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. Thank you! -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services