Re: Clean shutdown and warm standby

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