Horton

Re: AdvanceXLInsertBuffer vs. WAL segment compressibility

Chapman Flack <chap@anastigmatix.net>

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From: Chapman Flack <chap@anastigmatix.net>
To: Heikki Linnakangas <hlinnaka@iki.fi>, Robert Haas <robertmhaas@gmail.com>, Bruce Momjian <bruce@momjian.us>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-07-03T14:13:03Z
Lists: pgsql-hackers 
On 07/03/2017 09:39 AM, Heikki Linnakangas wrote:

> The most straightforward solution would be to just clear each page with
> memset() in the loop. It's a bit wasteful to clear the page again, just
> after AdvanceXLInsertBuffer() has initialized it, but this isn't
> performance-critical.

An in that straightforward approach, I imagine it would suffice to
memset just the length of a (short) page header; the page content
is already zeroed, and there isn't going to be a switch at the very
start of a segment, so a long header won't be encountered ... will it?

-Chap

Commits

  1. Ensure that WAL pages skipped by a forced WAL switch are zero-filled.

  2. Improve scalability of WAL insertions.

  3. Move BKP_REMOVABLE bit from individual WAL records to WAL page headers.