MIME-Version: 1.0
References: 
 <CAHg+QDdKVnCLHot=AcoPpEiSyDzGz7wGYjAFHVOw57oDtmUDWQ@mail.gmail.com>
 <CAJpy0uDGM8eVqMORHKw61mm24AjH7jPZAhUaN3YeJrZ1bdpQFQ@mail.gmail.com>
 <CAHg+QDfQEX5b=4MB=67WgPrF4t8gyUMWyFp7-hFe=EAFW-qALA@mail.gmail.com>
 <CAJpy0uD8nmRCbhH1KBnb9Ch9SyxZh4OdeBaShBOkPKJM5A8Ujg@mail.gmail.com>
In-Reply-To: 
 <CAJpy0uD8nmRCbhH1KBnb9Ch9SyxZh4OdeBaShBOkPKJM5A8Ujg@mail.gmail.com>
From: Amit Kapila <amit.kapila16@gmail.com>
Date: Tue, 28 Apr 2026 16:28:29 +0530
Message-ID: 
 <CAA4eK1JutLSx2dAa7hFSmZxxqgWsAjk8GCwy4h85o9WEit3bpw@mail.gmail.com>
Subject: Re: [Patch]: Fix excessive ProcArrayLock acquisitions with
 subscription max_retention_duration=0
To: shveta malik <shveta.malik@gmail.com>
Cc: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: 
 <https://www.postgresql.org/message-id/CAA4eK1JutLSx2dAa7hFSmZxxqgWsAjk8GCwy4h85o9WEit3bpw%40mail.gmail.com>
Precedence: bulk

On Tue, Apr 28, 2026 at 9:38=E2=80=AFAM shveta malik <shveta.malik@gmail.co=
m> wrote:
>
> On Mon, Apr 27, 2026 at 10:32=E2=80=AFPM SATYANARAYANA NARLAPURAM
> <satyanarlapuram@gmail.com> wrote:
> >
> > Hi,
> >
> > On Mon, Apr 27, 2026 at 2:48=E2=80=AFAM shveta malik <shveta.malik@gmai=
l.com> wrote:
> >>
> >> On Mon, Apr 27, 2026 at 2:11=E2=80=AFPM SATYANARAYANA NARLAPURAM
> >> <satyanarlapuram@gmail.com> wrote:
> >> >
> >> > Hi Hackers,
> >> >
> >> > When a subscription has retain_dead_tuples enabled with maxretention=
 set
> >> > to zero (unlimited retention), adjust_xid_advance_interval() caps
> >> > xid_advance_interval to Min(interval, maxretention).  Since maxreten=
tion
> >> > is zero, this always collapses the interval to zero milliseconds.
> >> >
> >> > A zero makes  TimestampDifferenceExceeds(last_time, now, 0)  always
> >> > true in get_candidate_xid(). This causes the apply worker to call
> >> > GetOldestActiveTransactionId() on every single WAL message. This res=
ults in
> >> > a huge number of ProcArrayLock acquisitions under moderate write loa=
d.
> >> >
> >> > Fix by adding a maxretention > 0 guard to the cap. When maxretention=
 is zero ,
> >> > the exponential back-off in adjust_xid_advance_interval()
> >> > now works correctly, growing the interval from 100 ms toward the 180=
 s
> >> > ceiling.
> >> >
> >> > Measured with perf uprobe counting GetOldestActiveTransactionId call=
s
> >> > at ~39K TPS (pgbench, 5 clients):
> >> >
> >> >   Before fix: 25,104 calls / 5 s  (~5,021/s)
> >> >   After fix:     31 calls / 5 s  (~6/s)
> >> >
> >>
> >> Thanks for reporting it. I am reveiwing the problem sattement.
> >> Meanwhile can you please look at it, I am getting the following error
> >> while applying the patch on my Ubuntu setup (git am):
> >>
> >> error: corrupt patch at line 22
> >
> >
> > Thanks! Please find the updated v2 patch.
>
> Thanks. The patch looks good.
>

LGTM as well, so pushed.

--=20
With Regards,
Amit Kapila.