Re: checkpointer continuous flushing

On Thu, Jan 7, 2016 at 4:21 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2016-01-07 11:27:13 +0100, Fabien COELHO wrote:
> > I read your patch and I know what I want to try to have a small and
simple
> > fix. I must admit that I have not really understood in which condition
the
> > checkpointer would decide to close a file, but that does not mean that
the
> > potential issue should not be addressed.
>
> There's a trivial example: Consider three tablespaces and
> max_files_per_process = 2. The balancing can easily cause three files
> being flushed at the same time.
>

Won't the same thing can occur without patch in mdsync() and can't
we handle it in same way? In particular, I am referring to below code:

mdsync()

{

..

/*

* It is possible that the relation has been dropped or

* truncated since the fsync request was entered.

* Therefore, allow ENOENT, but only if we didn't fail

* already on this file. This applies both for

* _mdfd_getseg() and for FileSync, since fd.c might have

* closed the file behind our back.

*

* XXX is there any point in allowing more than one retry?

* Don't see one at the moment, but easy to change the

* test here if so.

*/

if (!FILE_POSSIBLY_DELETED(errno) ||

failures > 0)

ereport(ERROR,

(errcode_for_file_access(),

errmsg("could not fsync file \"%s\": %m",

path)));

else

ereport(DEBUG1,

(errcode_for_file_access(),

errmsg("could not fsync file \"%s\" but retrying: %m",

path)));
}

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com