On 23.05.2013 07:55, Robert Haas wrote:
On Thu, May 23, 2013 at 7:10 AM, Heikki Linnakangas
<hlinnakan...@vmware.com> wrote:
1. Scan the WAL log of the old cluster, starting from the point where
the new cluster's timeline history forked off from the old cluster. For each
WAL record, make a note of the data blocks that are touched. This yields a
list of all the data blocks that were changed in the old cluster, after the
new cluster forked off.
Suppose that a transaction is open and has written tuples at the point
where WAL forks. After WAL forks, the transaction commits. Then, it
hints some of the tuples that it wrote. There is no record in WAL
that those blocks are changed, but failing to revert them leads to
data corruption.
Bummer, you're right. Hmm, if you have checksums enabled, however, we'll
WAL log a full-page every time a page is dirtied for setting a hint bit,
which fixes the problem. So, there's a caveat with pg_rewind; you must
have checksums enabled.
- Heikki
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