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help / color / mirror / Atom feedFrom: Nisha Moond <[email protected]>
To: SATYANARAYANA NARLAPURAM <[email protected]>
Cc: shveta malik <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Amit Kapila <[email protected]>
Subject: Re: [Patch]: Fix excessive ProcArrayLock acquisitions with subscription max_retention_duration=0
Date: Tue, 28 Apr 2026 14:03:48 +0530
Message-ID: <CABdArM5RtN5XUqE53LC+6FSKA1fFd1BHL5MmeX13pgmkN0Z=fA@mail.gmail.com> (raw)
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On Mon, Apr 27, 2026 at 10:32 PM SATYANARAYANA NARLAPURAM
<[email protected]> wrote:
>
> Hi,
>
> On Mon, Apr 27, 2026 at 2:48 AM shveta malik <[email protected]> wrote:
>>
>> On Mon, Apr 27, 2026 at 2:11 PM SATYANARAYANA NARLAPURAM
>> <[email protected]> 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 maxretention
>> > 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 results in
>> > a huge number of ProcArrayLock acquisitions under moderate write load.
>> >
>> > 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 calls
>> > 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 for the patch. I am able to reproduce the reported issue in
debugging. The xid_advance_interval stays 0 when retain_dead_tuples
is enabled but max_retention_duration is off which is unexpected
behavior.
Confirmed that the patch fixed it.
--
Thanks,
Nisha
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To: [email protected]
Cc: [email protected], [email protected], [email protected], [email protected], [email protected]
Subject: Re: [Patch]: Fix excessive ProcArrayLock acquisitions with subscription max_retention_duration=0
In-Reply-To: <CABdArM5RtN5XUqE53LC+6FSKA1fFd1BHL5MmeX13pgmkN0Z=fA@mail.gmail.com>
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