On 9/28/16 10:32 PM, Michael Paquier wrote:
On Thu, Sep 29, 2016 at 7:45 AM, David Steele <da...@pgmasters.net> wrote:

In general I agree with the other comments that this could end up being
a problem.  On the other hand, since the additional locks are only taken
at checkpoint or archive_timeout it may not be that big a deal.

Yes, I did some tests on my laptop a couple of months back, that has 4
cores. After reducing NUM_XLOGINSERT_LOCKS from 8 to 4 to increase
contention and performing a bunch of INSERT using 4 clients on 4
different relations I could not catch a difference.. Autovacuum was
disabled to eliminate any noise. I tried checkpoint_segments at 30s to
see its effects, as well as larger values to see the impact with the
standby snapshot taken by the bgwriter. Other thoughts are welcome.

I don't have any better ideas than that.

+++ b/src/backend/postmaster/checkpointer.c
+                       /* OK, it's time to switch */
+                       elog(LOG, "Request XLog Switch");

LOG level seems a bit much here, perhaps DEBUG1?

That's from Horiguchi-san's patch, and those would be definitely
better as DEBUG1 by looking at it. Now and in order to keep things
simple I think that we had better discard this patch for now. I was
planning to come back to this thing anyway once we are done with the
first problem.

I still see this:

+++ b/src/backend/postmaster/checkpointer.c
                /* OK, it's time to switch */
+               elog(LOG, "Request XLog Switch");

Well for now attached are two patches, that could just be squashed into one.

Yes, I think that makes sense.

More importantly, there is a regression. With your new patch the xlogs are switching on archive_timeout again even with no changes. The v12 worked fine.

The differences are all in 0002-hs-checkpoints-v12-2.patch and as far as I can see the patch does not work correctly without these changes. Am I missing something?


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