(elog(LOG, "AllocateDir: Allocated %d (%s)",
                           numAllocatedDescs, dirname));

        /*
         * The test against MAX_ALLOCATED_DESCS prevents us from overflowing
         * allocatedDescs[]; the test against max_safe_fds prevents AllocateDir
         * from hogging every one of the available FDs, which'd lead to infinite
         * looping.
         */
        if (numAllocatedDescs >= MAX_ALLOCATED_DESCS ||
                numAllocatedDescs >= max_safe_fds - 1)
                elog(ERROR, "exceeded MAX_ALLOCATED_DESCS while trying to open directory \"%s\"",
                         dirname);

TryAgain:
        if ((dir = opendir(dirname)) != NULL)
        {
                AllocateDesc *desc = &allocatedDescs[numAllocatedDescs];

                desc->kind = AllocateDescDir;
                desc->desc.dir = dir;
                desc->create_subid = GetCurrentSubTransactionId();
                numAllocatedDescs++;
                return desc->desc.dir;
        }

        if (errno == EMFILE || errno == ENFILE)
        {
                int                     save_errno = errno;

                ereport(LOG,
                                (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                                 errmsg("out of file descriptors: %m; release and retry")));
                errno = 0;
                if (ReleaseLruFile())
                        goto TryAgain;
                errno = save_errno;
        }

        return NULL;
}

/*
 * Read a directory opened with AllocateDir, ereport'ing any error.
 *
 * This is easier to use than raw readdir() since it takes care of some
 * otherwise rather tedious and error-prone manipulation of errno.      Also,
 * if you are happy with a generic error message for AllocateDir failure,
 * you can just do
 *
 *              dir = AllocateDir(path);
 *              while ((dirent = ReadDir(dir, path)) != NULL)
 *                      process dirent;
 *              FreeDir(dir);
 *
 * since a NULL dir parameter is taken as indicating AllocateDir failed.
 * (Make sure errno hasn't been changed since AllocateDir if you use this
 * shortcut.)
 *
 * The pathname passed to AllocateDir must be passed to this routine too,
 * but it is only used for error reporting.
 */
struct dirent *
ReadDir(DIR *dir, const char *dirname)
{
        struct dirent *dent;

        /* Give a generic message for AllocateDir failure, if caller didn't */
        if (dir == NULL)
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not open directory \"%s\": %m",
                                                dirname)));

        errno = 0;
        if ((dent = readdir(dir)) != NULL)
                return dent;

#ifdef WIN32

        /*
         * This fix is in mingw cvs (runtime/mingwex/dirent.c rev 1.4), but not in
         * released version
         */
        if (GetLastError() == ERROR_NO_MORE_FILES)
                errno = 0;
#endif

        if (errno)
                ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not read directory \"%s\": %m",
                                                dirname)));
        return NULL;
}

/*
 * Close a directory opened with AllocateDir.
 *
 * Note we do not check closedir's return value --- it is up to the caller
 * to handle close errors.
 */
int
FreeDir(DIR *dir)
{
        int                     i;

        DO_DB(elog(LOG, "FreeDir: Allocated %d", numAllocatedDescs));

        /* Remove dir from list of allocated dirs, if it's present */
        for (i = numAllocatedDescs; --i >= 0;)
        {
                AllocateDesc *desc = &allocatedDescs[i];

                if (desc->kind == AllocateDescDir && desc->desc.dir == dir)
                        return FreeDesc(desc);
        }

        /* Only get here if someone passes us a dir not in allocatedDescs */
        elog(WARNING, "dir passed to FreeDir was not obtained from AllocateDir");

        return closedir(dir);
}


/*
 * closeAllVfds
 *
 * Force all VFDs into the physically-closed state, so that the fewest
 * possible number of kernel file descriptors are in use.  There is no
 * change in the logical state of the VFDs.
 */
void
closeAllVfds(void)
{
        Index           i;

        if (SizeVfdCache > 0)
        {
                Assert(FileIsNotOpen(0));               /* Make sure ring not corrupted */
                for (i = 1; i < SizeVfdCache; i++)
                {
                        if (!FileIsNotOpen(i))
                                LruDelete(i);
                }
        }
}


/*
 * SetTempTablespaces
 *
 * Define a list (actually an array) of OIDs of tablespaces to use for
 * temporary files.  This list will be used until end of transaction,
 * unless this function is called again before then.  It is caller's
 * responsibility that the passed-in array has adequate lifespan (typically
 * it'd be allocated in TopTransactionContext).
 */
void
SetTempTablespaces(Oid *tableSpaces, int numSpaces)
{
        Assert(numSpaces >= 0);
        tempTableSpaces = tableSpaces;
        numTempTableSpaces = numSpaces;

        /*
         * Select a random starting point in the list.  This is to minimize
         * conflicts between backends that are most likely sharing the same list
         * of temp tablespaces.  Note that if we create multiple temp files in the
         * same transaction, we'll advance circularly through the list --- this
         * ensures that large temporary sort files are nicely spread across all
         * available tablespaces.
         */
        if (numSpaces > 1)
                nextTempTableSpace = random() % numSpaces;
        else
                nextTempTableSpace = 0;
}

/*
 * TempTablespacesAreSet
 *
 * Returns TRUE if SetTempTablespaces has been called in current transaction.
 * (This is just so that tablespaces.c doesn't need its own per-transaction
 * state.)
 */
bool
TempTablespacesAreSet(void)
{
        return (numTempTableSpaces >= 0);
}

/*
 * GetNextTempTableSpace
 *
 * Select the next temp tablespace to use.      A result of InvalidOid means
 * to use the current database's default tablespace.
 */
Oid
GetNextTempTableSpace(void)
{
        if (numTempTableSpaces > 0)
        {
                /* Advance nextTempTableSpace counter with wraparound */
                if (++nextTempTableSpace >= numTempTableSpaces)
                        nextTempTableSpace = 0;
                return tempTableSpaces[nextTempTableSpace];
        }
        return InvalidOid;
}


/*
 * AtEOSubXact_Files
 *
 * Take care of subtransaction commit/abort.  At abort, we close temp files
 * that the subtransaction may have opened.  At commit, we reassign the
 * files that were opened to the parent subtransaction.
 */
void
AtEOSubXact_Files(bool isCommit, SubTransactionId mySubid,
                                  SubTransactionId parentSubid)
{
        Index           i;

        for (i = 0; i < numAllocatedDescs; i++)
        {
                if (allocatedDescs[i].create_subid == mySubid)
                {
                        if (isCommit)
                                allocatedDescs[i].create_subid = parentSubid;
                        else
                        {
                                /* have to recheck the item after FreeDesc (ugly) */
                                FreeDesc(&allocatedDescs[i--]);
                        }
                }
        }
}

/*
 * AtEOXact_Files
 *
 * This routine is called during transaction commit or abort (it doesn't
 * particularly care which).  All still-open per-transaction temporary file
 * VFDs are closed, which also causes the underlying files to be deleted
 * (although they should've been closed already by the ResourceOwner
 * cleanup). Furthermore, all "allocated" stdio files are closed. We also
 * forget any transaction-local temp tablespace list.
 */
void
AtEOXact_Files(void)
{
        CleanupTempFiles(false);
        tempTableSpaces = NULL;
        numTempTableSpaces = -1;
}

/*
 * AtProcExit_Files
 *
 * on_proc_exit hook to clean up temp files during backend shutdown.
 * Here, we want to clean up *all* temp files including interXact ones.
 */
static void
AtProcExit_Files(int code, Datum arg)
{
        CleanupTempFiles(true);
}

/*
 * Close temporary files and delete their underlying files.
 *
 * isProcExit: if true, this is being called as the backend process is
 * exiting. If that's the case, we should remove all temporary files; if
 * that's not the case, we are being called for transaction commit/abort
 * and should only remove transaction-local temp files.  In either case,
 * also clean up "allocated" stdio files and dirs.
 */
static void
CleanupTempFiles(bool isProcExit)
{
        Index           i;

        /*
         * Careful here: at proc_exit we need extra cleanup, not just
         * xact_temporary files.
         */
        if (isProcExit || have_xact_temporary_files)
        {
                Assert(FileIsNotOpen(0));               /* Make sure ring not corrupted */
                for (i = 1; i < SizeVfdCache; i++)
                {
                        unsigned short fdstate = VfdCache[i].fdstate;

                        if ((fdstate & FD_TEMPORARY) && VfdCache[i].fileName != NULL)
                        {
                                /*
                                 * If we're in the process of exiting a backend process, close
                                 * all temporary files. Otherwise, only close temporary files
                                 * local to the current transaction. They should be closed by
                                 * the ResourceOwner mechanism already, so this is just a
                                 * debugging cross-check.
                                 */
                                if (isProcExit)
                                        FileClose(i);
                                else if (fdstate & FD_XACT_TEMPORARY)
                                {
                                        elog(WARNING,
                                                 "temporary file %s not closed at end-of-transaction",
                                                 VfdCache[i].fileName);
                                        FileClose(i);
                                }
                        }
                }

                have_xact_temporary_files = false;
        }

        /* Clean up "allocated" stdio files and dirs. */
        while (numAllocatedDescs > 0)
                FreeDesc(&allocatedDescs[0]);
}


/*
 * Remove temporary and temporary relation files left over from a prior
 * postmaster session
 *
 * This should be called during postmaster startup.  It will forcibly
 * remove any leftover files created by OpenTemporaryFile and any leftover
 * temporary relation files created by mdcreate.
 *
 * NOTE: we could, but don't, call this during a post-backend-crash restart
 * cycle.  The argument for not doing it is that someone might want to examine
 * the temp files for debugging purposes.  This does however mean that
 * OpenTemporaryFile had better allow for collision with an existing temp
 * file name.
 */
void
RemovePgTempFiles(void)
{
        char            temp_path[MAXPGPATH];
        DIR                *spc_dir;
        struct dirent *spc_de;

        /*
         * First process temp files in pg_default ($PGDATA/base)
         */
        snprintf(temp_path, sizeof(temp_path), "base/%s", PG_TEMP_FILES_DIR);
        RemovePgTempFilesInDir(temp_path);
        RemovePgTempRelationFiles("base");

        /*
         * Cycle through temp directories for all non-default tablespaces.
         */
        spc_dir = AllocateDir("pg_tblspc");

        while ((spc_de = ReadDir(spc_dir, "pg_tblspc")) != NULL)
        {
                if (strcmp(spc_de->d_name, ".") == 0 ||
                        strcmp(spc_de->d_name, "..") == 0)
                        continue;

                snprintf(temp_path, sizeof(temp_path), "pg_tblspc/%s/%s/%s",
                        spc_de->d_name, TABLESPACE_VERSION_DIRECTORY, PG_TEMP_FILES_DIR);
                RemovePgTempFilesInDir(temp_path);

                snprintf(temp_path, sizeof(temp_path), "pg_tblspc/%s/%s",
                                 spc_de->d_name, TABLESPACE_VERSION_DIRECTORY);
                RemovePgTempRelationFiles(temp_path);
        }

        FreeDir(spc_dir);

        /*
         * In EXEC_BACKEND case there is a pgsql_tmp directory at the top level of
         * DataDir as well.
         */
#ifdef EXEC_BACKEND
        RemovePgTempFilesInDir(PG_TEMP_FILES_DIR);
#endif
}

/* Process one pgsql_tmp directory for RemovePgTempFiles */
static void
RemovePgTempFilesInDir(const char *tmpdirname)
{
        DIR                *temp_dir;
        struct dirent *temp_de;
        char            rm_path[MAXPGPATH];

        temp_dir = AllocateDir(tmpdirname);
        if (temp_dir == NULL)
        {
                /* anything except ENOENT is fishy */
                if (errno != ENOENT)
                        elog(LOG,
                                 "could not open temporary-files directory \"%s\": %m",
                                 tmpdirname);
                return;
        }

        while ((temp_de = ReadDir(temp_dir, tmpdirname)) != NULL)
        {
                if (strcmp(temp_de->d_name, ".") == 0 ||
                        strcmp(temp_de->d_name, "..") == 0)
                        continue;

                snprintf(rm_path, sizeof(rm_path), "%s/%s",
                                 tmpdirname, temp_de->d_name);

                if (strncmp(temp_de->d_name,
                                        PG_TEMP_FILE_PREFIX,
                                        strlen(PG_TEMP_FILE_PREFIX)) == 0)
                        unlink(rm_path);        /* note we ignore any error */
                else
                        elog(LOG,
                                 "unexpected file found in temporary-files directory: \"%s\"",
                                 rm_path);
        }

        FreeDir(temp_dir);
}

/* Process one tablespace directory, look for per-DB subdirectories */
static void
RemovePgTempRelationFiles(const char *tsdirname)
{
        DIR                *ts_dir;
        struct dirent *de;
        char            dbspace_path[MAXPGPATH];

        ts_dir = AllocateDir(tsdirname);
        if (ts_dir == NULL)
        {
                /* anything except ENOENT is fishy */
                if (errno != ENOENT)
                        elog(LOG,
                                 "could not open tablespace directory \"%s\": %m",
                                 tsdirname);
                return;
        }

        while ((de = ReadDir(ts_dir, tsdirname)) != NULL)
        {
                int                     i = 0;

                /*
                 * We're only interested in the per-database directories, which have
                 * numeric names.  Note that this code will also (properly) ignore "."
                 * and "..".
                 */
                while (isdigit((unsigned char) de->d_name[i]))
                        ++i;
                if (de->d_name[i] != '\0' || i == 0)
                        continue;

                snprintf(dbspace_path, sizeof(dbspace_path), "%s/%s",
                                 tsdirname, de->d_name);
                RemovePgTempRelationFilesInDbspace(dbspace_path);
        }

        FreeDir(ts_dir);
}

/* Process one per-dbspace directory for RemovePgTempRelationFiles */
static void
RemovePgTempRelationFilesInDbspace(const char *dbspacedirname)
{
        DIR                *dbspace_dir;
        struct dirent *de;
        char            rm_path[MAXPGPATH];

        dbspace_dir = AllocateDir(dbspacedirname);
        if (dbspace_dir == NULL)
        {
                /* we just saw this directory, so it really ought to be there */
                elog(LOG,
                         "could not open dbspace directory \"%s\": %m",
                         dbspacedirname);
                return;
        }

        while ((de = ReadDir(dbspace_dir, dbspacedirname)) != NULL)
        {
                if (!looks_like_temp_rel_name(de->d_name))
                        continue;

                snprintf(rm_path, sizeof(rm_path), "%s/%s",
                                 dbspacedirname, de->d_name);

                unlink(rm_path);                /* note we ignore any error */
        }

        FreeDir(dbspace_dir);
}

/* t<digits>_<digits>, or t<digits>_<digits>_<forkname> */
static bool
looks_like_temp_rel_name(const char *name)
{
        int                     pos;
        int                     savepos;

        /* Must start with "t". */
        if (name[0] != 't')
                return false;

        /* Followed by a non-empty string of digits and then an underscore. */
        for (pos = 1; isdigit((unsigned char) name[pos]); ++pos)
                ;
        if (pos == 1 || name[pos] != '_')
                return false;

        /* Followed by another nonempty string of digits. */
        for (savepos = ++pos; isdigit((unsigned char) name[pos]); ++pos)
                ;
        if (savepos == pos)
                return false;

        /* We might have _forkname or .segment or both. */
        if (name[pos] == '_')
        {
                int                     forkchar = forkname_chars(&name[pos + 1], NULL);

                if (forkchar <= 0)
                        return false;
                pos += forkchar + 1;
        }
        if (name[pos] == '.')
        {
                int                     segchar;

                for (segchar = 1; isdigit((unsigned char) name[pos + segchar]); ++segchar)
                        ;
                if (segchar <= 1)
                        return false;
                pos += segchar;
        }

        /* Now we should be at the end. */
        if (name[pos] != '\0')
                return false;
        return true;
}