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
