| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, 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: | 2014-12-15 18:46:14 |
| Message-ID: | CA+Tgmobvq_J1KQ5qbf9mYNO_yDw2FsSxNGzcTDDhgoGEuE8A_w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Dec 13, 2014 at 9:36 AM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> Something to be aware of btw is that this patch introduces an
> additional 8 bytes per block image in WAL as it contains additional
> information to control the compression. In this case this is the
> uint16 compress_len present in XLogRecordBlockImageHeader. In the case
> of the measurements done, knowing that 63638 FPWs have been written,
> there is a difference of a bit less than 500k in WAL between HEAD and
> "FPW off" in favor of HEAD. The gain with compression is welcome,
> still for the default there is a small price to track down if a block
> is compressed or not. This patch still takes advantage of it by not
> compressing the hole present in page and reducing CPU work a bit.
That sounds like a pretty serious problem to me.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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