I'm not sure if blocks reffered from all WAL records in single WAL
segment can fit kernel cache. This is why current pg_readahead
returns the last LSN and require starting LSN. So far, with FPW, it
seems that we can prefetch all the pages in a WAL segment. So it
will be okay for archive log compressed with pg_compresslog. I'll
test if it's okay in the case full_page_writes=off.
Anyway, I'd like to keep my proposal for 8.4 and continue the test and
evaluation to report to the mailing list.
I'll also change the whole code to run in the core.
-------
Koichi Suzuki
2008/10/29 Simon Riggs <simon@2ndquadrant.com>:
>
> On Wed, 2008-10-29 at 09:55 +0900, Koichi Suzuki wrote:
>
>> I'd like to hear some more about these. I'm more than happy to write
>> all the code inside PG core to avoid overhead to create another
>> process.
>
> Having an external program can help earlier releases also, so I think
> this is the right approach for now.
>
> In next PG release we should bring this into core, along with streaming.
>
> Interface would be better if it accepted
> pg_readahead filename
> or pg_readahead filename start-lsn
>
> We don't always need a starting lsn.
>
> --
> Simon Riggs www.2ndQuadrant.com
> PostgreSQL Training, Services and Support
>
>
--
------
Koichi Suzuki