From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Mike Blackwell <mike(dot)blackwell(at)rrd(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Peter Geoghegan <pg(at)heroku(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com> |
Subject: | Re: Performance Improvement by reducing WAL for Update Operation |
Date: | 2014-03-04 11:54:05 |
Message-ID: | 20140304115405.GA29018@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-03-04 12:43:48 +0200, Heikki Linnakangas wrote:
> >>This ought to be tested with the new logical decoding stuff as it modified
> >>the WAL update record format which the logical decoding stuff also relies,
> >>but I don't know anything about that.
> >
> >Hm, I think all it needs to do disable delta encoding if
> >need_tuple_data (which is dependent on wal_level=logical).
>
> That's a pity, but we can live with it.
Agreed. This is hardly the first optimization that only works for some
wal_levels.
> If we did this at a higher level and
> checked which columns have been modified, we could include just the modified
> fields in the record, which should to be enough for logical decoding. It
> might be even more useful for logical decoding too to know exactly which
> fields were changed.
Yea, I argued that way elsewhere in this thread. I do think we're going
to need per column info for further features in the near future. It's a
bit absurd that we're computing various sets of changed columns (HOT,
key, identity) plus the pre/postfix with this patchset.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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