Hi, On 2024-07-03 18:47:15 +0900, Michael Paquier wrote: > While looking at a different patch from Tristan in this area at [1], I > still got annoyed that this patch set was not able to support the case > of custom fixed-numbered stats, so as it is possible to plug in > pgstats things similar to the archiver, the checkpointer, WAL, etc. > These are plugged in shared memory, and are handled with copies in the > stats snapshots. After a good night of sleep, I have come up with a > good solution for that, among the following lines:
> - PgStat_ShmemControl holds an array of void* indexed by > PGSTAT_NUM_KINDS, pointing to shared memory areas allocated for each > fixed-numbered stats. Each entry is allocated a size corresponding to > PgStat_KindInfo->shared_size. I am dubious this is a good idea. The more indirection you add, the more expensive it gets to count stuff, the more likely it is that we end up with backend-local "caching" in front of the stats system. IOW, I am against making builtin stats pay the price for pluggable fixed-numbered stats. It also substantially reduces type-safety, making it harder to refactor. Note that you had to add static casts in a good number of additional places. Greetings, Andres Freund
