Re: lwlock contention with SSI

Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> About a month ago, I told Kevin Grittner in an off-list conversation
> that I'd work on providing him with some statistics about lwlock
> contention under SSI. I then ran a benchmark on a 16-core,
> 64-hardware thread IBM server, testing read-only pgbench performance
> at scale factor 300 with 1, 8, and 32 clients (and an equal number of
> client threads).

I hate to say this when I know how much work benchmarking is, but I
don't think any benchmark of serializable transactions has very
much value unless you set any transactions which don't write to
READ ONLY. I guess it shows how a naive conversion by someone who
doesn't read the docs or chooses to ignore the advice on how to get
good performance will perform, but how interesting is that?

It might be worth getting TPS numbers from the worst-looking test
from this run, but with the read-only run done after changing
default_transaction_read_only = on. Some shops using serializable
transactions set that in the postgresql.conf file, and require that
any transaction which will be modifying data override it.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company