Too many idle processes

Hello.
I have few Postgresql instances (version 9.6.*). 24 cores (load average 6-7)
installed pmm2-client(v.2.0.1) and OS debian ( version 8\9).

After some time with running postgres_exporter service i have see the idle processes in stat_activity.

SELECT /* pmm-agent:pgstatstatements */ "pg_catalog"."pg_user"."usesysid", "pg_catalog"."pg_user"."usename" FROM "pg_catalog"."pg_user" WHERE "pg_user"."usesysid" = $1 LIMIT 1

them count have increases with time . (Screen in attach)

Some params from postgres.conf

shared_preload_libraries = 'pg_stat_statements'
track_activity_query_size = 500
pg_stat_statements.track = top
track_io_timing=ON;

Please help to fix this problem