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Re: WAL logging of heap_mark4update

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: WAL logging of heap_mark4update
Date: 2005-01-15 21:48:56
Message-ID: 12138.1105825736@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl> writes:
> Hackers,
> In access/heap/heapam.c, in heap_mark4update(), there's a comment that
> states

> 	/*
> 	 * XLOG stuff: no logging is required as long as we have no
> 	 * savepoints. For savepoints private log could be used...
> 	 */

> Is this still true in light of 8.0's savepoints?

It isn't.  Since mark4update is simply establishing a lock, which isn't
going to be held across a system crash anyway, I see no need to WAL-log
it.  (But hmmm ... to support 2PC we'd probably need to do so ...)

> I think the comment was made assuming that savepoints would be
> implemented using REDO,

I think the same.

> In any case I'm contemplating changing exclusive row locks to use
> LockAcquire, and supporting shared row locks using the same mechanism.
> All this per previous discussion on -hackers.  We could get rid of
> heap_mark4update if that's done, right?

Right.  The 2PC connection is another reason to do it that way --- 2PC
would require some way to save locks anyhow, and it'd be nice if there
were only one mechanism to deal with not two.

			regards, tom lane

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