From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Only first XLogRecData is visible to rm_desc with WAL_DEBUG |
Date: | 2014-03-25 00:13:14 |
Message-ID: | 20140325001314.GC9567@eldon.alvh.no-ip.org |
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Thread: | |
Lists: | pgsql-hackers |
Robert Haas wrote:
> On Mon, Mar 24, 2014 at 7:14 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> 3. Remove the feature altogether, so that enabling wal_debug doesn't
> >> cause all insertions to be logged anymore (no changes to the logging
> >> during replay). It's a lot less interesting now that we have pg_xlogdump.
> >
> > I think the main use-case for rm_desc anymore is making CONTEXT lines
> > for errors reported during WAL replay. I guess that situation does not
> > have the same problem, since we've already loaded the complete WAL record.
> >
> > However, I'm not sure how easy it's going to be for WAL_DEBUG to make the
> > data look the same as the replay case: in particular, substitution of
> > full-page-images for data would be tough to predict in advance (and moving
> > the printout into the critical section seems like a bad answer).
> >
> > I'd be okay with removing WAL_DEBUG, I think, particularly in view of the
> > fact that there have been no requests to make it a compiled-by-default
> > feature.
>
> I've found WAL_DEBUG quite useful in the past, when working on
> scalability, and have indeed wished for it to be
> compiled-in-by-default.
>
> I don't know whether I'm the only one, though.
You are not. I would rather have it fixed than removed, if possible. I
don't really care too much about getting a performance hit to palloc the
records, really; being able to actually read what's happening is much
more useful.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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