On Wed, Jul 12, 2023 at 1:11 AM Dimitrios Apostolou <jimis@xxxxxxx> wrote: > So would it make sense for postgres to perform reads in bigger blocks? Is it > easy-ish to implement (where would one look for that)? Or must the I/O unit be > tied to postgres' page size? FYI as of last week we can do a little bit of that on the master branch: postgres=# select count(*) from t; preadv(46, ..., 8, 256237568) = 131072 preadv(46, ..., 5, 256368640) = 131072 preadv(46, ..., 8, 256499712) = 131072 preadv(46, ..., 5, 256630784) = 131072 postgres=# set io_combine_limit = '256k'; postgres=# select count(*) from t; preadv(47, ..., 5, 613728256) = 262144 preadv(47, ..., 5, 613990400) = 262144 preadv(47, ..., 5, 614252544) = 262144 preadv(47, ..., 5, 614514688) = 262144 Here's hoping the commits implementing this stick, for the PostgreSQL 17 release. It's just the beginning though, we can only do this for full table scans so far (plus a couple of other obscure places). Hopefully in the coming year we'll get the "streaming I/O" mechanism that powers this hooked up to lots more places... index scans and other stuff. And writing. Then eventually pushing the I/O into the background. Your questions actually triggered us to talk about why we couldn't switch a few things around in our project and get the I/O combining piece done sooner. Thanks!
