Re: Review of Refactoring code for sync node detection

Thanks for your review! (No worries for creating a new thread, I don't
mind as this is not a huge patch. I think you could have downloaded
the mbox from postgresql.org btw).

On Thu, Oct 30, 2014 at 8:24 AM, Jim Nasby <jim(at)nasby(dot)net> wrote:
> SyncRepGetSynchronousNode():
> IMHO, the top comment should mention that if there are multiple standbys of
> the same priority it returns the first one.
OK. Corrected.

> This switches from using a single if() with multiple conditions &&'d
> together to a bunch of if() continue's. I don't know if those will perform
> the same, and AFAIK this is pretty performance critical.
Well, we could still use the old notation with a single if(). That's
not much complicated to change.

> <grammarZealot>In the comments, "Process" should be
> "Proceed".</grammarZealot>
Noted. Thanks for correcting my Frenglish.

> pg_stat_get_wal_senders():
> The original version only loops through walsnds[] one time; the new code
> loops twice, both times while holding SyncRepLock(shared). This will block
> transaction commit if syncrep is enabled. That's not great, but presumably
> this function isn't going to be called terribly often, so maybe it's OK. (On
> a side note, perhaps we should add a warning to the documentation for
> pg_stat_replication warning not to hammer it...)
Hm. For code readability I did not really want to do so, but let's do
this: let's add a new argument in SyncRepGetSynchronousNode to
retrieve the priority of each WAL sender and do a single pass through
the array such as there is no performance difference.

Updated patch attached.
Regards,
--
Michael