| From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | 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 00:56:59 |
| Message-ID: | CAB7nPqRsU2sB3Q6y4TTUkv6zPTh_fn6WvO_peEm+sVVL_TMGrQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
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.
--
Michael
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