Re: pg_resetwal with replication slot (17.11)

Dear Experts,
Is this mail list correct list to share my case,
If anybody gets this message and respond (to guide me to correct list), I really appreciate.

> On 21 Sep 2026, at 15:21, Rıdvan Korkmaz <serkan(dot)ridvan(dot)korkmaz(at)gmail(dot)com> wrote:
>
> Hi Dear Experts,
> I hit a case seems odd. I wonder if I do something unexpected, or something is here I can't see.
>
> First, these are all on test environment. The version is PostgreSQL 17.11, uses homebrew installation on MacOS.
>
> I have a master - replica setup, both are on the same host.
> master's
> PGDATA = m
> port = 15432
> rs = rep slot for streaming replication used by instance "r", created on master (m instance)
> max_wal_size = 4GB
> min_wal_size = 2GB
> wal_level = replica
>
>
> replica's
> PGDATA = r
> port = 25432
> primary_conninfo = created by pg_basebackup
> primary_slot_name = rs
>
>
> Case: I have 16MB WAL files on master instance (so on replica). I want to utilize 1GB WAL files.
> Here are the steps I take.
>
> 1. setup master - replica run on same host in respective directories and on ports
> 2. verify streaming replication works
> 3. verify "rs" (replication slot), master ("m" instance), and replica ("r" instance) have SAME WAL lsn
> 4. stop master, keep replica online (simulation for actual case) (pg_ctl-17 stop -D m)
> 5. run "pg_resetwal-17 -D m --wal-segsize=1024" on master instance.
> 6. start master instance, started, fine. Replica complains about "ERROR: requested WAL segment 000000010000000000000000 has already been removed", no worry.
> 7. stop master again, cool, done. (last log lines: "checkpoint complete", "database system is shut down")
> 8. start master -> bamm, could not start. (pg_ctl-17 start -D m -l m.log)
>
> There is no read, write between after step 3 (after verification of WAL lsns)
>
> Final failure log (step 8):
> 2026-09-21 14:47:45.525 +03 [22817] LOG: starting PostgreSQL 17.11 (Homebrew) on aarch64-apple-darwin25.6.0, compiled by Apple clang version 21.0.0 (clang-2100.1.1.101), 64-bit
> 2026-09-21 14:47:45.525 +03 [22817] LOG: listening on IPv4 address "127.0.0.1", port 15432
> 2026-09-21 14:47:45.525 +03 [22817] LOG: listening on Unix socket "/tmp/.s.PGSQL.15432"
> 2026-09-21 14:47:45.528 +03 [22820] LOG: database system was shut down at 2026-09-21 14:46:42 +03
> 2026-09-21 14:47:45.528 +03 [22820] LOG: invalid checkpoint record
> 2026-09-21 14:47:45.528 +03 [22820] PANIC: could not locate a valid checkpoint record at 0/40000110
> 2026-09-21 14:47:45.528 +03 [22817] LOG: startup process (PID 22820) was terminated by signal 6: Abort trap: 6
> 2026-09-21 14:47:45.528 +03 [22817] LOG: terminating any other active server processes
> 2026-09-21 14:47:45.529 +03 [22817] LOG: shutting down due to startup process failure
> 2026-09-21 14:47:45.529 +03 [22817] LOG: database system is shut down
>
>
>
> After pg_resetwal, first start of master successful, but a second start fails.
> I guess this causes master to be lost.
>
> I'm able to spot the issue:
> The issue is replication slot. If I would have removed replication slot before second start (do it between 6 and 7), it succeeds.
>
> Questions:
> 1. Is this behavior is expected?
> 2. Should replication slot case mentioned in PostgreSQL documents? (I checked yet could not see)
> 3. Am I doing something out of order, unexpected?
> 4. Once I understood the case, I dropped replication slot and able to start master. Now I want to copy m/global/pg_control to replica and m/pg_wal to replica as well and complete wal segment size change. I wonder if this way is documented or supported. I can say "it works" but does not mean "supported or documented at all".
>
> Thank you in advance.
>
> Attachments:
> <1-master-replica-setup-info.txt>
> <3-all-wal-lsn-same.txt>
>
>