On Thu, Jan 2, 2025 at 3:58 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > I am wondering if the problem is not that the plan is slower, it's > that for some reason the planner took a lot longer to create it. > It's very plausible that partitionwise planning takes longer, and > maybe we have some corner cases where the time is O(N^2) or worse.
That doesn't seem like a totally unreasonable speculation, but it seems a little surprising that retaining the non-partitionwise paths would fix it. True, that might let us discard a bunch of partitionwise paths more quickly than would otherwise be possible, but I wouldn't expect that to have an impact as dramatic as what Jakub alleged. The thing I thought about was whether there might be some weird effects with lots of empty partitions; or maybe with some other property of the path like say sort keys or parallelism. For example if we couldn't generate a partitionwise path with sort keys as good as the non-partitionwise path had, or if we couldn't generate a parallel partitionwise path but we could generate a parallel non-partitionwise path. As far as I knew neither of those things are real problems, but if they were then I believe they could pretty easily explain a large regression. > However, this is pure speculation without a test case, and any > proposed fix would be even more speculative. I concur with your > bottom line: we should insist on a public test case before deciding > what to do about it. Yeah. -- Robert Haas EDB: http://www.enterprisedb.com
