On Wed, Apr 22, 2015 at 3:01 PM, Heikki Linnakangas <hlinn...@iki.fi> wrote: > On 04/22/2015 09:30 PM, Robert Haas wrote: >> On Wed, Apr 22, 2015 at 2:17 AM, Heikki Linnakangas <hlinn...@iki.fi> >> wrote: >>> >>> Note that it's a bit complicated to set up that scenario today. Archiving >>> is >>> never enabled in recovery mode, so you'll need to use a custom cron job >>> or >>> something to maintain the archive that C uses. The files will not >>> automatically flow from B to the second archive. With the patch we're >>> discussing, however, it would be easy: just set archive_mode='always' in >>> B. >> >> >> Hmm, I see. But if C never replays the last, partial segment from the >> old timeline, how does it follow the timeline switch? > > At timeline switch, we copy the old segment to the new timeline, and start > writing where we left off. So the WAL from the old timeline is found in the > segment nominally belonging to the new timeline.
Check. > For example, imagine that perform point-in-time recovery to WAL position > 0/1237E568, on timeline 1. That falls within segment > 000000010000000000000012. Then we end recovery, and switch to timeline 2. > After the switch, and some more WAL-logged actions, we'll have these files > in pg_xlog: > > 000000010000000000000011 > 000000010000000000000012 > 000000020000000000000012 > 000000020000000000000013 > 000000020000000000000014 Is the 000000010000000000000012 file a "partial" segment of the sort you're proposing to no longer achive? > Note that there are two segments ending in "12". They both have the same > point up to offset 0x37E568, corresponding to the switch point 0/1237E568. > After that, the contents diverge: the segment on the new timeline contains a > checkpoint/end-of-recovery record at that point, followed by new WAL > belonging to the new timeline. Check. > Recovery knows about that, so that if you set recovery target to timeline 2, > and it needs the WAL at the beginning of segment 12 (still belonging to > timeline 1), it will try to restoring both "000000010000000000000012" and > "000000020000000000000012". What if you set the recovery target to timeline 3? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
