On 04/22/2015 10:21 PM, Robert Haas wrote:
On Wed, Apr 22, 2015 at 3:01 PM, Heikki Linnakangas <hlinn...@iki.fi> wrote:
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?
If you did pure archive recovery, with no streaming replication
involved, then no. If it was created by streaming replication, and the
replication had not filled the whole segment yet, then yes, it would be
a partial segment.
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?
It depends how timeline 3 was created. If timeline 3 was forked off from
timeline 2, then recovery would find it. If it was forked off directly
from timeline 1, then no.
- Heikki
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