slow "select count(*) from information_schema.tables;" in some cases

Hi

Sometimes simple sql's like this takes a very long time "select count(*) from information_schema.tables;"

Other sql's not including system tables may work ok but login also takes a very long time.

The CPU load on the server is around 25%. There is no iowait.

This happens typically when we are running many functions in parallel creating many temp tables and unlogged tables I think.

Here is a slow one:

https://explain.depesz.com/s/tUt5

and here is fast one :

https://explain.depesz.com/s/yYG4

Here are my settings (the server has around 256 GB og memory) :

max_connections = 500

work_mem = 20MB

effective_cache_size = 96GB

effective_io_concurrency = 256

shared_buffers = 96GB

temp_buffers = 80MB

Any hints ?

Thanks .

Lars