On 09/07/10 12:58, Mark Kirkwood wrote:
On 09/07/10 05:10, Josh Berkus wrote:
Simon, Mark,
Actually only 1 lock check per query, but certainly extra processing
and
data structures to maintain the pool information... so, yes certainly
much more suitable for DW (AFAIK we never attempted to measure the
additional overhead for non DW workload).
I recall testing it when the patch was submitted for 8.2., and the
overhead was substantial in the worst case ... like 30% for an
in-memory one-liner workload.
Interesting - quite high! However I recall you tested the initial
committed version, later additions dramatically reduced the overhead
(what is in the Bizgres repo *now* is the latest).
Purely out of interest, since the old repo is still there, I had a quick
look at measuring the overhead, using 8.4's pgbench to run two custom
scripts: one consisting of a single 'SELECT 1', the other having 100
'SELECT 1' - the latter being probably the worst case scenario. Running
1,2,4,8 clients and 1000-10000 tramsactions gives an overhead in the
5-8% range [1] (i.e transactions/s decrease by this amount with the
scheduler turned on [2]). While a lot better than 30% (!) it is
certainly higher than we'd like.
Cheers
Mark
[1] I got the same range for pgbench select-only using its usual workload
[2] As compared to Bizgres(8.2.4) and also standard Postgres 8.2.12.
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