2016-09-08 11:49 GMT+12:00 Jim Nasby <Jim.Nasby@xxxxxxxxxxxxxx>:
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On 9/7/16 6:10 PM, David Gibbons wrote:
That is NOT safe. The problem is it allows rsync to use mtime alone
to decide that a file is in sync, and that will fail if Postgres
writes to a file in the same second that the first rsync reads from
it (assuming Postgres writes after rsync reads). You need to add the
--checksum flag to rsync (which means it will still have to read
everything that's in /var/lib/pgsql).
The checksum flag as you mention is not performant,
Definitely not. :/
If this is a concern, you're much better using the *--modify-window *flag:
When comparing two timestamps, rsync treats the timestamps as being
equal if they differ by no more than the modify-window value. This is
normally 0 (for an exact match), but you may find it useful to set this
to a larger value in some situations.
Hence, rsync -va --modify-window=1 would remove your concern about a
same second race condition without forcing the sync to read through all
the files.
Very interesting and useful!
Cool! I'll use the rsync -va --modify-window=1 instead.
Thanks!
Patrick
