| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Rahila Syed <rahilasyed90(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [REVIEW] Re: Compression of full-page-writes |
| Date: | 2014-12-12 18:51:03 |
| Message-ID: | CA+U5nM+MMiyVaHXG+aw2bp3BoxcKvPPLH1yghjkZ7mneCVejzA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 12 December 2014 at 18:04, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> Well, it seems we need to see some actual cases where compression does
> help before moving forward. I thought Amit had some amazing numbers for
> WAL compression --- has that changed?
For background processes, like VACUUM, then WAL compression will be
helpful. The numbers show that only applies to FPWs.
I remain concerned about the cost in foreground processes, especially
since the cost will be paid immediately after checkpoint, making our
spikes worse.
What I don't understand is why we aren't working on double buffering,
since that cost would be paid in a background process and would be
evenly spread out across a checkpoint. Plus we'd be able to remove
FPWs altogether, which is like 100% compression.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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