| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Compression of full-page-writes |
| Date: | 2013-08-30 06:05:38 |
| Message-ID: | CAM3SWZSWV7km5AMqtDMXOA8vWnfrCTX2XA6fr5wwnW2PTQLw0Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Aug 29, 2013 at 10:55 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> I suppose that the cost of the random I/O involved would
>> probably dominate just as with compress_backup_block = off. That said,
>> you've used an SSD here, so perhaps not.
>
> Oh, maybe my description was confusing. full_page_writes was enabled
> while running the benchmark even if compress_backup_block = off.
> I've not merged those two parameters yet. So even in
> compress_backup_block = off, random I/O would not be increased in recovery.
I understood it that way. I just meant that it could be that the
random I/O was so expensive that the additional cost of decompressing
the FPIs looked insignificant in comparison. If that was the case, the
increase in recovery time would be modest.
--
Peter Geoghegan
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