Question about different behaviour in pg_wal when archive_mode is set on or off

public inbox for [email protected]  
help / color / mirror / Atom feed

From: Arpad Kiss A <[email protected]>
To: [email protected] <[email protected]>
Subject: Question about different behaviour in pg_wal when archive_mode is set on or off
Date: Thu, 26 Jun 2025 11:59:13 +0000
Message-ID: <AS8P189MB148022F6C262DC2C83CDFE97A97AA@AS8P189MB1480.EURP189.PROD.OUTLOOK.COM> (raw)

Hi,

I'm trying to understand the relation between 'archive_mode', pg_wal directory, 'max_wal_size' and failover.

I'm running the kubernetes example from patroni (patroni 4.0.6)
When 'archive_mode: off', and I issue a couple of 'patronictl failover' commands I observe the following files pg_wal:
```
postgres@patronidemo-0:~/pgdata/pgroot/data/pg_wal$ ls
000000080000000000000017  00000008.history          00000009.history          0000000A.history        0000000B.history    0000000C.history
000000080000000000000018  000000090000000000000018  0000000A0000000000000018  0000000B0000000000000018      0000000C0000000000000018  archive_status
```
Our problem with this is that If I do a lot of failovers, lets say a 100, then there will be a 100 files ( from 000000080000000000000018, to 0000001C0000000000000018)
and during checkpoint it doesn't decrease, and can go way over max_wal_size.

Whereas if I set 'archive_mode: on', and 'archive_command: /bin/true'
```
postgres@patronidemo-0:~/pgdata/pgroot/data/pg_wal$ ls
0000000E000000000000001F        0000000E.history          0000000F.history                00000010.history        00000011.history
0000000E0000000000000020        0000000F0000000000000021  000000100000000000000022        000000110000000000000023      archive_status
0000000E0000000000000021.partial  0000000F0000000000000022  000000100000000000000023.partial  000000110000000000000024
```
In this latter case after a timeline id is incremented postgres creates a new file with an incremented seqno, and in this case the files get rotated out normally they don't go over max_wal_size

Can someone explain why the difference in behavior? Does postgres only use the seqno only to differentiate the wal files here? Why does postgres not rotate out files in the former case?

Many thanks,
 Arpi

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]
  Subject: Re: Question about different behaviour in pg_wal when archive_mode is set on or off
  In-Reply-To: <AS8P189MB148022F6C262DC2C83CDFE97A97AA@AS8P189MB1480.EURP189.PROD.OUTLOOK.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