From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Rahila Syed <rahilasyed90(at)gmail(dot)com>, Robert Haas <robertmhaas(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: | 2014-12-14 04:16:01 |
Message-ID: | 20141214041601.GA22463@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-12-14 09:56:59 +0900, Michael Paquier wrote:
> On Sun, Dec 14, 2014 at 5:45 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On 13 December 2014 at 14:36, 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.
> >
> > So we add 8 bytes to all FPWs, or only for compressed FPWs?
> In this case that was all. We could still use xl_info to put a flag
> telling that blocks are compressed, but it feels more consistent to
> have a way to identify if a block is compressed inside its own header.
Your 'consistency' argument doesn't convince me.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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