On Tue, 02 Feb 2021 at 07:12, Jeff Janes <[email protected]> wrote:
> On Mon, Feb 1, 2021 at 6:09 PM Jeff Janes <[email protected]> wrote:
>
>>
>>
>> create or replace function gibberish(int) returns text language SQL as $_$
>> select left(string_agg(md5(random()::text),$$$$),$1) from
>> generate_series(0,$1/32) $_$;
>>
>> create table j1 as select x, md5(random()::text) as t11, gibberish(1500)
>> as t12 from generate_series(1,20e6) f(x);
>>
>
> I should have added, found it on HEAD, verified it also in 12.5.
>
Here's my analysis:
1) In the explain_ExecutorEnd(), it will create a ExplainState on SQL function
memory context, which is a long-lived, cause the memory grow up.
/*
* Switch to context in which the fcache lives. This ensures that our
* tuplestore etc will have sufficient lifetime. The sub-executor is
* responsible for deleting per-tuple information. (XXX in the case of a
* long-lived FmgrInfo, this policy represents more memory leakage, but
* it's not entirely clear where to keep stuff instead.)
*/
oldcontext = MemoryContextSwitchTo(fcache->fcontext);
2) I try to call pfree() to release ExplainState memory, however, it does not
make sence, I do not know why this does not work? So I try to create it in
queryDesc->estate->es_query_cxt memory context like queryDesc->totaltime, and
it works.
Attached fix the memory leakage in auto_explain. Any thoughts?
--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.
>From 2589cf9c78bbd308b6f300277500c920152ee6f2 Mon Sep 17 00:00:00 2001
From: Japin Li <[email protected]>
Date: Tue, 2 Feb 2021 17:27:21 +0800
Subject: [PATCH v1] Fix memory leak in auto_explain
---
contrib/auto_explain/auto_explain.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/contrib/auto_explain/auto_explain.c b/contrib/auto_explain/auto_explain.c
index faa6231d87..033540a3f4 100644
--- a/contrib/auto_explain/auto_explain.c
+++ b/contrib/auto_explain/auto_explain.c
@@ -383,6 +383,7 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
msec = queryDesc->totaltime->total * 1000.0;
if (msec >= auto_explain_log_min_duration)
{
+ MemoryContext oldctx = MemoryContextSwitchTo(queryDesc->estate->es_query_cxt);
ExplainState *es = NewExplainState();
es->analyze = (queryDesc->instrument_options && auto_explain_log_analyze);
@@ -426,6 +427,7 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
errhidestmt(true)));
pfree(es->str->data);
+ MemoryContextSwitchTo(oldctx);
}
}
--
2.30.0
