pgrowlocks.c

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/*
 * contrib/pgrowlocks/pgrowlocks.c
 *
 * Copyright (c) 2005-2006  Tatsuo Ishii
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose, without fee, and without a
 * written agreement is hereby granted, provided that the above
 * copyright notice and this paragraph and the following two
 * paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS
 * IS" BASIS, AND THE AUTHOR HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
 * SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

#include "postgres.h"

#include "access/heapam.h"
#include "access/multixact.h"
#include "access/relscan.h"
#include "access/tableam.h"
#include "access/xact.h"
#include "catalog/namespace.h"
#include "catalog/pg_am_d.h"
#include "catalog/pg_authid.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/procarray.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
#include "utils/varlena.h"

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(pgrowlocks);

/* ----------
 * pgrowlocks:
 * returns tids of rows being locked
 * ----------
 */

#define NCHARS 32

#define     Atnum_tid       0
#define     Atnum_xmax      1
#define     Atnum_ismulti   2
#define     Atnum_xids      3
#define     Atnum_modes     4
#define     Atnum_pids      5

Datum
pgrowlocks(PG_FUNCTION_ARGS)
{
    text       *relname = PG_GETARG_TEXT_PP(0);
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    bool        randomAccess;
    TupleDesc   tupdesc;
    Tuplestorestate *tupstore;
    AttInMetadata *attinmeta;
    Relation    rel;
    RangeVar   *relrv;
    TableScanDesc scan;
    HeapScanDesc hscan;
    HeapTuple   tuple;
    MemoryContext oldcontext;
    AclResult   aclresult;
    char      **values;

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize))
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("materialize mode required, but it is not allowed in this context")));

    /* The tupdesc and tuplestore must be created in ecxt_per_query_memory */
    oldcontext = MemoryContextSwitchTo(rsinfo->econtext->ecxt_per_query_memory);

    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");

    randomAccess = (rsinfo->allowedModes & SFRM_Materialize_Random) != 0;
    tupstore = tuplestore_begin_heap(randomAccess, false, work_mem);
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = tupstore;
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    /* Access the table */
    relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
    rel = relation_openrv(relrv, AccessShareLock);

    if (rel->rd_rel->relam != HEAP_TABLE_AM_OID)
        ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                        errmsg("only heap AM is supported")));

    if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is a partitioned table",
                        RelationGetRelationName(rel)),
                 errdetail("Partitioned tables do not contain rows.")));
    else if (rel->rd_rel->relkind != RELKIND_RELATION)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table",
                        RelationGetRelationName(rel))));

    /*
     * check permissions: must have SELECT on table or be in
     * pg_stat_scan_tables
     */
    aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
                                  ACL_SELECT);
    if (aclresult != ACLCHECK_OK)
        aclresult = is_member_of_role(GetUserId(), ROLE_PG_STAT_SCAN_TABLES) ? ACLCHECK_OK : ACLCHECK_NO_PRIV;

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

    /* Scan the relation */
    scan = table_beginscan(rel, GetActiveSnapshot(), 0, NULL);
    hscan = (HeapScanDesc) scan;

    attinmeta = TupleDescGetAttInMetadata(tupdesc);

    values = (char **) palloc(tupdesc->natts * sizeof(char *));

    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        TM_Result   htsu;
        TransactionId xmax;
        uint16      infomask;

        /* must hold a buffer lock to call HeapTupleSatisfiesUpdate */
        LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);

        htsu = HeapTupleSatisfiesUpdate(tuple,
                                        GetCurrentCommandId(false),
                                        hscan->rs_cbuf);
        xmax = HeapTupleHeaderGetRawXmax(tuple->t_data);
        infomask = tuple->t_data->t_infomask;

        /*
         * A tuple is locked if HTSU returns BeingModified.
         */
        if (htsu == TM_BeingModified)
        {
            values[Atnum_tid] = (char *) DirectFunctionCall1(tidout,
                                                             PointerGetDatum(&tuple->t_self));

            values[Atnum_xmax] = palloc(NCHARS * sizeof(char));
            snprintf(values[Atnum_xmax], NCHARS, "%d", xmax);
            if (infomask & HEAP_XMAX_IS_MULTI)
            {
                MultiXactMember *members;
                int         nmembers;
                bool        first = true;
                bool        allow_old;

                values[Atnum_ismulti] = pstrdup("true");

                allow_old = HEAP_LOCKED_UPGRADED(infomask);
                nmembers = GetMultiXactIdMembers(xmax, &members, allow_old,
                                                 false);
                if (nmembers == -1)
                {
                    values[Atnum_xids] = "{0}";
                    values[Atnum_modes] = "{transient upgrade status}";
                    values[Atnum_pids] = "{0}";
                }
                else
                {
                    int         j;

                    values[Atnum_xids] = palloc(NCHARS * nmembers);
                    values[Atnum_modes] = palloc(NCHARS * nmembers);
                    values[Atnum_pids] = palloc(NCHARS * nmembers);

                    strcpy(values[Atnum_xids], "{");
                    strcpy(values[Atnum_modes], "{");
                    strcpy(values[Atnum_pids], "{");

                    for (j = 0; j < nmembers; j++)
                    {
                        char        buf[NCHARS];

                        if (!first)
                        {
                            strcat(values[Atnum_xids], ",");
                            strcat(values[Atnum_modes], ",");
                            strcat(values[Atnum_pids], ",");
                        }
                        snprintf(buf, NCHARS, "%d", members[j].xid);
                        strcat(values[Atnum_xids], buf);
                        switch (members[j].status)
                        {
                            case MultiXactStatusUpdate:
                                snprintf(buf, NCHARS, "Update");
                                break;
                            case MultiXactStatusNoKeyUpdate:
                                snprintf(buf, NCHARS, "No Key Update");
                                break;
                            case MultiXactStatusForUpdate:
                                snprintf(buf, NCHARS, "For Update");
                                break;
                            case MultiXactStatusForNoKeyUpdate:
                                snprintf(buf, NCHARS, "For No Key Update");
                                break;
                            case MultiXactStatusForShare:
                                snprintf(buf, NCHARS, "Share");
                                break;
                            case MultiXactStatusForKeyShare:
                                snprintf(buf, NCHARS, "Key Share");
                                break;
                        }
                        strcat(values[Atnum_modes], buf);
                        snprintf(buf, NCHARS, "%d",
                                 BackendXidGetPid(members[j].xid));
                        strcat(values[Atnum_pids], buf);

                        first = false;
                    }

                    strcat(values[Atnum_xids], "}");
                    strcat(values[Atnum_modes], "}");
                    strcat(values[Atnum_pids], "}");
                }
            }
            else
            {
                values[Atnum_ismulti] = pstrdup("false");

                values[Atnum_xids] = palloc(NCHARS * sizeof(char));
                snprintf(values[Atnum_xids], NCHARS, "{%d}", xmax);

                values[Atnum_modes] = palloc(NCHARS);
                if (infomask & HEAP_XMAX_LOCK_ONLY)
                {
                    if (HEAP_XMAX_IS_SHR_LOCKED(infomask))
                        snprintf(values[Atnum_modes], NCHARS, "{For Share}");
                    else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask))
                        snprintf(values[Atnum_modes], NCHARS, "{For Key Share}");
                    else if (HEAP_XMAX_IS_EXCL_LOCKED(infomask))
                    {
                        if (tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED)
                            snprintf(values[Atnum_modes], NCHARS, "{For Update}");
                        else
                            snprintf(values[Atnum_modes], NCHARS, "{For No Key Update}");
                    }
                    else
                        /* neither keyshare nor exclusive bit it set */
                        snprintf(values[Atnum_modes], NCHARS,
                                 "{transient upgrade status}");
                }
                else
                {
                    if (tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED)
                        snprintf(values[Atnum_modes], NCHARS, "{Update}");
                    else
                        snprintf(values[Atnum_modes], NCHARS, "{No Key Update}");
                }

                values[Atnum_pids] = palloc(NCHARS * sizeof(char));
                snprintf(values[Atnum_pids], NCHARS, "{%d}",
                         BackendXidGetPid(xmax));
            }

            LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);

            /* build a tuple */
            tuple = BuildTupleFromCStrings(attinmeta, values);
            tuplestore_puttuple(tupstore, tuple);
        }
        else
        {
            LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_UNLOCK);
        }
    }

    table_endscan(scan);
    table_close(rel, AccessShareLock);
    return (Datum) 0;
}