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Fix longstanding race condition in plancache.c.

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When creating or manipulating a cached plan for a transaction control
command (particularly ROLLBACK), we must not perform any catalog accesses,
since we might be in an aborted transaction.  However, plancache.c busily
saved or examined the search_path for every cached plan.  If we were
unlucky enough to do this at a moment where the path's expansion into
schema OIDs wasn't already cached, we'd do some catalog accesses; and with
some more bad luck such as an ill-timed signal arrival, that could lead to
crashes or Assert failures, as exhibited in bug #8095 from Nachiket Vaidya.
Fortunately, there's no real need to consider the search path for such
commands, so we can just skip the relevant steps when the subject statement
is a TransactionStmt.  This is somewhat related to bug #5269, though the
failure happens during initial cached-plan creation rather than
revalidation.

This bug has been there since the plan cache was invented, so back-patch
to all supported branches.
This commit is contained in:
Tom Lane
2013-04-20 16:59:31 -04:00
parent d189deebd3
commit c13ed70a4f
1 changed files with 24 additions and 6 deletions
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30
src/backend/utils/cache/plancache.c vendored
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@ -61,6 +61,14 @@
#include "utils/syscache.h"
/*
* We must skip "overhead" operations that involve database access when the
* cached plan's subject statement is a transaction control command.
*/
#define IsTransactionStmtPlan(plansource) \
((plansource)->raw_parse_tree && \
IsA((plansource)->raw_parse_tree, TransactionStmt))
static List *cached_plans_list = NIL;
static void StoreCachedPlan(CachedPlanSource *plansource, List *stmt_list,
@ -136,9 +144,13 @@ CreateCachedPlan(Node *raw_parse_tree,
/*
* Fetch current search_path into new context, but do any recalculation
* work required in caller's context.
* work required in caller's context. Skip this for a transaction control
* command, since we won't need it and can't risk catalog access.
*/
search_path = GetOverrideSearchPath(source_context);
if (raw_parse_tree && IsA(raw_parse_tree, TransactionStmt))
search_path = NULL;
else
search_path = GetOverrideSearchPath(source_context);
/*
* Create and fill the CachedPlanSource struct within the new context.
@ -229,9 +241,13 @@ FastCreateCachedPlan(Node *raw_parse_tree,
/*
* Fetch current search_path into given context, but do any recalculation
* work required in caller's context.
* work required in caller's context. Skip this for a transaction control
* command, since we won't need it and can't risk catalog access.
*/
search_path = GetOverrideSearchPath(context);
if (raw_parse_tree && IsA(raw_parse_tree, TransactionStmt))
search_path = NULL;
else
search_path = GetOverrideSearchPath(context);
/*
* Create and fill the CachedPlanSource struct within the given context.
@ -517,7 +533,8 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
*
* (XXX is there anything else we really need to restore?)
*/
PushOverrideSearchPath(plansource->search_path);
if (plansource->search_path)
PushOverrideSearchPath(plansource->search_path);
/*
* If a snapshot is already set (the normal case), we can just use
@ -601,7 +618,8 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
PopActiveSnapshot();
/* Now we can restore current search path */
PopOverrideSearchPath();
if (plansource->search_path)
PopOverrideSearchPath();
/*
* Store the plans into the plancache entry, advancing the generation