dbsize.c

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/*
 * dbsize.c
 *      Database object size functions, and related inquiries
 *
 * Copyright (c) 2002-2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/dbsize.c
 *
 */
 
#include "postgres.h"
 
#include <sys/stat.h>
 
#include "access/htup_details.h"
#include "access/relation.h"
#include "catalog/namespace.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_database.h"
#include "catalog/pg_tablespace.h"
#include "commands/dbcommands.h"
#include "commands/tablespace.h"
#include "miscadmin.h"
#include "storage/fd.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/numeric.h"
#include "utils/rel.h"
#include "utils/relfilenumbermap.h"
#include "utils/relmapper.h"
#include "utils/syscache.h"
 
/* Divide by two and round away from zero */
#define half_rounded(x)   (((x) + ((x) < 0 ? -1 : 1)) / 2)
 
/* Units used in pg_size_pretty functions.  All units must be powers of 2 */
struct size_pretty_unit
{
    const char *name;           /* bytes, kB, MB, GB etc */
    uint32      limit;          /* upper limit, prior to half rounding after
                                 * converting to this unit. */
    bool        round;          /* do half rounding for this unit */
    uint8       unitbits;       /* (1 << unitbits) bytes to make 1 of this
                                 * unit */
};
 
/* When adding units here also update the docs and the error message in pg_size_bytes */
static const struct size_pretty_unit size_pretty_units[] = {
    {"bytes", 10 * 1024, false, 0},
    {"kB", 20 * 1024 - 1, true, 10},
    {"MB", 20 * 1024 - 1, true, 20},
    {"GB", 20 * 1024 - 1, true, 30},
    {"TB", 20 * 1024 - 1, true, 40},
    {"PB", 20 * 1024 - 1, true, 50},
    {NULL, 0, false, 0}
};
 
/* Additional unit aliases accepted by pg_size_bytes */
struct size_bytes_unit_alias
{
    const char *alias;
    int         unit_index;     /* corresponding size_pretty_units element */
};
 
/* When adding units here also update the docs and the error message in pg_size_bytes */
static const struct size_bytes_unit_alias size_bytes_aliases[] = {
    {"B", 0},
    {NULL}
};
 
/* Return physical size of directory contents, or 0 if dir doesn't exist */
static int64
db_dir_size(const char *path)
{
    int64       dirsize = 0;
    struct dirent *direntry;
    DIR        *dirdesc;
    char        filename[MAXPGPATH * 2];
 
    dirdesc = AllocateDir(path);
 
    if (!dirdesc)
        return 0;
 
    while ((direntry = ReadDir(dirdesc, path)) != NULL)
    {
        struct stat fst;
 
        CHECK_FOR_INTERRUPTS();
 
        if (strcmp(direntry->d_name, ".") == 0 ||
            strcmp(direntry->d_name, "..") == 0)
            continue;
 
        snprintf(filename, sizeof(filename), "%s/%s", path, direntry->d_name);
 
        if (stat(filename, &fst) < 0)
        {
            if (errno == ENOENT)
                continue;
            else
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not stat file \"%s\": %m", filename)));
        }
        dirsize += fst.st_size;
    }
 
    FreeDir(dirdesc);
    return dirsize;
}
 
/*
 * calculate size of database in all tablespaces
 */
static int64
calculate_database_size(Oid dbOid)
{
    int64       totalsize;
    DIR        *dirdesc;
    struct dirent *direntry;
    char        dirpath[MAXPGPATH];
    char        pathname[MAXPGPATH + 21 + sizeof(TABLESPACE_VERSION_DIRECTORY)];
    AclResult   aclresult;
 
    /*
     * User must have connect privilege for target database or have privileges
     * of pg_read_all_stats
     */
    aclresult = object_aclcheck(DatabaseRelationId, dbOid, GetUserId(), ACL_CONNECT);
    if (aclresult != ACLCHECK_OK &&
        !has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
    {
        aclcheck_error(aclresult, OBJECT_DATABASE,
                       get_database_name(dbOid));
    }
 
    /* Shared storage in pg_global is not counted */
 
    /* Include pg_default storage */
    snprintf(pathname, sizeof(pathname), "base/%u", dbOid);
    totalsize = db_dir_size(pathname);
 
    /* Scan the non-default tablespaces */
    snprintf(dirpath, MAXPGPATH, "pg_tblspc");
    dirdesc = AllocateDir(dirpath);
 
    while ((direntry = ReadDir(dirdesc, dirpath)) != NULL)
    {
        CHECK_FOR_INTERRUPTS();
 
        if (strcmp(direntry->d_name, ".") == 0 ||
            strcmp(direntry->d_name, "..") == 0)
            continue;
 
        snprintf(pathname, sizeof(pathname), "pg_tblspc/%s/%s/%u",
                 direntry->d_name, TABLESPACE_VERSION_DIRECTORY, dbOid);
        totalsize += db_dir_size(pathname);
    }
 
    FreeDir(dirdesc);
 
    return totalsize;
}
 
Datum
pg_database_size_oid(PG_FUNCTION_ARGS)
{
    Oid         dbOid = PG_GETARG_OID(0);
    int64       size;
 
    size = calculate_database_size(dbOid);
 
    if (size == 0)
        PG_RETURN_NULL();
 
    PG_RETURN_INT64(size);
}
 
Datum
pg_database_size_name(PG_FUNCTION_ARGS)
{
    Name        dbName = PG_GETARG_NAME(0);
    Oid         dbOid = get_database_oid(NameStr(*dbName), false);
    int64       size;
 
    size = calculate_database_size(dbOid);
 
    if (size == 0)
        PG_RETURN_NULL();
 
    PG_RETURN_INT64(size);
}
 
 
/*
 * Calculate total size of tablespace. Returns -1 if the tablespace directory
 * cannot be found.
 */
static int64
calculate_tablespace_size(Oid tblspcOid)
{
    char        tblspcPath[MAXPGPATH];
    char        pathname[MAXPGPATH * 2];
    int64       totalsize = 0;
    DIR        *dirdesc;
    struct dirent *direntry;
    AclResult   aclresult;
 
    /*
     * User must have privileges of pg_read_all_stats or have CREATE privilege
     * for target tablespace, either explicitly granted or implicitly because
     * it is default for current database.
     */
    if (tblspcOid != MyDatabaseTableSpace &&
        !has_privs_of_role(GetUserId(), ROLE_PG_READ_ALL_STATS))
    {
        aclresult = object_aclcheck(TableSpaceRelationId, tblspcOid, GetUserId(), ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, OBJECT_TABLESPACE,
                           get_tablespace_name(tblspcOid));
    }
 
    if (tblspcOid == DEFAULTTABLESPACE_OID)
        snprintf(tblspcPath, MAXPGPATH, "base");
    else if (tblspcOid == GLOBALTABLESPACE_OID)
        snprintf(tblspcPath, MAXPGPATH, "global");
    else
        snprintf(tblspcPath, MAXPGPATH, "pg_tblspc/%u/%s", tblspcOid,
                 TABLESPACE_VERSION_DIRECTORY);
 
    dirdesc = AllocateDir(tblspcPath);
 
    if (!dirdesc)
        return -1;
 
    while ((direntry = ReadDir(dirdesc, tblspcPath)) != NULL)
    {
        struct stat fst;
 
        CHECK_FOR_INTERRUPTS();
 
        if (strcmp(direntry->d_name, ".") == 0 ||
            strcmp(direntry->d_name, "..") == 0)
            continue;
 
        snprintf(pathname, sizeof(pathname), "%s/%s", tblspcPath, direntry->d_name);
 
        if (stat(pathname, &fst) < 0)
        {
            if (errno == ENOENT)
                continue;
            else
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not stat file \"%s\": %m", pathname)));
        }
 
        if (S_ISDIR(fst.st_mode))
            totalsize += db_dir_size(pathname);
 
        totalsize += fst.st_size;
    }
 
    FreeDir(dirdesc);
 
    return totalsize;
}
 
Datum
pg_tablespace_size_oid(PG_FUNCTION_ARGS)
{
    Oid         tblspcOid = PG_GETARG_OID(0);
    int64       size;
 
    size = calculate_tablespace_size(tblspcOid);
 
    if (size < 0)
        PG_RETURN_NULL();
 
    PG_RETURN_INT64(size);
}
 
Datum
pg_tablespace_size_name(PG_FUNCTION_ARGS)
{
    Name        tblspcName = PG_GETARG_NAME(0);
    Oid         tblspcOid = get_tablespace_oid(NameStr(*tblspcName), false);
    int64       size;
 
    size = calculate_tablespace_size(tblspcOid);
 
    if (size < 0)
        PG_RETURN_NULL();
 
    PG_RETURN_INT64(size);
}
 
 
/*
 * calculate size of (one fork of) a relation
 *
 * Note: we can safely apply this to temp tables of other sessions, so there
 * is no check here or at the call sites for that.
 */
static int64
calculate_relation_size(RelFileLocator *rfn, ProcNumber backend, ForkNumber forknum)
{
    int64       totalsize = 0;
    char       *relationpath;
    char        pathname[MAXPGPATH];
    unsigned int segcount = 0;
 
    relationpath = relpathbackend(*rfn, backend, forknum);
 
    for (segcount = 0;; segcount++)
    {
        struct stat fst;
 
        CHECK_FOR_INTERRUPTS();
 
        if (segcount == 0)
            snprintf(pathname, MAXPGPATH, "%s",
                     relationpath);
        else
            snprintf(pathname, MAXPGPATH, "%s.%u",
                     relationpath, segcount);
 
        if (stat(pathname, &fst) < 0)
        {
            if (errno == ENOENT)
                break;
            else
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not stat file \"%s\": %m", pathname)));
        }
        totalsize += fst.st_size;
    }
 
    return totalsize;
}
 
Datum
pg_relation_size(PG_FUNCTION_ARGS)
{
    Oid         relOid = PG_GETARG_OID(0);
    text       *forkName = PG_GETARG_TEXT_PP(1);
    Relation    rel;
    int64       size;
 
    rel = try_relation_open(relOid, AccessShareLock);
 
    /*
     * Before 9.2, we used to throw an error if the relation didn't exist, but
     * that makes queries like "SELECT pg_relation_size(oid) FROM pg_class"
     * less robust, because while we scan pg_class with an MVCC snapshot,
     * someone else might drop the table. It's better to return NULL for
     * already-dropped tables than throw an error and abort the whole query.
     */
    if (rel == NULL)
        PG_RETURN_NULL();
 
    size = calculate_relation_size(&(rel->rd_locator), rel->rd_backend,
                                   forkname_to_number(text_to_cstring(forkName)));
 
    relation_close(rel, AccessShareLock);
 
    PG_RETURN_INT64(size);
}
 
/*
 * Calculate total on-disk size of a TOAST relation, including its indexes.
 * Must not be applied to non-TOAST relations.
 */
static int64
calculate_toast_table_size(Oid toastrelid)
{
    int64       size = 0;
    Relation    toastRel;
    ForkNumber  forkNum;
    ListCell   *lc;
    List       *indexlist;
 
    toastRel = relation_open(toastrelid, AccessShareLock);
 
    /* toast heap size, including FSM and VM size */
    for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
        size += calculate_relation_size(&(toastRel->rd_locator),
                                        toastRel->rd_backend, forkNum);
 
    /* toast index size, including FSM and VM size */
    indexlist = RelationGetIndexList(toastRel);
 
    /* Size is calculated using all the indexes available */
    foreach(lc, indexlist)
    {
        Relation    toastIdxRel;
 
        toastIdxRel = relation_open(lfirst_oid(lc),
                                    AccessShareLock);
        for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
            size += calculate_relation_size(&(toastIdxRel->rd_locator),
                                            toastIdxRel->rd_backend, forkNum);
 
        relation_close(toastIdxRel, AccessShareLock);
    }
    list_free(indexlist);
    relation_close(toastRel, AccessShareLock);
 
    return size;
}
 
/*
 * Calculate total on-disk size of a given table,
 * including FSM and VM, plus TOAST table if any.
 * Indexes other than the TOAST table's index are not included.
 *
 * Note that this also behaves sanely if applied to an index or toast table;
 * those won't have attached toast tables, but they can have multiple forks.
 */
static int64
calculate_table_size(Relation rel)
{
    int64       size = 0;
    ForkNumber  forkNum;
 
    /*
     * heap size, including FSM and VM
     */
    for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
        size += calculate_relation_size(&(rel->rd_locator), rel->rd_backend,
                                        forkNum);
 
    /*
     * Size of toast relation
     */
    if (OidIsValid(rel->rd_rel->reltoastrelid))
        size += calculate_toast_table_size(rel->rd_rel->reltoastrelid);
 
    return size;
}
 
/*
 * Calculate total on-disk size of all indexes attached to the given table.
 *
 * Can be applied safely to an index, but you'll just get zero.
 */
static int64
calculate_indexes_size(Relation rel)
{
    int64       size = 0;
 
    /*
     * Aggregate all indexes on the given relation
     */
    if (rel->rd_rel->relhasindex)
    {
        List       *index_oids = RelationGetIndexList(rel);
        ListCell   *cell;
 
        foreach(cell, index_oids)
        {
            Oid         idxOid = lfirst_oid(cell);
            Relation    idxRel;
            ForkNumber  forkNum;
 
            idxRel = relation_open(idxOid, AccessShareLock);
 
            for (forkNum = 0; forkNum <= MAX_FORKNUM; forkNum++)
                size += calculate_relation_size(&(idxRel->rd_locator),
                                                idxRel->rd_backend,
                                                forkNum);
 
            relation_close(idxRel, AccessShareLock);
        }
 
        list_free(index_oids);
    }
 
    return size;
}
 
Datum
pg_table_size(PG_FUNCTION_ARGS)
{
    Oid         relOid = PG_GETARG_OID(0);
    Relation    rel;
    int64       size;
 
    rel = try_relation_open(relOid, AccessShareLock);
 
    if (rel == NULL)
        PG_RETURN_NULL();
 
    size = calculate_table_size(rel);
 
    relation_close(rel, AccessShareLock);
 
    PG_RETURN_INT64(size);
}
 
Datum
pg_indexes_size(PG_FUNCTION_ARGS)
{
    Oid         relOid = PG_GETARG_OID(0);
    Relation    rel;
    int64       size;
 
    rel = try_relation_open(relOid, AccessShareLock);
 
    if (rel == NULL)
        PG_RETURN_NULL();
 
    size = calculate_indexes_size(rel);
 
    relation_close(rel, AccessShareLock);
 
    PG_RETURN_INT64(size);
}
 
/*
 *  Compute the on-disk size of all files for the relation,
 *  including heap data, index data, toast data, FSM, VM.
 */
static int64
calculate_total_relation_size(Relation rel)
{
    int64       size;
 
    /*
     * Aggregate the table size, this includes size of the heap, toast and
     * toast index with free space and visibility map
     */
    size = calculate_table_size(rel);
 
    /*
     * Add size of all attached indexes as well
     */
    size += calculate_indexes_size(rel);
 
    return size;
}
 
Datum
pg_total_relation_size(PG_FUNCTION_ARGS)
{
    Oid         relOid = PG_GETARG_OID(0);
    Relation    rel;
    int64       size;
 
    rel = try_relation_open(relOid, AccessShareLock);
 
    if (rel == NULL)
        PG_RETURN_NULL();
 
    size = calculate_total_relation_size(rel);
 
    relation_close(rel, AccessShareLock);
 
    PG_RETURN_INT64(size);
}
 
/*
 * formatting with size units
 */
Datum
pg_size_pretty(PG_FUNCTION_ARGS)
{
    int64       size = PG_GETARG_INT64(0);
    char        buf[64];
    const struct size_pretty_unit *unit;
 
    for (unit = size_pretty_units; unit->name != NULL; unit++)
    {
        uint8       bits;
 
        /* use this unit if there are no more units or we're below the limit */
        if (unit[1].name == NULL || i64abs(size) < unit->limit)
        {
            if (unit->round)
                size = half_rounded(size);
 
            snprintf(buf, sizeof(buf), INT64_FORMAT " %s", size, unit->name);
            break;
        }
 
        /*
         * Determine the number of bits to use to build the divisor.  We may
         * need to use 1 bit less than the difference between this and the
         * next unit if the next unit uses half rounding.  Or we may need to
         * shift an extra bit if this unit uses half rounding and the next one
         * does not.  We use division rather than shifting right by this
         * number of bits to ensure positive and negative values are rounded
         * in the same way.
         */
        bits = (unit[1].unitbits - unit->unitbits - (unit[1].round == true)
                + (unit->round == true));
        size /= ((int64) 1) << bits;
    }
 
    PG_RETURN_TEXT_P(cstring_to_text(buf));
}
 
static char *
numeric_to_cstring(Numeric n)
{
    Datum       d = NumericGetDatum(n);
 
    return DatumGetCString(DirectFunctionCall1(numeric_out, d));
}
 
static bool
numeric_is_less(Numeric a, Numeric b)
{
    Datum       da = NumericGetDatum(a);
    Datum       db = NumericGetDatum(b);
 
    return DatumGetBool(DirectFunctionCall2(numeric_lt, da, db));
}
 
static Numeric
numeric_absolute(Numeric n)
{
    Datum       d = NumericGetDatum(n);
    Datum       result;
 
    result = DirectFunctionCall1(numeric_abs, d);
    return DatumGetNumeric(result);
}
 
static Numeric
numeric_half_rounded(Numeric n)
{
    Datum       d = NumericGetDatum(n);
    Datum       zero;
    Datum       one;
    Datum       two;
    Datum       result;
 
    zero = NumericGetDatum(int64_to_numeric(0));
    one = NumericGetDatum(int64_to_numeric(1));
    two = NumericGetDatum(int64_to_numeric(2));
 
    if (DatumGetBool(DirectFunctionCall2(numeric_ge, d, zero)))
        d = DirectFunctionCall2(numeric_add, d, one);
    else
        d = DirectFunctionCall2(numeric_sub, d, one);
 
    result = DirectFunctionCall2(numeric_div_trunc, d, two);
    return DatumGetNumeric(result);
}
 
static Numeric
numeric_truncated_divide(Numeric n, int64 divisor)
{
    Datum       d = NumericGetDatum(n);
    Datum       divisor_numeric;
    Datum       result;
 
    divisor_numeric = NumericGetDatum(int64_to_numeric(divisor));
    result = DirectFunctionCall2(numeric_div_trunc, d, divisor_numeric);
    return DatumGetNumeric(result);
}
 
Datum
pg_size_pretty_numeric(PG_FUNCTION_ARGS)
{
    Numeric     size = PG_GETARG_NUMERIC(0);
    char       *result = NULL;
    const struct size_pretty_unit *unit;
 
    for (unit = size_pretty_units; unit->name != NULL; unit++)
    {
        unsigned int shiftby;
 
        /* use this unit if there are no more units or we're below the limit */
        if (unit[1].name == NULL ||
            numeric_is_less(numeric_absolute(size),
                            int64_to_numeric(unit->limit)))
        {
            if (unit->round)
                size = numeric_half_rounded(size);
 
            result = psprintf("%s %s", numeric_to_cstring(size), unit->name);
            break;
        }
 
        /*
         * Determine the number of bits to use to build the divisor.  We may
         * need to use 1 bit less than the difference between this and the
         * next unit if the next unit uses half rounding.  Or we may need to
         * shift an extra bit if this unit uses half rounding and the next one
         * does not.
         */
        shiftby = (unit[1].unitbits - unit->unitbits - (unit[1].round == true)
                   + (unit->round == true));
        size = numeric_truncated_divide(size, ((int64) 1) << shiftby);
    }
 
    PG_RETURN_TEXT_P(cstring_to_text(result));
}
 
/*
 * Convert a human-readable size to a size in bytes
 */
Datum
pg_size_bytes(PG_FUNCTION_ARGS)
{
    text       *arg = PG_GETARG_TEXT_PP(0);
    char       *str,
               *strptr,
               *endptr;
    char        saved_char;
    Numeric     num;
    int64       result;
    bool        have_digits = false;
 
    str = text_to_cstring(arg);
 
    /* Skip leading whitespace */
    strptr = str;
    while (isspace((unsigned char) *strptr))
        strptr++;
 
    /* Check that we have a valid number and determine where it ends */
    endptr = strptr;
 
    /* Part (1): sign */
    if (*endptr == '-' || *endptr == '+')
        endptr++;
 
    /* Part (2): main digit string */
    if (isdigit((unsigned char) *endptr))
    {
        have_digits = true;
        do
            endptr++;
        while (isdigit((unsigned char) *endptr));
    }
 
    /* Part (3): optional decimal point and fractional digits */
    if (*endptr == '.')
    {
        endptr++;
        if (isdigit((unsigned char) *endptr))
        {
            have_digits = true;
            do
                endptr++;
            while (isdigit((unsigned char) *endptr));
        }
    }
 
    /* Complain if we don't have a valid number at this point */
    if (!have_digits)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid size: \"%s\"", str)));
 
    /* Part (4): optional exponent */
    if (*endptr == 'e' || *endptr == 'E')
    {
        long        exponent;
        char       *cp;
 
        /*
         * Note we might one day support EB units, so if what follows 'E'
         * isn't a number, just treat it all as a unit to be parsed.
         */
        exponent = strtol(endptr + 1, &cp, 10);
        (void) exponent;        /* Silence -Wunused-result warnings */
        if (cp > endptr + 1)
            endptr = cp;
    }
 
    /*
     * Parse the number, saving the next character, which may be the first
     * character of the unit string.
     */
    saved_char = *endptr;
    *endptr = '\0';
 
    num = DatumGetNumeric(DirectFunctionCall3(numeric_in,
                                              CStringGetDatum(strptr),
                                              ObjectIdGetDatum(InvalidOid),
                                              Int32GetDatum(-1)));
 
    *endptr = saved_char;
 
    /* Skip whitespace between number and unit */
    strptr = endptr;
    while (isspace((unsigned char) *strptr))
        strptr++;
 
    /* Handle possible unit */
    if (*strptr != '\0')
    {
        const struct size_pretty_unit *unit;
        int64       multiplier = 0;
 
        /* Trim any trailing whitespace */
        endptr = str + VARSIZE_ANY_EXHDR(arg) - 1;
 
        while (isspace((unsigned char) *endptr))
            endptr--;
 
        endptr++;
        *endptr = '\0';
 
        for (unit = size_pretty_units; unit->name != NULL; unit++)
        {
            /* Parse the unit case-insensitively */
            if (pg_strcasecmp(strptr, unit->name) == 0)
                break;
        }
 
        /* If not found, look in table of aliases */
        if (unit->name == NULL)
        {
            for (const struct size_bytes_unit_alias *a = size_bytes_aliases; a->alias != NULL; a++)
            {
                if (pg_strcasecmp(strptr, a->alias) == 0)
                {
                    unit = &size_pretty_units[a->unit_index];
                    break;
                }
            }
        }
 
        /* Verify we found a valid unit in the loop above */
        if (unit->name == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("invalid size: \"%s\"", text_to_cstring(arg)),
                     errdetail("Invalid size unit: \"%s\".", strptr),
                     errhint("Valid units are \"bytes\", \"B\", \"kB\", \"MB\", \"GB\", \"TB\", and \"PB\".")));
 
        multiplier = ((int64) 1) << unit->unitbits;
 
        if (multiplier > 1)
        {
            Numeric     mul_num;
 
            mul_num = int64_to_numeric(multiplier);
 
            num = DatumGetNumeric(DirectFunctionCall2(numeric_mul,
                                                      NumericGetDatum(mul_num),
                                                      NumericGetDatum(num)));
        }
    }
 
    result = DatumGetInt64(DirectFunctionCall1(numeric_int8,
                                               NumericGetDatum(num)));
 
    PG_RETURN_INT64(result);
}
 
/*
 * Get the filenode of a relation
 *
 * This is expected to be used in queries like
 *      SELECT pg_relation_filenode(oid) FROM pg_class;
 * That leads to a couple of choices.  We work from the pg_class row alone
 * rather than actually opening each relation, for efficiency.  We don't
 * fail if we can't find the relation --- some rows might be visible in
 * the query's MVCC snapshot even though the relations have been dropped.
 * (Note: we could avoid using the catcache, but there's little point
 * because the relation mapper also works "in the now".)  We also don't
 * fail if the relation doesn't have storage.  In all these cases it
 * seems better to quietly return NULL.
 */
Datum
pg_relation_filenode(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    RelFileNumber result;
    HeapTuple   tuple;
    Form_pg_class relform;
 
    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        PG_RETURN_NULL();
    relform = (Form_pg_class) GETSTRUCT(tuple);
 
    if (RELKIND_HAS_STORAGE(relform->relkind))
    {
        if (relform->relfilenode)
            result = relform->relfilenode;
        else                    /* Consult the relation mapper */
            result = RelationMapOidToFilenumber(relid,
                                                relform->relisshared);
    }
    else
    {
        /* no storage, return NULL */
        result = InvalidRelFileNumber;
    }
 
    ReleaseSysCache(tuple);
 
    if (!RelFileNumberIsValid(result))
        PG_RETURN_NULL();
 
    PG_RETURN_OID(result);
}
 
/*
 * Get the relation via (reltablespace, relfilenumber)
 *
 * This is expected to be used when somebody wants to match an individual file
 * on the filesystem back to its table. That's not trivially possible via
 * pg_class, because that doesn't contain the relfilenumbers of shared and nailed
 * tables.
 *
 * We don't fail but return NULL if we cannot find a mapping.
 *
 * InvalidOid can be passed instead of the current database's default
 * tablespace.
 */
Datum
pg_filenode_relation(PG_FUNCTION_ARGS)
{
    Oid         reltablespace = PG_GETARG_OID(0);
    RelFileNumber relfilenumber = PG_GETARG_OID(1);
    Oid         heaprel;
 
    /* test needed so RelidByRelfilenumber doesn't misbehave */
    if (!RelFileNumberIsValid(relfilenumber))
        PG_RETURN_NULL();
 
    heaprel = RelidByRelfilenumber(reltablespace, relfilenumber);
 
    if (!OidIsValid(heaprel))
        PG_RETURN_NULL();
    else
        PG_RETURN_OID(heaprel);
}
 
/*
 * Get the pathname (relative to $PGDATA) of a relation
 *
 * See comments for pg_relation_filenode.
 */
Datum
pg_relation_filepath(PG_FUNCTION_ARGS)
{
    Oid         relid = PG_GETARG_OID(0);
    HeapTuple   tuple;
    Form_pg_class relform;
    RelFileLocator rlocator;
    ProcNumber  backend;
    char       *path;
 
    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        PG_RETURN_NULL();
    relform = (Form_pg_class) GETSTRUCT(tuple);
 
    if (RELKIND_HAS_STORAGE(relform->relkind))
    {
        /* This logic should match RelationInitPhysicalAddr */
        if (relform->reltablespace)
            rlocator.spcOid = relform->reltablespace;
        else
            rlocator.spcOid = MyDatabaseTableSpace;
        if (rlocator.spcOid == GLOBALTABLESPACE_OID)
            rlocator.dbOid = InvalidOid;
        else
            rlocator.dbOid = MyDatabaseId;
        if (relform->relfilenode)
            rlocator.relNumber = relform->relfilenode;
        else                    /* Consult the relation mapper */
            rlocator.relNumber = RelationMapOidToFilenumber(relid,
                                                            relform->relisshared);
    }
    else
    {
        /* no storage, return NULL */
        rlocator.relNumber = InvalidRelFileNumber;
        /* some compilers generate warnings without these next two lines */
        rlocator.dbOid = InvalidOid;
        rlocator.spcOid = InvalidOid;
    }
 
    if (!RelFileNumberIsValid(rlocator.relNumber))
    {
        ReleaseSysCache(tuple);
        PG_RETURN_NULL();
    }
 
    /* Determine owning backend. */
    switch (relform->relpersistence)
    {
        case RELPERSISTENCE_UNLOGGED:
        case RELPERSISTENCE_PERMANENT:
            backend = INVALID_PROC_NUMBER;
            break;
        case RELPERSISTENCE_TEMP:
            if (isTempOrTempToastNamespace(relform->relnamespace))
                backend = ProcNumberForTempRelations();
            else
            {
                /* Do it the hard way. */
                backend = GetTempNamespaceProcNumber(relform->relnamespace);
                Assert(backend != INVALID_PROC_NUMBER);
            }
            break;
        default:
            elog(ERROR, "invalid relpersistence: %c", relform->relpersistence);
            backend = INVALID_PROC_NUMBER;  /* placate compiler */
            break;
    }
 
    ReleaseSysCache(tuple);
 
    path = relpathbackend(rlocator, backend, MAIN_FORKNUM);
 
    PG_RETURN_TEXT_P(cstring_to_text(path));
}