On Tue, Jan 21, 2025 at 09:52:51AM -0600, Nathan Bossart wrote: > On Tue, Jan 21, 2025 at 03:31:27AM +0000, Andy Fan wrote: >> 3. Why is the purpose of preallocated_segments directory? what in my >> mind is we just prellocate the normal filename so that XLogWrite could >> open it directly. This is same as what wal_recycle does and we can reuse >> the same strategy to clean up them if they are not needed anymore. > > The purpose is to limit the use of pre-allocated segments to only > situations where WAL recycling is not sufficient. Basically, if writing a > record would require a new segment to be created, we can quickly pull a > pre-allocated one instead of creating it ourselves. Besides simplifying > matters, this prevents a lot of unnecessary pre-allocation, since many > workloads will almost never need anything beyond the recycled segments.
That being said, it would be nice to avoid the fsync() overhead to move a pre-allocated WAL into place. My first instinct is that would be substantially more complicated and may not actually improve matters all that much, but I agree that it's worth exploring. -- nathan
