Andreas Pflug wrote:
Heikki Linnakangas wrote:
No, no crash is involved. Just a normal server shutdown and start:
1. Server shutdown is initiated
2. A shutdown checkpoint is recorded at XLOG point 1234, redo ptr is
also 1234.
3. A XLOG_SWITCH record is written at 1235, right after the checkpoint
record.
4. The last round of archiving is done. The partial WAL file
containing the checkpoint and XLOG_SWITCH record is archived.
5. Postmaster exits.
6. Postmaster is started again. Since the system was shut down
cleanly, no WAL recovery is done. The WAL insert pointer is
initialized to right after the redo pointer, location 1235, which is
also the location of the XLOG_SWITCH record.
7. The next WAL record written will be written at 1235, overwriting
the XLOG_SWITCH record.
8. When the WAL file fills up, the system will try to archive the same
WAL file again, this time with additional WAL records that after the
checkpoint record.
So to get this down to a solution, it appears to be correct to execute
the RequestXLogSwitch right before CreateCheckPoint?
Hmm, then the checkpoint record isn't archived. That might be
acceptable, though, since all data would be safe in the preceding WAL.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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