On 2024-06-29 03:27, Peter Geoghegan wrote: > On Thu, Jun 27, 2024 at 11:06 PM <masahiro.ik...@nttdata.com> wrote: >> Although I haven't looked on your patch yet, if it's difficult to know >> how it can optimize during the planning phase, it's enough for me to just >> show "Skip Scan Cond (or Non-Key Filter)". This is because users can >> understand that inefficient index scans *may* occur. > > That makes sense. > > The goal of your patch is to highlight when an index scan is using an > index that is suboptimal for a particular query (a query that the user > runs through EXPLAIN or EXPLAIN ANALYZE). The underlying rules that > determine "access predicate vs. filter predicate" are not very > complicated -- they're intuitive, even. But even an expert can easily > make a mistake on a bad day. > > It seems to me that all your patch really needs to do is to give the > user a friendly nudge in that direction, when it makes sense to. You > want to subtly suggest to the user "hey, are you sure that the index > the plan uses is exactly what you expected?". Fortunately, even when > skip scan works well that should still be a useful nudge. If we assume > that the query that the user is looking at is much more important than > other queries, then the user really shouldn't be using skip scan in > the first place. Even a good skip scan is a little suspicious (it's > okay if it "stands out" a bit).
Yes, you're right. I'd like users to take the chance easily. -- Masahiro Ikeda NTT DATA CORPORATION
