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Fix dynahash.c to suppress hash bucket splits while a hash_seq_search() scan

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is in progress on the same hashtable.  This seems the least invasive way to
fix the recently-recognized problem that a split could cause the scan to
visit entries twice or (with much lower probability) miss them entirely.
The only field-reported problem caused by this is the "failed to re-find
shared lock object" PANIC in COMMIT PREPARED reported by Michel Dorochevsky,
which was caused by multiply visited entries.  However, it seems certain
that mdsync() is vulnerable to missing required fsync's due to missed
entries, and I am fearful that RelationCacheInitializePhase2() might be at
risk as well.  Because of that and the generalized hazard presented by this
bug, back-patch all the supported branches.

Along the way, fix pg_prepared_statement() and pg_cursor() to not assume
that the hashtables they are examining will stay static between calls.
This is risky regardless of the newly noted dynahash problem, because
hash_seq_search() has never promised to cope with deletion of table entries
other than the just-returned one.  There may be no bug here because the only
supported way to call these functions is via ExecMakeTableFunctionResult()
which will cycle them to completion before doing anything very interesting,
but it seems best to get rid of the assumption.  This affects 8.2 and HEAD
only, since those functions weren't there earlier.
This commit is contained in:
Tom Lane
2007-04-26 23:24:46 +00:00
parent 8e90c54480
commit a2e923a652
8 changed files with 396 additions and 160 deletions
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155
src/backend/commands/prepare.c
View File

@ -10,7 +10,7 @@
* Copyright (c) 2002-2007, PostgreSQL Global Development Group
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.73 2007/04/16 18:21:07 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.74 2007/04/26 23:24:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -21,7 +21,7 @@
#include "catalog/pg_type.h"
#include "commands/explain.h"
#include "commands/prepare.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "parser/analyze.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
@ -743,92 +743,99 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, ExplainStmt *stmt,
Datum
pg_prepared_statement(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
HASH_SEQ_STATUS *hash_seq;
PreparedStatement *prep_stmt;
ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
TupleDesc tupdesc;
Tuplestorestate *tupstore;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
/* stuff done only on the first call of the function */
if (SRF_IS_FIRSTCALL())
/* 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_FEATURE_NOT_SUPPORTED),
errmsg("materialize mode required, but it is not " \
"allowed in this context")));
/* need to build tuplestore in query context */
per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
oldcontext = MemoryContextSwitchTo(per_query_ctx);
/*
* build tupdesc for result tuples. This must match the definition of
* the pg_prepared_statements view in system_views.sql
*/
tupdesc = CreateTemplateTupleDesc(5, false);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "statement",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepare_time",
TIMESTAMPTZOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 4, "parameter_types",
REGTYPEARRAYOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 5, "from_sql",
BOOLOID, -1, 0);
/*
* We put all the tuples into a tuplestore in one scan of the hashtable.
* This avoids any issue of the hashtable possibly changing between calls.
*/
tupstore = tuplestore_begin_heap(true, false, work_mem);
/* hash table might be uninitialized */
if (prepared_queries)
{
TupleDesc tupdesc;
MemoryContext oldcontext;
HASH_SEQ_STATUS hash_seq;
PreparedStatement *prep_stmt;
/* create a function context for cross-call persistence */
funcctx = SRF_FIRSTCALL_INIT();
/*
* switch to memory context appropriate for multiple function calls
*/
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
/* allocate memory for user context */
if (prepared_queries)
hash_seq_init(&hash_seq, prepared_queries);
while ((prep_stmt = hash_seq_search(&hash_seq)) != NULL)
{
hash_seq = (HASH_SEQ_STATUS *) palloc(sizeof(HASH_SEQ_STATUS));
hash_seq_init(hash_seq, prepared_queries);
funcctx->user_fctx = (void *) hash_seq;
}
else
funcctx->user_fctx = NULL;
HeapTuple tuple;
Datum values[5];
bool nulls[5];
/*
* build tupdesc for result tuples. This must match the definition of
* the pg_prepared_statements view in system_views.sql
*/
tupdesc = CreateTemplateTupleDesc(5, false);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "statement",
TEXTOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepare_time",
TIMESTAMPTZOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 4, "parameter_types",
REGTYPEARRAYOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 5, "from_sql",
BOOLOID, -1, 0);
/* generate junk in short-term context */
MemoryContextSwitchTo(oldcontext);
funcctx->tuple_desc = BlessTupleDesc(tupdesc);
MemoryContextSwitchTo(oldcontext);
}
MemSet(nulls, 0, sizeof(nulls));
/* stuff done on every call of the function */
funcctx = SRF_PERCALL_SETUP();
hash_seq = (HASH_SEQ_STATUS *) funcctx->user_fctx;
/* if the hash table is uninitialized, we're done */
if (hash_seq == NULL)
SRF_RETURN_DONE(funcctx);
prep_stmt = hash_seq_search(hash_seq);
if (prep_stmt)
{
Datum result;
HeapTuple tuple;
Datum values[5];
bool nulls[5];
MemSet(nulls, 0, sizeof(nulls));
values[0] = DirectFunctionCall1(textin,
values[0] = DirectFunctionCall1(textin,
CStringGetDatum(prep_stmt->stmt_name));
if (prep_stmt->plansource->query_string == NULL)
nulls[1] = true;
else
values[1] = DirectFunctionCall1(textin,
if (prep_stmt->plansource->query_string == NULL)
nulls[1] = true;
else
values[1] = DirectFunctionCall1(textin,
CStringGetDatum(prep_stmt->plansource->query_string));
values[2] = TimestampTzGetDatum(prep_stmt->prepare_time);
values[3] = build_regtype_array(prep_stmt->plansource->param_types,
prep_stmt->plansource->num_params);
values[4] = BoolGetDatum(prep_stmt->from_sql);
values[2] = TimestampTzGetDatum(prep_stmt->prepare_time);
values[3] = build_regtype_array(prep_stmt->plansource->param_types,
prep_stmt->plansource->num_params);
values[4] = BoolGetDatum(prep_stmt->from_sql);
tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
result = HeapTupleGetDatum(tuple);
SRF_RETURN_NEXT(funcctx, result);
tuple = heap_form_tuple(tupdesc, values, nulls);
/* switch to appropriate context while storing the tuple */
MemoryContextSwitchTo(per_query_ctx);
tuplestore_puttuple(tupstore, tuple);
}
}
SRF_RETURN_DONE(funcctx);
/* clean up and return the tuplestore */
tuplestore_donestoring(tupstore);
MemoryContextSwitchTo(oldcontext);
rsinfo->returnMode = SFRM_Materialize;
rsinfo->setResult = tupstore;
rsinfo->setDesc = tupdesc;
return (Datum) 0;
}
/*