Is there any material on how to benchmark Postgres meaningfully? I'm getting very frustrated with the numbers that `pgbench` is reporting:
-- allocating more resources to Postgres seems to be randomly dropping performance -- there seems to be no repeatability in the benchmarking numbers [1] -- there is no to figure out what is causing a bottleneck and which knob/setting is going to alleviate it. How do the PG wizards figure all this out? [1] https://dba.stackexchange.com/questions/227790/pgbench-20-30-variation-in-benchmark-results-non-repeatable-benchmarks -- Saurabh. On Thu, Jan 24, 2019 at 12:46 AM Saurabh Nanda <saurabhna...@gmail.com> wrote: > Hi, > > Please pardon me if this question is already answered in the > documentation, Wiki, or the mailing list archive. The problem is, that I > don't know the exact term to search for - I've tried searching for "linear > scalability" and "concurrency vs performance" but didn't find what I was > looking for. > > ## MAIN QUESTION > > pgbench -c 1 achieves approx 80 TPS > pgbench -c 6 should achieve approx 480 TPS, but only achieves 360 TPS > pgbench -c 12, should achieve approx 960 TPS, but only achieves 610 TPS > > If pgbench is being run on a 4c/8t machine and pg-server is being run on a > 6c/12t machine with 32GB RAM [1], and the two servers are connected with 1 > Gbit/s connection, I don't think either pgbench or pg-server is being > constrained by hardware, right? > > *In that case why is it not possible to achieve linear scalability, at > least till 12 concurrent connections (i.e. the thread-count of pg-server)?* > What is an easy way to identify the limiting factor? Is it network > connectivity? Disk IOPS? CPU load? Some config parameter? > > ## SECONDARY QUESTION > > *At what level of concurrent connections should settings like > shared_buffers, effective_cache_size, max_wal_size start making a > difference?* With my hardware [1], I'm seeing a difference only after 48 > concurrent connections. And that too it's just a 15-30% improvement over > the default settings that ship with the Ubuntu 18.04 package. Is this > expected? Isn't this allocating too many resources for too little gain? > > ## CONTEXT > > I am currently trying to benchmark PG 11 (via pgbench) to figure out the > configuration parameters that deliver optimum performance for my hardware > [1] and workload [2] > > Based on https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server > I've made the following relevant changes to the default PG config on Ubuntu > 18.04: > > max_connection=400 > work_mem=4MB > maintenance_work_mem=64MB > shared_buffers=12288MB > temp_buffers=8MB > effective_cache_size=16GB > wal_buffers=-1 > wal_sync_method=fsync > max_wal_size=5GB > autovacuum=off # NOTE: Only for benchmarking > > [1] 32 GB RAM - 6 core/12 thread - 2x SSD in RAID1 > [2] SaaS webapp -- it's a mixed workload which looks a lot like TPC-B > > Thanks, > Saurabh. > -- http://www.saurabhnanda.com
