Re: Query is over 2x slower with jit=on

Hi,

On 2018-09-10 15:42:55 +0530, Amit Khandekar wrote:
> Attached is a patch that accumulates the per-worker jit counters into
> the leader process.

Thanks!

> I think we better show per-worker jit info also. The current patch
> does not show that. I think it would be easy to continue on the patch
> to show per-worker info also. Under the Gather node, we can show
> per-worker jit counters. I think this would be useful too, besides the
> cumulative figures in the leader process. Comments ?

Yes, I think that'd be good. I think we either should print the stats at
the top level as $leader_value, $combined_worker_value, $total_value or
just have the $combined_worker_value at the level where we print other
stats from the worker, too.

> /*
> + * Add up the workers' JIT instrumentation from dynamic shared memory.
> + */
> +static void
> +ExecParallelRetrieveJitInstrumentation(PlanState *planstate,
> + SharedJitInstrumentation *shared_jit)
> +{
> + int n;
> + JitContext *jit = planstate->state->es_jit;
> +
> + /* If the leader hasn't yet created a jit context, allocate one now. */
> + if (!jit)
> + {
> + planstate->state->es_jit = jit =
> + jit_create_context(planstate->state->es_jit_flags);
> + }

Wouldn't it be better to move the jit instrumentation to outside of the
context, to avoid having to do this? Or just cope with not having
instrumentation for the leader in this case? We'd kinda need to deal
with failure to create one anyway?

Greetings,

Andres Freund