On Mon, Nov 15, 2021 at 8:57 AM Mladen Gogala <gogala.mladen@xxxxxxxxx> wrote:
On 11/15/21 00:04, Pavel Stehule wrote:
Hi
There is a CentOS8-stream version which solves the problem but I cannot
use that in the office. I will probably have to wait for another month
before OL8 has everything that I need in its repositories. Now, the
question is what kind of an impact will running without llvm-jit have?
According to the links below, llvm-jit effects are quite spectacular:
https://llvm.org/devmtg/2016-09/slides/Melnik-PostgreSQLLLVM.pdf
https://www.pgcon.org/2017/schedule/events/1092.en.html
When JIT was used on very large query with a lot of CASE expr, then JIT has a positive effect about 50%. On usual large queries, the effect of JIT was about 20%. Unfortunately, JIT is sensitive to estimation, and the JIT sometimes increases seconds to queries, although without JIT this query is executed in ms. When you use a query that can be well calculated in parallel, then positive effect of JIT is less.
Regards
Pavel
Thanks Pavel, you answered my question. I'll wait with the upgrade.
FWIW, there was a lively discussion on the postgresql subreddit over the weekend on JIT: https://www.reddit.com/r/PostgreSQL/comments/qtsif5/cascade_of_doom_jit_and_how_a_postgres_update_led/
(lively for that subreddit anyway)
