Date: Thu, 14 Sep 2006 10:22:22 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Gregory Stark <stark@enterprisedb.com>,
	ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>,
	Bruce Momjian <bruce@momjian.us>, pgsql-hackers@postgresql.org
Subject: Re: CSStorm occurred again by postgreSQL8.2
Message-ID: <20060914142222.GA525@alvh.no-ip.org>
Mail-Followup-To: Tom Lane <tgl@sss.pgh.pa.us>,
	Gregory Stark <stark@enterprisedb.com>,
	ITAGAKI Takahiro <itagaki.takahiro@oss.ntt.co.jp>,
	Bruce Momjian <bruce@momjian.us>, pgsql-hackers@postgresql.org
References: <20060808110913.50FA.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
	<200608260346.k7Q3k2g06954@momjian.us>
	<20060828181312.5638.ITAGAKI.TAKAHIRO@oss.ntt.co.jp>
	<13251.1157299738@sss.pgh.pa.us> <22080.1158198335@sss.pgh.pa.us>
	<87mz92so6n.fsf@enterprisedb.com> <27509.1158237711@sss.pgh.pa.us>
	<28167.1158241250@sss.pgh.pa.us> <28515.1158242279@sss.pgh.pa.us>
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Tom Lane wrote:
> I wrote:
> > I see a bug though, which is that RecordSubTransactionAbort() calls
> > GetCurrentTransactionId() before having verified that it needs to do
> > anything.  This means that we'll generate and then discard an XID
> > uselessly in a failed subxact that didn't touch disk.
> 
> Well, it would be a bug except that RecordSubTransactionAbort isn't
> called unless the current subxact has an XID.  Perhaps a comment would
> be appropriate but there's nothing to fix here.
> 
> I think Theo's problem is probably somewhere else, too --- apparently
> it's not so much that TransactionIdIsCurrentTransactionId takes a long
> time as that something is calling it lots of times with no check for
> interrupt.

Could it be something like heap_lock_tuple?  It calls MultiXactIdWait,
which calls GetMultXactIdMembers and TransactionIdIsCurrentTransactionId
on each member.  (heap_update and heap_delete do the same thing).  I
must admit I didn't read Theo's description on his scenario though.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support