mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-07-15 18:51:09 +02:00
2e44770fa3
Per discussion, it's desirable to eliminate all remaining uses of SnapshotNow, because it has unpleasant semantics: race conditions can result in seeing multiple versions of a concurrently updated row, or none at all. By using GetActiveSnapshot() here, callers will see exactly those rows that would have been visible if the invoking query had scanned the table using, for example, a SELECT statement. This is slightly different from the old behavior, because commits that happen concurrently with the scan will not affect the results. In REPEATABLE READ or SERIALIZABLE modes, where transaction snapshots are used, commits that have happened since the start of the transaction will also not affect the results. It is hoped that this minor incompatibility will be thought an improvement, or at least no worse than what we did before.
301 lines
8.1 KiB
C
301 lines
8.1 KiB
C
/*
|
|
* 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/multixact.h"
|
|
#include "access/relscan.h"
|
|
#include "access/xact.h"
|
|
#include "catalog/namespace.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/tqual.h"
|
|
|
|
|
|
PG_MODULE_MAGIC;
|
|
|
|
PG_FUNCTION_INFO_V1(pgrowlocks);
|
|
|
|
extern Datum pgrowlocks(PG_FUNCTION_ARGS);
|
|
|
|
/* ----------
|
|
* pgrowlocks:
|
|
* returns tids of rows being locked
|
|
* ----------
|
|
*/
|
|
|
|
#define NCHARS 32
|
|
|
|
typedef struct
|
|
{
|
|
Relation rel;
|
|
HeapScanDesc scan;
|
|
int ncolumns;
|
|
} MyData;
|
|
|
|
#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)
|
|
{
|
|
FuncCallContext *funcctx;
|
|
HeapScanDesc scan;
|
|
HeapTuple tuple;
|
|
TupleDesc tupdesc;
|
|
AttInMetadata *attinmeta;
|
|
Datum result;
|
|
MyData *mydata;
|
|
Relation rel;
|
|
|
|
if (SRF_IS_FIRSTCALL())
|
|
{
|
|
text *relname;
|
|
RangeVar *relrv;
|
|
MemoryContext oldcontext;
|
|
AclResult aclresult;
|
|
|
|
funcctx = SRF_FIRSTCALL_INIT();
|
|
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
|
|
|
|
/* Build a tuple descriptor for our result type */
|
|
if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
|
|
elog(ERROR, "return type must be a row type");
|
|
|
|
attinmeta = TupleDescGetAttInMetadata(tupdesc);
|
|
funcctx->attinmeta = attinmeta;
|
|
|
|
relname = PG_GETARG_TEXT_P(0);
|
|
relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
|
|
rel = heap_openrv(relrv, AccessShareLock);
|
|
|
|
/* check permissions: must have SELECT on table */
|
|
aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
|
|
ACL_SELECT);
|
|
if (aclresult != ACLCHECK_OK)
|
|
aclcheck_error(aclresult, ACL_KIND_CLASS,
|
|
RelationGetRelationName(rel));
|
|
|
|
scan = heap_beginscan(rel, GetActiveSnapshot(), 0, NULL);
|
|
mydata = palloc(sizeof(*mydata));
|
|
mydata->rel = rel;
|
|
mydata->scan = scan;
|
|
mydata->ncolumns = tupdesc->natts;
|
|
funcctx->user_fctx = mydata;
|
|
|
|
MemoryContextSwitchTo(oldcontext);
|
|
}
|
|
|
|
funcctx = SRF_PERCALL_SETUP();
|
|
attinmeta = funcctx->attinmeta;
|
|
mydata = (MyData *) funcctx->user_fctx;
|
|
scan = mydata->scan;
|
|
|
|
/* scan the relation */
|
|
while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
|
|
{
|
|
HTSU_Result htsu;
|
|
TransactionId xmax;
|
|
uint16 infomask;
|
|
|
|
/* must hold a buffer lock to call HeapTupleSatisfiesUpdate */
|
|
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
|
|
|
|
htsu = HeapTupleSatisfiesUpdate(tuple,
|
|
GetCurrentCommandId(false),
|
|
scan->rs_cbuf);
|
|
xmax = HeapTupleHeaderGetRawXmax(tuple->t_data);
|
|
infomask = tuple->t_data->t_infomask;
|
|
|
|
/*
|
|
* a tuple is locked if HTSU returns BeingUpdated, and if it returns
|
|
* MayBeUpdated but the Xmax is valid and pointing at us.
|
|
*/
|
|
if (htsu == HeapTupleBeingUpdated ||
|
|
(htsu == HeapTupleMayBeUpdated &&
|
|
!(infomask & HEAP_XMAX_INVALID) &&
|
|
!(infomask & HEAP_XMAX_IS_MULTI) &&
|
|
(xmax == GetCurrentTransactionIdIfAny())))
|
|
{
|
|
char **values;
|
|
|
|
values = (char **) palloc(mydata->ncolumns * sizeof(char *));
|
|
|
|
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 = !(infomask & HEAP_LOCK_MASK) &&
|
|
(infomask & HEAP_XMAX_LOCK_ONLY);
|
|
nmembers = GetMultiXactIdMembers(xmax, &members, allow_old);
|
|
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(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
|
|
|
|
/* build a tuple */
|
|
tuple = BuildTupleFromCStrings(attinmeta, values);
|
|
|
|
/* make the tuple into a datum */
|
|
result = HeapTupleGetDatum(tuple);
|
|
|
|
/*
|
|
* no need to pfree what we allocated; it's on a short-lived
|
|
* memory context anyway
|
|
*/
|
|
|
|
SRF_RETURN_NEXT(funcctx, result);
|
|
}
|
|
else
|
|
{
|
|
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
|
|
}
|
|
}
|
|
|
|
heap_endscan(scan);
|
|
heap_close(mydata->rel, AccessShareLock);
|
|
|
|
SRF_RETURN_DONE(funcctx);
|
|
}
|