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Re: Improve XLOG_NO_TRAN related comments

From: Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Improve XLOG_NO_TRAN related comments
Date: 2005-12-25 21:44:41
Message-ID: Pine.LNX.4.58.0512251633340.28412@eon.cs (view raw, whole thread or download thread mbox)
Lists: pgsql-patches

On Sat, 24 Dec 2005, Tom Lane wrote:
> Removing these comments entirely, without changing the code they explain,
> doesn't strike me as an improvement.

I just checked if we can remove XLOG_NO_TRAN happily, and the conclusion
is that it could bring some benefits (though not much) to our system. The
key is the CheckpointStartLock lock. If we remove XLOG_NO_TRAN, then even
statement like this will block/wait checkpoint:

	SELECT nextval('serial');

Of course, we can add a test in XLogInsert() to solve this problem like

	no_tran == ((rmid == RM_XLOG_ID) || (rmid == RM_SEQ_ID) || ...)

But the better way is leave XLOG_NO_TRAN for now till we find a way to
avoid CheckpointStartLock lock.


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