On 01/09/2017 01:10 PM, Tom DalPozzo wrote:
Reread your original post and realized you where also asking
about transaction consistency and WALs. The thumbnail version is
that Postgres writes transactions to the WALs before they are
written to the data files on disk. A checkpoint represents a
point in the sequence when is is known that the changes recorded
in the WAL have been also recorded in the disk data files. So
Postgres then knows that in a recovery scenario it needs to only
redo/replay the WAL changes that are past the last checkpoint.
So the transactions are there it is just a matter of if they
need to be replayed or not. This is subject to caveats:
https://www.postgresql.org/docs/9.5/static/wal-reliability.html
<https://www.postgresql.org/docs/9.5/static/wal-reliability.html>
Hi, I had already read that doc but I can't answer clearly to my
questions 2,4 and 5.
The answer would seem to depend on what you consider 'a consistency
state position'. Is it possible to be more explicit about what you mean?
Regards
Pupillo
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Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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