| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Kevin Grittner <kevin(dot)grittner(at)wicourts(dot)gov> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Florian Pflug <fgp(at)phlo(dot)org>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Catalog/Metadata consistency during changeset extraction from wal |
| Date: | 2012-06-25 20:04:10 |
| Message-ID: | 1340654533-sup-5535@alvh.no-ip.org |
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| Lists: | pgsql-hackers |
Excerpts from Kevin Grittner's message of lun jun 25 14:50:54 -0400 2012:
> One fine point regarding before and after images -- if a value
> doesn't change in an UPDATE, there's no reason to include it in both
> the BEFORE and AFTER tuple images, as long as we have the null
> column bitmaps -- or some other way of distinguishing unchanged from
> NULL. (This could be especially important when the unchanged column
> was a 50 MB bytea.)
Yeah, probably the best is to have the whole thing in BEFORE, and just
send AFTER values for those columns that changed, and include the
'replace' bool array (probably packed as a bitmap), so that the update
can be trivially constructed at the other end just like in
heap_modify_tuple.
--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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