On Mon, Feb 17, 2025 at 2:41 PM Ron Johnson <ronljohnsonjr@xxxxxxxxx> wrote:
On Mon, Feb 17, 2025 at 4:36 PM Tom Lane <tgl@xxxxxxxxxxxxx> wrote:Ron Johnson <ronljohnsonjr@xxxxxxxxx> writes:
> The bigint "id" column in "mytbl" is populated from a sequence, and so is
> monotonically increasing: the newest records will have the biggest id
> values.
> The table also has a bytea column that averages about 100KB.
> Loading 200K rows is more than 200MB. I expected this "prewarm" statement
> to take much longer than 1/2 second. Am I still in the dark ages of
> computer speed, or is this statement not doing what I hope it's doing?
It's not pulling in the TOAST storage where the bytea column lives.
(pg_prewarm wouldn't have either, without special pushups.)Puzzling, since I ran "PERFORM *". What if I explicitly mentioned the bytea column's name?
It's more about the system optimizing away data retrieval because you've indicated you don't care about the contents due to using PERFORM. All it needs is a pointer to represent the future data, not the data itself. And PERFORM will never resolve that pointer by itself - so as Tom said your query would need to force pointer resolution by computing on the data.
David J.
