From: Robert Haas [mailto:robertmh...@gmail.com] > My theory is that the number of wait events is NOT useful information, > or at least not nearly as useful the results of a sampling approach. > The data that LWLOCK_STATS produce are downright misleading -- they > lead you to think that the bottlenecks are in different places than > they really are, because the locks that produce the most waiting can > be 5th or 10th in terms of the number of wait events.
I understood you're saying that the number of waits alone does not necessarily indicate the bottleneck, because a wait with fewer counts but longer time can take a large portion of the entire SQL execution time. So, wait time is also useful. I think that's why Oracle describes and MySQL provides precise count and time without sampling. Haven't LOCK_STATS been helpful for PG developers? IIRC, it was used to pinpoint the bottleneck and evaluate the patch to improve shared buffers, WAL buffers, ProcArray, etc. Regards Takayuki Tsunakawa
