Re: Compression of full-page-writes

On Fri, Aug 30, 2013 at 12:43 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> On Thu, Aug 29, 2013 at 7:55 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> [the amount of WAL generated during running pgbench]
>> 4302 MB (compress_backup_block = off)
>> 1521 MB (compress_backup_block = on)
>
> Interesting.
>
> I wonder, what is the impact on recovery time under the same
> conditions?

Will test! I can imagine that the recovery time would be a bit
longer with compress_backup_block=on because compressed
FPW needs to be decompressed.

> 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.

Regards,

--
Fujii Masao