Thanks, as indicated we're using that right now. The 30% spinlock overhead unfortunately persists.
- Fsync was already disabled, too. Complete postgresql.conf used in testing: listen_addresses = '' max_connections = 2048 unix_socket_directories = '..' shared_buffers = 128MB log_line_prefix = '' synchronous_commit = 'off' wal_level = 'minimal' - linux perf report comparing schema-per-test vs database-per-test: https://ibb.co/CW5w2MW - Emiel On Mon, Feb 26, 2024 at 1:36 PM Pavel Stehule <pavel.steh...@gmail.com> wrote: > Hi > > po 26. 2. 2024 v 7:28 odesílatel Emiel Mols <em...@crisp.nl> napsal: > >> Hello, >> >> To improve our unit and end-to-end testing performance, we are looking to >> optimize initialization of around 500-1000 database *schemas* from a >> schema.sql file. >> >> Background: in postgres, you cannot change databases on >> existing connections, and using schemas would allow us to minimize the >> amount of active connections needed from our test runners, as we can reuse >> connections by updating search_path. In our current database-per-test setup >> we see that there is around a ~30% (!!) total CPU overhead in >> native_queued_spin_lock_slowpath (as profiled with linux perf), presumably >> because of the high connection count. We run ~200 tests in parallel to >> saturate a 128 core machine. >> >> In the schema-per-test setup, however, it becomes harder to cheaply >> create the schema. Before we could `create database test001 with template >> testbase` to set up the database for a test, and this was reasonably fast. >> Re-inserting a schema with ~500 table/index definitions across 500 test >> schema's is prohibitively expensive (around 1000ms per schema insertion >> means we're wasting 500 cpu-seconds, and there seems to be quite some lock >> contention too). Linux perf shows that in this setup we're reducing the >> native_queued_spin_lock_slowpath overhead to around 10%, but total test >> time is still slower due to all schema initialization being done. Also it >> feels quite elegant functions and types can be reused between tests. >> >> Does anyone have some insights or great ideas :)? Also pretty curious to >> the fundamental reason why having high/changing connection counts to >> postgres results in this much (spin)lock contention (or perhaps we're doing >> something wrong in either our configuration or measurements?). >> >> An alternative we haven't explored yet is to see if we can use pgbouncer >> or other connection pooler to mitigate the 30% issue (set limits so there >> are only ever X connections to postgres in total, and perhaps max Y per >> test/database). This does add another piece of infrastructure/complexity, >> so not really prefered. >> > > For testing > > a) use templates - CREATE DATABASE test TEMPLATE some; > > b) disable fsync (only for testing!!!) > > Regards > > Pavel > > >> Best, >> >> Emiel >> >
