Re: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly

Dilip Kumar <dilipbalaut@gmail.com>

From: Dilip Kumar <dilipbalaut@gmail.com>

To: Alexander Korotkov <aekorotkov@gmail.com>

Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, Vitaly Davydov <v.davydov@postgrespro.ru>, Tom Lane <tgl@sss.pgh.pa.us>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, "tomas@vondra.me" <tomas@vondra.me>, vignesh C <vignesh21@gmail.com>

Date: 2025-06-27T04:17:19Z

Lists: pgsql-hackers

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Update comment for ReplicationSlot.last_saved_restart_lsn
- 0810fbb02dbe 19 (unreleased) landed
Fix CheckPointReplicationSlots() with max_replication_slots == 0
- 7195c804bd12 18.0 landed
Remove excess assert from InvalidatePossiblyObsoleteSlot()
- 70d8a91f82f1 18.0 landed
Improve runtime and output of tests for replication slots checkpointing.
- 5ed50f9386f0 17.6 landed
- 4464fddf7b50 18.0 landed
Keep WAL segments by slot's last saved restart LSN
- ca307d5cec90 18.0 landed
Fix an assert in CheckPointReplicationSlots().
- d1ffcc7fa3c5 17.0 cited

On Thu, Jun 26, 2025 at 3:20 AM Alexander Korotkov <aekorotkov@gmail.com> wrote:
>
> On Wed, Jun 25, 2025 at 11:25 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > On Wed, Jun 25, 2025 at 1:18 PM Hayato Kuroda (Fujitsu)
> > <kuroda.hayato@fujitsu.com> wrote:
> > > Another idea is to call ReplicationSlotsComputeRequiredLSN() when at least one
> > > of the restart_lsn is updated, like attached. I feel this could reduce the computation
> > > bit more.
> >
> > Right, that makes sense, if there is nothing updated on disk then we
> > can avoid computing this.
>
> Good idea.  But I think we should associate the "updated" flag
> directly to the fact that one slot (no matter logical or physical)
> changed its last_saved_restart_lsn.  See the attached patch.  I'm
> going to push it if no objections.
>

Looks good to me.


-- 
Regards,
Dilip Kumar
Google