On Tue, Jan 15, 2013 at 11:05 PM, Heikki Linnakangas <hlinnakan...@vmware.com> wrote: > Now that a standby server can follow timeline switches through streaming > replication, we should do teach pg_receivexlog to do the same. Patch > attached. > > I made one change to the way START_STREAMING command works, to better > support this. When a standby server reaches the timeline it's streaming from > the master, it stops streaming, fetches any missing timeline history files, > and parses the history file of the latest timeline to figure out where to > continue. However, I don't want to parse timeline history files in > pg_receivexlog. Better to keep it simple. So instead, I modified the > server-side code for START_STREAMING to return the next timeline's ID at the > end, and used that in pg_receivexlog. I also modifed BASE_BACKUP to return > not only the start XLogRecPtr, but also the corresponding timeline ID. > Otherwise we might try to start streaming from wrong timeline if you issue a > BASE_BACKUP at the same moment the server switches to a new timeline. > > When pg_receivexlog switches timeline, what to do with the partial file on > the old timeline? When the timeline changes in the middle of a WAL segment, > the segment old the old timeline is only half-filled. For example, when > timeline changes from 1 to 2, you'll have this in pg_xlog: > > 000000010000000000000006 > 000000010000000000000007 > 000000010000000000000008 > 000000020000000000000008 > 00000002.history > > The segment 000000010000000000000008 is only half-filled, as the timeline > changed in the middle of that segment. The beginning portion of that file is > duplicated in 000000020000000000000008, with the timeline-changing > checkpoint record right after the duplicated portion. > > When we stream that with pg_receivexlog, and hit the timeline switch, we'll > have this situation in the client: > > 000000010000000000000006 > 000000010000000000000007 > 000000010000000000000008.partial > > What to do with the partial file? One option is to rename it to > 000000010000000000000008. However, if you then kill pg_receivexlog before it > has finished streaming a full segment from the new timeline, on restart it > will try to begin streaming WAL segment 000000010000000000000009, because it > sees that segment 000000010000000000000008 is already completed. That'd be > wrong.
Can't we rename .partial file safely after we receive a full segment of the WAL file with new timeline and the same logid/segmentid? Regards, -- Fujii Masao -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
