public inbox for [email protected]
help / color / mirror / Atom feedFrom: SATYANARAYANA NARLAPURAM <[email protected]>
To: 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: Mon, 27 Apr 2026 10:02:41 -0700
Message-ID: <CAHg+QDfQEX5b=4MB=67WgPrF4t8gyUMWyFp7-hFe=EAFW-qALA@mail.gmail.com> (raw)
In-Reply-To: <CAJpy0uDGM8eVqMORHKw61mm24AjH7jPZAhUaN3YeJrZ1bdpQFQ@mail.gmail.com>
References: <CAHg+QDdKVnCLHot=AcoPpEiSyDzGz7wGYjAFHVOw57oDtmUDWQ@mail.gmail.com>
<CAJpy0uDGM8eVqMORHKw61mm24AjH7jPZAhUaN3YeJrZ1bdpQFQ@mail.gmail.com>
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.
Attachments:
[application/octet-stream] v2-0001-Fix-apply-worker-busy-loop-when-subscription-max_ret.patch (1.9K, 3-v2-0001-Fix-apply-worker-busy-loop-when-subscription-max_ret.patch)
download | inline diff:
From 18c4738ab100ea29966cedcabcd1de1645ff3578 Mon Sep 17 00:00:00 2001
From: Satya Narlapuram <[email protected]>
Date: Mon, 27 Apr 2026 16:53:37 +0000
Subject: [PATCH] Fix apply worker busy loop when subscription
max_retention_duration is zero
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 internal 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.
---
src/backend/replication/logical/worker.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 9f2a16b1..dd6fc38a 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -4997,9 +4997,10 @@ adjust_xid_advance_interval(RetainDeadTuplesData *rdt_data, bool new_xid_found)
/*
* Ensure the wait time remains within the maximum retention time limit
- * when retention is active.
+ * when retention is active. Skip this cap when maxretention is zero,
+ * which means unlimited retention (no timeout).
*/
- if (MySubscription->retentionactive)
+ if (MySubscription->retentionactive && MySubscription->maxretention > 0)
rdt_data->xid_advance_interval = Min(rdt_data->xid_advance_interval,
MySubscription->maxretention);
}
--
2.43.0
view thread (7+ messages) latest in thread
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: [email protected]
Cc: [email protected], [email protected], [email protected], [email protected]
Subject: Re: [Patch]: Fix excessive ProcArrayLock acquisitions with subscription max_retention_duration=0
In-Reply-To: <CAHg+QDfQEX5b=4MB=67WgPrF4t8gyUMWyFp7-hFe=EAFW-qALA@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox