Re: fallocate / posix_fallocate for new WAL file creation (etc...)

Hi,

On 2013-05-15 16:26:15 -0500, Jon Nelson wrote:
> >> I have written up a patch to use posix_fallocate in new WAL file
> >> creation, including configuration by way of a GUC variable, but I've
> >> not contributed to the PostgreSQL project before. Therefore, I'm
> >> fairly certain the patch is not formatted properly or conforms to the
> >> appropriate style guides. Currently, the patch is based on 9.2, and is
> >> quite small in size - 3.6KiB.
>
> I have re-based and reformatted the code, and basic testing shows a
> reduction in WAL-file creation time of a fairly significant amount.
> I ran 'make test' and did additional local testing without issue.
> Therefore, I am attaching the patch. I will try to add it to the
> commitfest page.

Some where quick comments, without thinking about this:

* needs a configure check for posix_fallocate. The current version will
e.g. fail to compile on windows or many other non linux systems. Check
how its done for posix_fadvise.
* Is wal file creation performance actually relevant? Is the performance
of a system running on fallocate()d wal files any different?
* According to the man page posix_fallocate doesn't set errno but rather
returns the error code.
* I wonder whether we ever want to actually disable this? Afair the libc
contains emulation for posix_fadvise if the filesystem doesn't support
it.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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