I pushed this patch -- 0001, 0002 and 0003 only. I did not include
anything from 0004 and 0005; I didn't even get to the point of reading
them, so that I could focus on the first part.
I did not find anything to complain about. I made a few adjustments and
asked David to supply a paragraph for perform.sgml (the "Using EXPLAIN"
section) which is included here. I also adopted Jesper's (actually
David's) suggestion of changing "Partitions Pruned" to "Partitions
Removed" in the EXPLAIN output.
I had reservations about a relation_open() in the new executor code. It
seemed a bit odd; we don't have any other relation_open in the executor
anywhere. However, setting up the pruneinfo needs some stuff from
relcache that I don't see a reasonable mechanism to pass through
planner. I asked Andres about it on IM and while he didn't endorse the
patch in any way, his quick opinion was that "it wasn't entirely
insane". I verified that we already hold lock on the relation.
While we didn't get fast pruning support for MergeAppend or the
DELETE/UPDATE parts, I think those are valuable and recommend to
resubmit those for PG12.
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services