On 03.04.2013 22:50, Jeff Janes wrote:
On Wed, Apr 3, 2013 at 11:14 AM, Heikki Linnakangas<hlinnakan...@vmware.com
wrote:
On 03.04.2013 18:58, Jeff Janes wrote:
On Tue, Apr 2, 2013 at 10:08 PM, Jeff Janes<jeff.ja...@gmail.com> wrote:
This commit introduced a problem with wal_keep_segments:
commit dfda6ebaec6763090fb78b458a979b**558c50b39b
The problem seems to be that the underflow warned about is happening,
because the check to guard it was checking the wrong thing. However, I
don't really understand KeepLogSeg. It seems like segno, and hence
recptr,
don't actually serve any purpose.
Hmm, the check is actually correct, but the assignment in the else-branch
isn't. The idea of KeepLogSeg is to calculate recptr - wal_keep_segments,
and assign that to *logSegNo. But only if *logSegNo is not already< than
the calculated value. Does the attached look correct to you?
Let me describe what I think is going on. My description is "On start,
recptr is the redo location of the just-completed checkpoint, and logSegNo
is the redo location segment of the checkpoint before that one. We want to
keep the previous-checkpoint redo location, and we also want to keep
wal_keep_segments before the current-checkpoint redo location, so we take
whichever is earlier."
If my understanding is now correct, then I think your patch looks correct.
(Also, applying it fixed the problem I was having.)
Ok, thanks, applied.
Why do we keep wal_keep_segments before the just-finished checkpoint,
rather than keeping that many before the previous checkpoint? I seems like
it would be more intuitive (to the DBA) for that parameter to mean "keep
this many more segments than you otherwise would". I'm not proposing we
change it, I'm just curious about why it is done that way.
It feels more intuitive to me the way it is. wal_keep_log_segments means
"make sure there are always this many old WAL segments available in the
server, regardless of any other settings". If you have a standby, it
means that you don't need a new base backup as long as you don't fall
behind the master by more than wal_keep_segments segments.
On 03.04.2013 21:33, Alvaro Herrera wrote:
"by by"
Fixed, thanks.
- Heikki
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