Re: After promote, DB can not UPDATE with SAVEPOINT (could not access status of transaction 1409172)

Hi Andres,

Thank you for your prompt response.

I've confirmed in REL9_1_STABLE and could not reproduce that issue.
Also confirm the source and did not find problem with it.

Regard,

---
Dang Minh Huong
NEC Soft,Ltd.
http://www.necsoft.com/eng/

> -----Original Message-----
> From: Andres Freund [mailto:andres@2ndquadrant.com]
> Sent: Thursday, August 22, 2013 10:31 PM
> To: ダンミンフーン
> Cc: pgsql-bugs@postgresql.org; 'Akio Iwaasa'
> Subject: Re: [BUGS] After promote, DB can not UPDATE with SAVEPOINT (could not access status of transaction
> 1409172)
>
> Hi,
>
> On 2013-08-22 22:17:40 +0900, ダンミンフーン wrote:
> > I've get found out that issue in my project.
> > Update in PRIMARY while pg_basebackup is performing, Can cause the
> > STANDBY could not UPDATE after promote.
> >
> > In Standby Node, when first XID of a page come, pg_subtrans must be
> > extended by ExtendSUBTRANS function.
> >
> > But if that XID created while pg_basebackup (with "-x" option) was
> > performing, it did not extend.
> >
> > Due to that, after basebackup complete, start that DB and do promote
> > complete. It failed in SAVEPOINT UPDATE query like follows.
> >
> > ---
> > postgres=# BEGIN;
> > postgres=# SAVEPOINT testsavepoint;
> > postgres=# UPDATE test_tbl SET name = 'test';
> > ERROR:  could not access status of transaction 1409172
> > DETAIL:  Could not read from file "pg_subtrans/0015" at offset 131072: Success.
> > ---
> >
> > I've also confirm source and realize that,
> >
> > When StartupXLOG call RecordKnownAssignedTransactionIds  (in the "main
> > redo apply loop"), the "standbyState" still was STANDBY_INITIALIZED,
> > so it is returned without goto ExtendSUBTRANS (to check and extend
> > space for pg_subtrans).
> >
> > Therefor, after STANDBY promote, when UPDATE query made by SAVEPOINT
> > is executed, the process as follow is performed and get the above
> > ERROR in SimpleLruReadPage function.
> >
> > AssignTransactionId => SubTransSetParent => SubTransSetParent =>
> > SimpleLruReadPage
> >
> > I think that ExtendSUBTRANS must be called even if "standbyState"
> > in STANDBY_INITIALIZED in order to avoid the case above.
> >
> > I also attach a patch. Could anyone confirm for me.
>
> Nice diagnosis and thanks for the patch!
>
> I think the the issue has already been fixed while investigating a similar issue, could you verify that the
> current git version works for you?
>
> c.f. commit 99ee15b315c187045a95db7b27fd9d866aea93e0
>
> Greetings,
>
> Andres Freund
>
> --
>  Andres Freund                       http://www.2ndQuadrant.com/
>  PostgreSQL Development, 24x7 Support, Training & Services