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Commitde8b098

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Document restrictions regarding incremental backups and standbys.
If you try to take an incremental backup on a standby and there hasn'tbeen much system activity, it might fail. Document why this happens.Also add a hint to the error message you get, to make it more likelythat users will understand what has gone wrong.Laurenz Albe and Robert HaasDiscussion:https://postgr.es/m/5468641ad821dad7aa3b2d65bf843146443a1b68.camel@cybertec.at
1 parent6622da8 commitde8b098

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‎doc/src/sgml/backup.sgml

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@@ -925,6 +925,17 @@ test ! -f /mnt/server/archivedir/00000001000000A900000065 && cp pg_wal/0
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to manage. For a large database all of which is heavily modified,
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incremental backups won't be much smaller than full backups.
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</para>
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<para>
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An incremental backup is only possible if replay would begin from a later
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checkpoint than for the previous backup upon which it depends. If you
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take the incremental backup on the primary, this condition is always
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satisfied, because each backup triggers a new checkpoint. On a standby,
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replay begins from the most recent restartpoint. Therefore, an
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incremental backup of a standby server can fail if there has been very
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little activity since the previous backup, since no new restartpoint might
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have been created.
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</para>
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</sect2>
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<sect2 id="backup-lowlevel-base-backup">

‎src/backend/backup/basebackup_incremental.c

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@@ -441,7 +441,8 @@ PrepareForIncrementalBackup(IncrementalBackupInfo *ib,
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errmsg("manifest requires WAL from final timeline %u ending at %X/%X, but this backup starts at %X/%X",
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range->tli,
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LSN_FORMAT_ARGS(range->end_lsn),
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LSN_FORMAT_ARGS(backup_state->startpoint))));
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LSN_FORMAT_ARGS(backup_state->startpoint)),
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errhint("This can happen for incremental backups on a standby if there was little activity since the previous backup.")));
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}
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else
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{

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