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

Vitaly Davydov <v.davydov@postgrespro.ru>

From: "Vitaly Davydov" <v.davydov@postgrespro.ru>

To: "pgsql-hackers" <pgsql-hackers@postgresql.org>

Date: 2025-03-03T15:12:12Z

Lists: pgsql-hackers

Commits

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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

Attachments

0001-Keep-WAL-segments-by-slot-s-flushed-restart-LSN.patch (text/x-patch) patch 0001
0002-Fix-src-recovery-t-001_stream_rep.pl.patch (text/x-patch) patch 0002

Dear Hackers,

Let me please introduce a new version of the patch.

Patch description:

The slot data is flushed to the disk at the beginning of checkpoint. If
an existing slot is advanced in the middle of checkpoint execution, its
advanced restart LSN is taken to calculate the oldest LSN for WAL
segments removal at the end of checkpoint. If the node is restarted just
after the checkpoint, the slots data will be read from the disk at
recovery with the oldest restart LSN which can refer to removed WAL
segments.
    
The patch introduces a new in-memory state for slots -
flushed_restart_lsn which is used to calculate the oldest LSN for WAL
segments removal. This state is updated every time with the current
restart_lsn at the moment, when the slot is saving to disk.

With best regards,
Vitaly