On Mon, Apr 19, 2021 at 11:44:05PM +0900, Fujii Masao wrote: > On 2021/04/19 8:36, Justin Pryzby wrote: > > Reviewing this change which was committed last year as > > 321fa6a4a26c9b649a0fbec9fc8b019f19e62289 > > > > On Fri, Jul 03, 2020 at 03:57:38PM +0900, Fujii Masao wrote: > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao > > > > <masao.fu...@oss.nttdata.com> napsal: > > > > > > > > Maybe there can be documented so enabling this option can have a > > > > negative impact on performance. > > > > > > Yes. What about adding either of the followings into the doc? > > > > > > Enabling this parameter may incur a noticeable performance penalty. > > > > > > or > > > > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially when a fewer kinds of queries are executed on many > > > concurrent connections. > > > > Something seems is wrong with this sentence, and I'm not sure what it's > > trying > > to say. Is this right ? > > pg_stat_statements users different spinlock for each kind of query. > So fewer kinds of queries many sessions execute, fewer spinlocks > they try to acquire. This may lead to spinlock contention and > significant performance degration. This is what the statement is > trying to say.
What does "kind" mean ? I think it means a "normalized" query or a "query structure". "a fewer kinds" is wrong, so I think the docs should say "a small number of queries" or maybe: > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially similar queries are run by many concurrent connections and > > > compete to update the same pg_stat_statements entry -- Justin
