Sean Chen <zyschen@gmail.com> wrote:
> Now from what you mentioned below, do you know what's the cost of
> postgres requesting new disk space from OS?
Depending on your OS and its version, your file system, your mount
options, and your disk subsystem (and its firmware revision), there
could be various effects -- the one likely to be biting you is write
barriers. When you allocate additional space from the OS, and it
extends a file or creates a new file, there might be a write barrier
to ensure that the file system catalog entries are persisted. This
could cause all writes (and possibly even reads) to pause until the
data is written to disk.
That's just a guess, of course. If you have a profiler you can run
you might be able to pin it down with that.
-Kevin