Purging Mirror Journal Files
Mirror journal files are subject to additional purge criteria because they must be successfully distributed by the primary failover member to the other mirror members and dejournaled on each to synchronize the mirrored databases (see Mirror Synchronization for a full description of this process). Transmission of the files to the backup is synchronous and always rapid when the mirror is operating normally, but transmission to asynchronous (async) members may take longer and may be delayed when an async is disconnected from the mirror. Backup and DR async members must also follow the same policy as the primary, since they are eligible to become primary in failover or disaster recovery situations. Mirror journal files are therefore purged as follows:
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On the primary failover member, a file is purged when the local journal file purge criteria have been met (see Configure Journal Settings) and when it has been received by the backup (if there is one) and all async members, whichever takes longer. If an async has been disconnected from the mirror for more than 14 days, however, files are purged even if that async has not yet received them.
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On the backup failover member (if there is one) and any disaster recovery (DR) async members, a file is purged when it has been fully dejournaled on that member, when local journal file purge criteria have been met, and when it has been received by all async members, with the same exception for asyncs that have been disconnected for more than 14 days.
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On reporting async members, mirror journal files are purged immediately after they have been dejournaled by default, to ensure that async mirror members do not run out of space (particularly when they are receiving journal files from multiple mirrors). You can optionally configure a reporting async to instead retain the files and purge them according to local journal file purge criteria; see Editing or Removing an Async Member.
No mirror journal file containing a currently open transaction is ever purged on any mirror member.
Note:
When a mirror journal file is retained longer than would be dictated by local journal file purge criteria, this is recorded in the member’s messages log and the reason is provided.
You can modify the defaults for purging mirror journal files with the SYS.Mirror.JrnPurgeDefaultWait()Opens in a new tab method.
