On 07/16/2018 04:54 AM, Stephen Frost wrote:
> Greetings,
>
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> I think that the right basic idea is to have a GUC that chooses between
>> the two implementations, but whether it can be set automatically is not
>> clear to me. Can initdb perhaps investigate what kind of filesystem the
>> WAL directory is sitting on, and set the default value from hard-wired
>> knowledge about that?
>
> Maybe.. but I think we'd still need a way to change it because people
> often start with their database system minimally configured (including
> having WAL in the default location of the data directory) and only later
> realize that was a bad idea and change it later. I wouldn't be at all
> surprised if that "change it later" meant moving it to a different
> filesystem, and having to re-initdb to take advantage of that would be
> particularly unfriendly.
>
I'm not sure the detection can be made sufficiently reliable for initdb.
For example, it's not that uncommon to do initdb and then move the WAL
to a different filesystem using symlink. Also, I wonder how placing the
filesystem on LVM with snapshotting (which kinda makes it CoW) affects
the system behavior.
But maybe those are not issues, as long as the result is predictable.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
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