hi,

> "YAMAMOTO Takashi" <y...@mwd.biglobe.ne.jp> writes:
>> 9.2devel (2562dcea811eb642e1c5442e1ede9fe268278157)
> 
>> ERROR:  could not serialize access due to concurrent update
>> STATEMENT:  UPDATE file SET atime = current_timestamp WHERE fileid = $1
>> TRAP: FailedAssertion("!(owner->nsnapshots == 0)", File: "resowner.c", Line:
>> 365)
>> LOG:  server process (PID 16832) was terminated by signal 6: Abort trap
> 
> There isn't terribly much we can do with this report unless you can
> provide a complete test case to reproduce it.
> 
>                       regards, tom lane

after some investigation, i think it is triggered by protocol-level prepare
of ROLLBACK in an aborted transaction.  does the following patch make sense?

YAMAMOTO Takashi

diff --git a/src/backend/utils/cache/plancache.c 
b/src/backend/utils/cache/plancache.c
index 9cccc87..d1da7df 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -520,6 +520,7 @@ RevalidateCachedQuery(CachedPlanSource *plansource)
         * don't have invalidatable plans, so we'd not get here for such a
         * command.
         */
+       Assert(analyze_requires_snapshot(plansource->raw_parse_tree));
        snapshot_set = false;
        if (!ActiveSnapshotSet())
        {
@@ -757,13 +758,11 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
 
        /*
         * If a snapshot is already set (the normal case), we can just use
-        * that for parsing/planning.  But if it isn't, install one.  Note: no
-        * point in checking whether parse analysis requires a snapshot;
-        * utility commands don't have invalidatable plans, so we'd not get
-        * here for such a command.
+        * that for parsing/planning.  But if it isn't, install one.
         */
        snapshot_set = false;
-       if (!ActiveSnapshotSet())
+       if (!ActiveSnapshotSet() &&
+               analyze_requires_snapshot(plansource->raw_parse_tree))
        {
                PushActiveSnapshot(GetTransactionSnapshot());
                snapshot_set = true;

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