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List:       pgsql-bugs
Subject:    Re: [BUGS] After promote, DB can not UPDATE with SAVEPOINT (could not access status of transaction 1
From:       ダンミンフーン <dangminh-huong () mxm ! nes ! nec ! co ! jp>
Date:       2013-08-23 0:56:30
Message-ID: 00f401ce9f9b$9abc44e0$d034cea0$ () mxm ! nes ! nec ! co ! jp
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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



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