Re: Newly created replication slot may be invalidated by checkpoint

Amit Kapila <amit.kapila16@gmail.com>

From: Amit Kapila <amit.kapila16@gmail.com>

To: Vitaly Davydov <v.davydov@postgrespro.ru>

Cc: "suyu.cmj" <mengjuan.cmj@alibaba-inc.com>, aekorotkov <aekorotkov@gmail.com>, tomas <tomas@vondra.me>, michael <michael@paquier.xyz>, "bharath.rupireddyforpostgres" <bharath.rupireddyforpostgres@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2025-09-24T11:20:55Z

Lists: pgsql-hackers

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Prevent invalidation of newly synced replication slots.
- 3243c0177efb 17.8 landed
- 919c9fa13cd0 18.2 landed
- 851f6649cc18 19 (unreleased) landed
Prevent invalidation of newly created replication slots.
- 3510ebeb0dfa 17.8 landed
- 24cce33c332a 16.12 landed
- aae05622a7cb 15.16 landed
- 7406df60569f 14.21 landed
- d3ceb20846e4 18.2 landed
- 006dd4b2e5b3 19 (unreleased) landed
Fix re-distributing previously distributed invalidation messages during logical decoding.
- 45c357e0e85d 17.6 cited
Keep WAL segments by the flushed value of the slot's restart LSN
- 2090edc6f32f 17.6 cited
Keep WAL segments by slot's last saved restart LSN
- ca307d5cec90 18.0 cited

On Tue, Sep 23, 2025 at 12:19 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Sep 17, 2025 at 4:19 PM Vitaly Davydov <v.davydov@postgrespro.ru> wrote:
> >
> > [1] 0001-Fix-invalidation-when-slot-is-created-during-checkpo.patch
> >
>
> - /* Calculate how many segments are kept by slots. */
> - keep = slotsMinReqLSN;
> + /*
> + * Calculate how many segments are kept by slots. Keep the wal using
> + * the minimal value from the current reserved LSN and the reserved LSN at
> + * the moment of checkpoint start (before CheckPointReplicationSlots).
> + */
> + keep = XLogGetReplicationSlotMinimumLSN();
> + if (!XLogRecPtrIsInvalid(slotsMinReqLSN))
> + keep = Min(keep, slotsMinReqLSN);
>
> Can we add why we need this additional calculation here?
>

I was thinking some more about this solution. Won't it lead to the
same problem if ReplicationSlotReserveWal() calls
ReplicationSlotsComputeRequiredLSN() after the above calculation of
checkpointer?

-- 
With Regards,
Amit Kapila.