Re: Switching XLog source from archive to streaming when primary available
От | Nathan Bossart |
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Тема | Re: Switching XLog source from archive to streaming when primary available |
Дата | |
Msg-id | 20230112005114.GB2032194@nathanxps13 обсуждение исходный текст |
Ответ на | Re: Switching XLog source from archive to streaming when primary available (Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>) |
Ответы |
Re: Switching XLog source from archive to streaming when primary available
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Список | pgsql-hackers |
On Tue, Oct 18, 2022 at 07:31:33AM +0530, Bharath Rupireddy wrote: > In summary, the standby state machine in WaitForWALToBecomeAvailable() > exhausts all the WAL in pg_wal before switching to streaming after > failing to fetch from archive. The v8 patch proposed upthread deviates > from this behaviour. Hence, attaching v9 patch that keeps the > behaviour as-is, that means, the standby exhausts all the WAL in > pg_wal before switching to streaming after fetching WAL from archive > for at least streaming_replication_retry_interval milliseconds. I think this is okay. The following comment explains why archives are preferred over existing files in pg_wal: * When doing archive recovery, we always prefer an archived log file even * if a file of the same name exists in XLOGDIR. The reason is that the * file in XLOGDIR could be an old, un-filled or partly-filled version * that was copied and restored as part of backing up $PGDATA. With your patch, we might replay one of these "old" files in pg_wal instead of the complete version of the file from the archives, but I think that is still correct. We'll just replay whatever exists in pg_wal (which may be un-filled or partly-filled) before attempting streaming. If that fails, we'll go back to trying the archives again. Would you mind testing this scenario? -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
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