From: | vignesh C <vignesh21(at)gmail(dot)com> |
---|---|
To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
Subject: | Re: Replication slot stats misgivings |
Date: | 2021-04-27 05:32:12 |
Message-ID: | CALDaNm3JNYvCyEYqy0MUwP99ye4hUisE0mEggURmZTA7WjSfbQ@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Tue, Apr 27, 2021 at 9:48 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
>
> On Tue, Apr 27, 2021 at 9:43 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Tue, Apr 27, 2021 at 9:17 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > On Tue, Apr 27, 2021 at 11:31 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > > >
> > > > > > And I think there is
> > > > > > also a risk to increase shared memory when we want to add other
> > > > > > statistics in the future.
> > > > > >
> > > > >
> > > > > Yeah, so do you think it is not a good idea to store stats in
> > > > > ReplicationSlot? Actually storing them in a slot makes it easier to
> > > > > send them during ReplicationSlotRelease which is quite helpful if the
> > > > > replication is interrupted due to some reason. Or the other idea was
> > > > > that we send stats every time we stream or spill changes.
> > > >
> > > > We use around 64 bytes of shared memory to store the statistics
> > > > information per slot, I'm not sure if this is a lot of memory. If this
> > > > memory is fine, then I felt the approach to store stats seems fine. If
> > > > that memory is too much then we could use the other approach to update
> > > > stats when we stream or spill the changes as suggested by Amit.
> > >
> > > I agree that makes it easier to send slot stats during
> > > ReplicationSlotRelease() but I'd prefer to avoid storing data that
> > > doesn't need to be shared in the shared buffer if possible.
> > >
> >
> > Sounds reasonable and we might add some stats in the future so that
> > will further increase the usage of shared memory.
> >
> > > And those
> > > counters are not used by physical slots at all. If sending slot stats
> > > every time we stream or spill changes doesn't affect the system much,
> > > I think it's better than having slot stats in the shared memory.
> > >
> >
> > As the minimum size of logical_decoding_work_mem is 64KB, so in the
> > worst case, we will send stats after decoding that many changes. I
> > don't think it would impact too much considering that we need to spill
> > or stream those many changes. If it concerns any users they can
> > always increase logical_decoding_work_mem. The default value is 64MB
> > at which point, I don't think it will matter sending the stats.
>
> Sounds good to me, I will rebase my previous patch and send a patch for this.
>
Attached patch has the changes to update statistics during
spill/stream which prevents the statistics from being lost during
interrupt.
Thoughts?
Regards,
Vignesh
Attachment | Content-Type | Size |
---|---|---|
v3-0001-Update-replication-statistics-after-every-stream-.patch | text/x-patch | 4.2 KB |
From | Date | Subject | |
---|---|---|---|
Next Message | Dilip Kumar | 2021-04-27 05:33:02 | Re: [BUG] "FailedAssertion" reported when streaming in logical replication |
Previous Message | Amul Sul | 2021-04-27 05:20:22 | Skip temporary table schema name from explain-verbose output. |