Hello,
We recently brought online a new database cluster, and in the course
of ramping up traffic to it encountered a situation where a misplanned
query (analyzing helped with this, but I think the issue is still
relevant) resulted in that query being compiled with JIT, and soon a
large number of backends were running that same shape of query, all of
them JIT compiling it. Since each JIT compilation took ~2s, this
starved the server of resources.
There are a couple of issues here. I'm sure it's been discussed
before, and it's not the point of my thread, but I can't help but note
that the default value of jit_above_cost of 100000 seems absurdly low.
On good hardware like we have even well-planned queries with costs
well above that won't be taking as long as JIT compilation does.
But on the topic of the thread: I'd like to know if anyone has ever
considered implemented a GUC/feature like
"max_concurrent_jit_compilations" to cap the number of backends that
may be compiling a query at any given point so that we avoid an
optimization from running amok and consuming all of a servers
resources?
Regards,
James Coleman
