pá 11. 1. 2019 v 2:10 odesílatel Tsunakawa, Takayuki < tsunakawa.ta...@jp.fujitsu.com> napsal:
> 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. > the cumulated lock statistics maybe doesn't help with debugging - but it is very good indicator of database (in production usage) health. Regards Pavel > >
