Hi, On Mon, Apr 13, 2009 at 7:21 PM, Guillaume Smet <guillaume.s...@gmail.com> wrote: > On Mon, Apr 13, 2009 at 7:52 AM, Fujii Masao <masao.fu...@gmail.com> wrote: >> 1. the trigger file containing "smart" is created. >> 2. pg_standby is executed. >> 2-1. nextWALfile is restored. >> 2-2. the trigger file is deleted because nextWALfile+1 doesn't exist. >> 3. the restored nextWALfile is applied. >> 4. pg_standby is executed again to restore nextWALfile+1. > > I don't think it should happen. IMHO, it's an acceptable compromise to > replay all the WAL files present when I created the trigger file. So > if I have the smart shutdown trigger file and I don't have any > nextWALfile+1, I can remove the trigger file and stop the recovery: > pg_standby won't be executed again after that, even if a nextWALfile+1 > appeared while replaying the previous WAL file.
The scenario which I described is not related to whether the nextWALfile+1 exists or not. To clarify the detail of it; If pg_standby restores nextWALfile, deletes the trigger file and exits with 1 (i.e. tell the end of recovery to the startup process), the startup process considers that pg_standby failed, and tries to read the nextWALfile in pg_xlog instead of the restored file named "RECOVERYXLOG". This is undesirable behavior because some transactions would be lost if nextWALfile in pg_xlog doesn't exist. So, exit(0) should be called when nextWALfile exists. On the other hand, if pg_standby restores the nextWALfile, deletes the trigger file and calls exit(0), the startup process replays the restored file and tries to read the nextWALfile+1 because it doesn't know if the nextWALfile is the last valid WAL file. So, pg_standby may be executed again even after the trigger file is deleted. Am I missing something? > That said, stupid question: do we have a way to know the nextWALfile+1 > name to test if it exists? nextWALfile is transmitted through the > restore_command API and I'm wondering if we can have nextWALfile+1 > name without changing the restore_command API. Probably Yes; the following three steps are required, I think. - Get the timeline, logid and segid from the name of the nextWALfile. - Increment the logid and segid pair using NextLogSeg macro. - Calculate the name of the nextWALfile+1 using XLogFileName macro. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
