tid.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * tid.c
 *    Functions for the built-in type tuple id
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/tid.c
 *
 * NOTES
 *    input routine largely stolen from boxin().
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <math.h>
#include <limits.h>

#include "access/heapam.h"
#include "access/sysattr.h"
#include "access/tableam.h"
#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "common/hashfn.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "parser/parsetree.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/varlena.h"


#define DatumGetItemPointer(X)   ((ItemPointer) DatumGetPointer(X))
#define ItemPointerGetDatum(X)   PointerGetDatum(X)
#define PG_GETARG_ITEMPOINTER(n) DatumGetItemPointer(PG_GETARG_DATUM(n))
#define PG_RETURN_ITEMPOINTER(x) return ItemPointerGetDatum(x)

#define LDELIM          '('
#define RDELIM          ')'
#define DELIM           ','
#define NTIDARGS        2

static ItemPointer currtid_for_view(Relation viewrel, ItemPointer tid);

/* ----------------------------------------------------------------
 *      tidin
 * ----------------------------------------------------------------
 */
Datum
tidin(PG_FUNCTION_ARGS)
{
    char       *str = PG_GETARG_CSTRING(0);
    char       *p,
               *coord[NTIDARGS];
    int         i;
    ItemPointer result;
    BlockNumber blockNumber;
    OffsetNumber offsetNumber;
    char       *badp;
    int         hold_offset;

    for (i = 0, p = str; *p && i < NTIDARGS && *p != RDELIM; p++)
        if (*p == DELIM || (*p == LDELIM && !i))
            coord[i++] = p + 1;

    if (i < NTIDARGS)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s: \"%s\"",
                        "tid", str)));

    errno = 0;
    blockNumber = strtoul(coord[0], &badp, 10);
    if (errno || *badp != DELIM)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s: \"%s\"",
                        "tid", str)));

    hold_offset = strtol(coord[1], &badp, 10);
    if (errno || *badp != RDELIM ||
        hold_offset > USHRT_MAX || hold_offset < 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s: \"%s\"",
                        "tid", str)));

    offsetNumber = hold_offset;

    result = (ItemPointer) palloc(sizeof(ItemPointerData));

    ItemPointerSet(result, blockNumber, offsetNumber);

    PG_RETURN_ITEMPOINTER(result);
}

/* ----------------------------------------------------------------
 *      tidout
 * ----------------------------------------------------------------
 */
Datum
tidout(PG_FUNCTION_ARGS)
{
    ItemPointer itemPtr = PG_GETARG_ITEMPOINTER(0);
    BlockNumber blockNumber;
    OffsetNumber offsetNumber;
    char        buf[32];

    blockNumber = ItemPointerGetBlockNumberNoCheck(itemPtr);
    offsetNumber = ItemPointerGetOffsetNumberNoCheck(itemPtr);

    /* Perhaps someday we should output this as a record. */
    snprintf(buf, sizeof(buf), "(%u,%u)", blockNumber, offsetNumber);

    PG_RETURN_CSTRING(pstrdup(buf));
}

/*
 *      tidrecv         - converts external binary format to tid
 */
Datum
tidrecv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
    ItemPointer result;
    BlockNumber blockNumber;
    OffsetNumber offsetNumber;

    blockNumber = pq_getmsgint(buf, sizeof(blockNumber));
    offsetNumber = pq_getmsgint(buf, sizeof(offsetNumber));

    result = (ItemPointer) palloc(sizeof(ItemPointerData));

    ItemPointerSet(result, blockNumber, offsetNumber);

    PG_RETURN_ITEMPOINTER(result);
}

/*
 *      tidsend         - converts tid to binary format
 */
Datum
tidsend(PG_FUNCTION_ARGS)
{
    ItemPointer itemPtr = PG_GETARG_ITEMPOINTER(0);
    StringInfoData buf;

    pq_begintypsend(&buf);
    pq_sendint32(&buf, ItemPointerGetBlockNumberNoCheck(itemPtr));
    pq_sendint16(&buf, ItemPointerGetOffsetNumberNoCheck(itemPtr));
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}

/*****************************************************************************
 *   PUBLIC ROUTINES                                                         *
 *****************************************************************************/

Datum
tideq(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_BOOL(ItemPointerCompare(arg1, arg2) == 0);
}

Datum
tidne(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_BOOL(ItemPointerCompare(arg1, arg2) != 0);
}

Datum
tidlt(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_BOOL(ItemPointerCompare(arg1, arg2) < 0);
}

Datum
tidle(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_BOOL(ItemPointerCompare(arg1, arg2) <= 0);
}

Datum
tidgt(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_BOOL(ItemPointerCompare(arg1, arg2) > 0);
}

Datum
tidge(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_BOOL(ItemPointerCompare(arg1, arg2) >= 0);
}

Datum
bttidcmp(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_INT32(ItemPointerCompare(arg1, arg2));
}

Datum
tidlarger(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_ITEMPOINTER(ItemPointerCompare(arg1, arg2) >= 0 ? arg1 : arg2);
}

Datum
tidsmaller(PG_FUNCTION_ARGS)
{
    ItemPointer arg1 = PG_GETARG_ITEMPOINTER(0);
    ItemPointer arg2 = PG_GETARG_ITEMPOINTER(1);

    PG_RETURN_ITEMPOINTER(ItemPointerCompare(arg1, arg2) <= 0 ? arg1 : arg2);
}

Datum
hashtid(PG_FUNCTION_ARGS)
{
    ItemPointer key = PG_GETARG_ITEMPOINTER(0);

    /*
     * While you'll probably have a lot of trouble with a compiler that
     * insists on appending pad space to struct ItemPointerData, we can at
     * least make this code work, by not using sizeof(ItemPointerData).
     * Instead rely on knowing the sizes of the component fields.
     */
    return hash_any((unsigned char *) key,
                    sizeof(BlockIdData) + sizeof(OffsetNumber));
}

Datum
hashtidextended(PG_FUNCTION_ARGS)
{
    ItemPointer key = PG_GETARG_ITEMPOINTER(0);
    uint64      seed = PG_GETARG_INT64(1);

    /* As above */
    return hash_any_extended((unsigned char *) key,
                             sizeof(BlockIdData) + sizeof(OffsetNumber),
                             seed);
}


/*
 *  Functions to get latest tid of a specified tuple.
 *
 *  Maybe these implementations should be moved to another place
 */

/*
 * Utility wrapper for current CTID functions.
 *      Returns the latest version of a tuple pointing at "tid" for
 *      relation "rel".
 */
static ItemPointer
currtid_internal(Relation rel, ItemPointer tid)
{
    ItemPointer result;
    AclResult   aclresult;
    Snapshot    snapshot;
    TableScanDesc scan;

    result = (ItemPointer) palloc(sizeof(ItemPointerData));

    aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
                                  ACL_SELECT);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, get_relkind_objtype(rel->rd_rel->relkind),
                       RelationGetRelationName(rel));

    if (rel->rd_rel->relkind == RELKIND_VIEW)
        return currtid_for_view(rel, tid);

    if (!RELKIND_HAS_STORAGE(rel->rd_rel->relkind))
        elog(ERROR, "cannot look at latest visible tid for relation \"%s.%s\"",
             get_namespace_name(RelationGetNamespace(rel)),
             RelationGetRelationName(rel));

    ItemPointerCopy(tid, result);

    snapshot = RegisterSnapshot(GetLatestSnapshot());
    scan = table_beginscan_tid(rel, snapshot);
    table_tuple_get_latest_tid(scan, result);
    table_endscan(scan);
    UnregisterSnapshot(snapshot);

    return result;
}

/*
 *  Handle CTIDs of views.
 *      CTID should be defined in the view and it must
 *      correspond to the CTID of a base relation.
 */
static ItemPointer
currtid_for_view(Relation viewrel, ItemPointer tid)
{
    TupleDesc   att = RelationGetDescr(viewrel);
    RuleLock   *rulelock;
    RewriteRule *rewrite;
    int         i,
                natts = att->natts,
                tididx = -1;

    for (i = 0; i < natts; i++)
    {
        Form_pg_attribute attr = TupleDescAttr(att, i);

        if (strcmp(NameStr(attr->attname), "ctid") == 0)
        {
            if (attr->atttypid != TIDOID)
                elog(ERROR, "ctid isn't of type TID");
            tididx = i;
            break;
        }
    }
    if (tididx < 0)
        elog(ERROR, "currtid cannot handle views with no CTID");
    rulelock = viewrel->rd_rules;
    if (!rulelock)
        elog(ERROR, "the view has no rules");
    for (i = 0; i < rulelock->numLocks; i++)
    {
        rewrite = rulelock->rules[i];
        if (rewrite->event == CMD_SELECT)
        {
            Query      *query;
            TargetEntry *tle;

            if (list_length(rewrite->actions) != 1)
                elog(ERROR, "only one select rule is allowed in views");
            query = (Query *) linitial(rewrite->actions);
            tle = get_tle_by_resno(query->targetList, tididx + 1);
            if (tle && tle->expr && IsA(tle->expr, Var))
            {
                Var        *var = (Var *) tle->expr;
                RangeTblEntry *rte;

                if (!IS_SPECIAL_VARNO(var->varno) &&
                    var->varattno == SelfItemPointerAttributeNumber)
                {
                    rte = rt_fetch(var->varno, query->rtable);
                    if (rte)
                    {
                        ItemPointer result;
                        Relation    rel;

                        rel = table_open(rte->relid, AccessShareLock);
                        result = currtid_internal(rel, tid);
                        table_close(rel, AccessShareLock);
                        return result;
                    }
                }
            }
            break;
        }
    }
    elog(ERROR, "currtid cannot handle this view");
    return NULL;
}

/*
 * currtid_byrelname
 *      Get the latest tuple version of the tuple pointing at a CTID, for a
 *      given relation name.
 */
Datum
currtid_byrelname(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    ItemPointer tid = PG_GETARG_ITEMPOINTER(1);
    ItemPointer result;
    RangeVar   *relrv;
    Relation    rel;

    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = table_openrv(relrv, AccessShareLock);

    /* grab the latest tuple version associated to this CTID */
    result = currtid_internal(rel, tid);

    table_close(rel, AccessShareLock);

    PG_RETURN_ITEMPOINTER(result);
}