Re: [PATCH] Add memory/disk usage for Function Scan nodes in EXPLAIN

Hi David,

> That doesn't seem great. On checking, I see Material has the same
> issue, but that's not been highlighted by the buildfarm members
> running debug_parallel_query = regress due to lack of EXPLAIN ANALYZE
> test that has a Material node. I've just posted a patch to fix that in
> [1]. Can you follow that code and resolve this issue in your patch?

Thanks for committing the Material patch! v4 Attached.
The main changes from v3 are:

- As is done for Material, each worker now copies its statistics into
shared memory in ExecEndFunctionScan(), and EXPLAIN ANALYZE shows them
per worker.

- I changed how the statistics are kept, so that the workers and EXPLAIN
use the same values. The tuplestore returned by
ExecMakeTableFunctionResult() already holds the whole result set of
the function and doesn't grow after that, so its statistics are taken
right after it's returned, and used to update the per-function maximum
and the node-level values. EXPLAIN just reads the leader's values, and
each worker copies its own into shared memory when it ends.

This made v3-0001's saving of the statistics before a rescan discards
the tuplestore, and moving FunctionScanPerFuncState into execnodes.h,
unnecessary, so I've merged the patches into one. The statistics are
only collected for EXPLAIN ANALYZE.

- Removed max_parallel_workers_per_gather = 0 from the tests. I've
confirmed make check passes with debug_parallel_query = regress too.

Regards,
Tatsuya Kawata