I built postgres (same version, 16.9) but --with-block-size=32 (I'd really love if this would be a initdb time flag!) and did some more testing:
synchronous_commit = off postgres@zerofs:~$ pgbench -vvv -c 100 -j 40 -t 10000 bench pgbench (16.9 (Ubuntu 16.10-1)) starting vacuum...end. starting vacuum pgbench_accounts...end. transaction type: <builtin: TPC-B (sort of)> scaling factor: 50 query mode: simple number of clients: 100 number of threads: 40 maximum number of tries: 1 number of transactions per client: 10000 number of transactions actually processed: 1000000/1000000 number of failed transactions: 0 (0.000%) latency average = 5.727 ms initial connection time = 59.223 ms tps = 17460.128835 (without initial connection time) synchronous_commit = on postgres@zerofs:/root$ pgbench -vvv -c 100 -j 40 -t 1000 bench pgbench (16.9 (Ubuntu 16.10-1)) starting vacuum...end. starting vacuum pgbench_accounts...end. transaction type: <builtin: TPC-B (sort of)> scaling factor: 50 query mode: simple number of clients: 100 number of threads: 40 maximum number of tries: 1 number of transactions per client: 1000 number of transactions actually processed: 100000/100000 number of failed transactions: 0 (0.000%) latency average = 301.800 ms initial connection time = 62.237 ms tps = 331.345391 (without initial connection time) ===================================== Then, using the same setup (same server, same postgres build), I create a ZeroFS NBD device with ext4 on top /dev/nbd0 on /mnt_9p type ext4 (rw,relatime,stripe=32) synchronous_commit = off postgres@zerofs:/mnt_9p$ pgbench -vvv -c 100 -j 40 -t 10000 bench pgbench (16.9 (Ubuntu 16.10-1)) starting vacuum...end. starting vacuum pgbench_accounts...end. transaction type: <builtin: TPC-B (sort of)> scaling factor: 50 query mode: simple number of clients: 100 number of threads: 40 maximum number of tries: 1 number of transactions per client: 10000 number of transactions actually processed: 1000000/1000000 number of failed transactions: 0 (0.000%) latency average = 3.615 ms initial connection time = 45.653 ms tps = 27665.373366 (without initial connection time) synchronous_commit = on postgres@zerofs:/root$ pgbench -vvv -c 100 -j 40 -t 1000 bench pgbench (16.9 (Ubuntu 16.10-1)) starting vacuum...end. starting vacuum pgbench_accounts...end. transaction type: <builtin: TPC-B (sort of)> scaling factor: 50 query mode: simple number of clients: 100 number of threads: 40 maximum number of tries: 1 number of transactions per client: 1000 number of transactions actually processed: 100000/100000 number of failed transactions: 0 (0.000%) latency average = 337.762 ms initial connection time = 43.969 ms tps = 296.066616 (without initial connection time) Best, Pierre On Fri, Jul 25, 2025, at 11:25, Pierre Barre wrote: > Hi, > > I went ahead and did that test. > > Here is the postgresql config I used for reference (note the wal > options (recycle, init_zero) as well as full_page_writes = off, because > ZeroFS cannot have torn writes by design). > > https://gist.github.com/Barre/8d68f0d00446389998a31f4e60f3276d > > Test was running on Azure with Standard D16ads v5 (16 vcpus, 64 GiB memory) > > This time, I didn't run ZFS with L2ARC, I just mounted ZeroFS with 9p. > > synchronous_commit = off > > postgres@zerofs:~$ pgbench -vvv -c 100 -j 40 -t 1000 bench > pgbench (16.9 (Ubuntu 16.9-0ubuntu0.24.04.1)) > starting vacuum...end. > starting vacuum pgbench_accounts...end. > transaction type: <builtin: TPC-B (sort of)> > scaling factor: 50 > query mode: simple > number of clients: 100 > number of threads: 40 > maximum number of tries: 1 > number of transactions per client: 1000 > number of transactions actually processed: 100000/100000 > number of failed transactions: 0 (0.000%) > latency average = 6.239 ms > initial connection time = 68.922 ms > tps = 16026.940646 (without initial connection time) > > > synchronous_commit = on > > postgres@zerofs:~$ pgbench -vvv -c 50 -j 15 -t 1000 bench > pgbench (16.9 (Ubuntu 16.9-0ubuntu0.24.04.1)) > starting vacuum...end. > starting vacuum pgbench_accounts...end. > transaction type: <builtin: TPC-B (sort of)> > scaling factor: 50 > query mode: simple > number of clients: 50 > number of threads: 15 > maximum number of tries: 1 > number of transactions per client: 1000 > number of transactions actually processed: 50000/50000 > number of failed transactions: 0 (0.000%) > latency average = 197.723 ms > initial connection time = 46.089 ms > tps = 252.878721 (without initial connection time) > > > Not great barebones with with synchronous_commit, but still usable! > > Best, > Pierre > > On Fri, Jul 25, 2025, at 00:44, Pierre Barre wrote: >>> This then begs the obvious question of how fast is this with >>> synchronous_commit = on? >> >> Probably not awful, especially with commit_delay. >> >> I'll try that and report back. >> >> Best, >> Pierre >> >> On Fri, Jul 25, 2025, at 00:03, Jeff Ross wrote: >>> On 7/24/25 13:50, Pierre Barre wrote: >>> >>>> It’s not “safe” or “unsafe”, there’s mountains of valid workloads which >>>> don’t require synchronous_commit. Synchronous_commit don’t make your >>>> system automatically safe either, and if that’s a requirement, there’s >>>> many workarounds, as you suggested, it certainly doesn’t make the setup >>>> useless. >>>> >>>> Best, >>>> Pierre >>>> >>>> On Thu, Jul 24, 2025, at 21:44, Nico Williams wrote: >>>>> On Fri, Jul 18, 2025 at 12:57:39PM +0200, Pierre Barre wrote: >>>>>> - Postgres configured accordingly memory-wise as well as with >>>>>> synchronous_commit = off, wal_init_zero = off and wal_recycle = off. >>>>> Bingo. That's why it's fast (synchronous_commit = off). It's also why >>>>> it's not safe _unless_ you have a local, fast, persistent ZIL device >>>>> (which I assume you don't). >>>>> >>>>> Nico >>>>> -- >>> This then begs the obvious question of how fast is this with >>> synchronous_commit = on?
