Hi,
With a help from Bruce, I wrote a small function which returns row
locking information(see attached file if you are interested). Here is
a sample result:
test=# select * from pgrowlocks('t1');
locked_row | lock_type | locker | multi
------------+-----------+--------+-------
(0,1) | Shared | 1 | t
(0,3) | Exclusive | 575 | f
(2 rows)
I think it will be more usefull if actual xids are shown in the case
"locker" is a multixid. It seems GetMultiXactIdMembers() does the
job. Unfortunately that is a static funtcion, however. Is there any
chance GetMultiXactIdMembers() becomes public funtion?
--
Tatsuo Ishii
/*
* $PostgreSQL$
*
* Copyright (c) 2005 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 "funcapi.h"
#include "access/heapam.h"
#include "access/transam.h"
#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "utils/builtins.h"
PG_FUNCTION_INFO_V1(pgrowlocks);
extern Datum pgrowlocks(PG_FUNCTION_ARGS);
/* ----------
* pgrowlocks:
* returns tids of rows being locked
*
* C FUNCTION definition
* pgrowlocks(text) returns set of pgrowlocks_type
* see pgrowlocks.sql for pgrowlocks_type
* ----------
*/
#define DUMMY_TUPLE "public.pgrowlocks_type"
#define NCHARS 32
/*
* define this if makeRangeVarFromNameList() has two arguments. As far
* as I know, this only happens in 8.0.x.
*/
#undef MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS
typedef struct {
HeapScanDesc scan;
int ncolumns;
} MyData;
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;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext =
MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
tupdesc = RelationNameGetTupleDesc(DUMMY_TUPLE);
attinmeta = TupleDescGetAttInMetadata(tupdesc);
funcctx->attinmeta = attinmeta;
relname = PG_GETARG_TEXT_P(0);
#ifdef MAKERANGEVARFROMNAMELIST_HAS_TWO_ARGS
relrv =
makeRangeVarFromNameList(textToQualifiedNameList(relname,
"pgrowlocks"));
#else
relrv =
makeRangeVarFromNameList(textToQualifiedNameList(relname));
#endif
rel = heap_openrv(relrv, AccessShareLock);
scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
mydata = palloc(sizeof(*mydata));
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)
{
/* must hold a buffer lock to call HeapTupleSatisfiesUpdate */
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
if (HeapTupleSatisfiesUpdate(tuple->t_data,
GetCurrentCommandId(), scan->rs_cbuf)
== HeapTupleBeingUpdated)
{
char **values;
int i;
values = (char **) palloc(mydata->ncolumns *
sizeof(char *));
i = 0;
values[i++] = (char *)DirectFunctionCall1(tidout,
PointerGetDatum(&tuple->t_self));
#ifdef HEAP_XMAX_SHARED_LOCK
if (tuple->t_data->t_infomask & HEAP_XMAX_SHARED_LOCK)
values[i++] = pstrdup("Shared");
else
values[i++] = pstrdup("Exclusive");
#else
values[i++] = pstrdup("Exclusive");
#endif
values[i] = palloc(NCHARS*sizeof(char));
snprintf(values[i++], NCHARS, "%d",
HeapTupleHeaderGetXmax(tuple->t_data));
#ifdef HEAP_XMAX_SHARED_LOCK
if (tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI)
values[i++] = pstrdup("true");
else
values[i++] = pstrdup("false");
#else
values[i++] = pstrdup("false");
#endif
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
/* build a tuple */
tuple = BuildTupleFromCStrings(attinmeta, values);
/* make the tuple into a datum */
result = HeapTupleGetDatum(tuple);
/* Clean up */
for (i = 0; i < mydata->ncolumns; i++)
pfree(values[i]);
pfree(values);
SRF_RETURN_NEXT(funcctx, result);
}
else
{
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
}
}
heap_endscan(scan);
heap_close(scan->rs_rd, AccessShareLock);
SRF_RETURN_DONE(funcctx);
}
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
