From: Robert Haas [mailto:robertmhaas@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
withfewer 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
toimprove shared buffers, WAL buffers, ProcArray, etc.
Regards
Takayuki Tsunakawa
