Re: archived WALL files question

Frederiko Costa <frederiko@gmail.com> wrote:

> log files are being copied directly to the /mnt/data dir.
> However, the same segments are not in the pg_xlog
> dir. Is this a default behaviour?

Yes, the pg_xlog directory tries to keep a set of files ready to
receive WAL, and to hold it until the next checkpoint completes,
while the archive directory holds WAL files which have filled or
reached the archive_timeout limit.  There can be some overlap, but
basically you can view the archive as "past" and pg_xlog as
"future", with some potential overlap in "the present".

> Must I set archive_timeout?

No, but once a database write occurs, you don't have it backed up
until the WAL file is written to the archive directory.
archive_timeout is for those who want some wall-clock bounds on how
much they can lose in, say, a drive failure.  If the database can be
reloaded from some other source, or the data has no real value, it
may not pay to use this feature.

-Kevin