On Fri, May 17, 2024 at 5:55 AM Andres Freund <and...@anarazel.de> wrote: > > Hi, > > In the subthread at [1] I needed to trigger multiple rounds of index vacuuming > within one vacuum. > > It turns out that with the new dead tuple implementation, that got actually > somewhat expensive. Particularly if all tuples on all pages get deleted, the > representation is just "too dense". Normally that's obviously very good, but > for testing, not so much: > > With the minimum setting of maintenance_work_mem=1024kB, a simple table with > narrow rows, where all rows are deleted, the first cleanup happens after > 3697812 dead tids. The table for that has to be > ~128MB. > > Needing a ~128MB table to be able to test multiple cleanup passes makes it > much more expensive to test and consequently will lead to worse test coverage. > > I think we should consider lowering the minimum setting of > maintenance_work_mem to the minimum of work_mem.
+1 for lowering the minimum value of maintenance_work_mem. I've faced the same situation. Even if a shared tidstore is empty, TidStoreMemoryUsage() returns 256kB because it's the minimum segment size of DSA, i.e. DSA_MIN_SEGMENT_SIZE. So we can lower the minimum maintenance_work_mem down to 256kB, from a vacuum perspective. Regards, -- Masahiko Sawada Amazon Web Services: https://aws.amazon.com
