On Mon, May 9, 2011 at 4:23 PM, Aren Cambre <aren@xxxxxxxxxxxxxx> wrote: > I have a multi-threaded app. It uses ~22 threads to query Postgres. > Postgres won't use more than 1 CPU core. The 22-threaded app only has 3% CPU > utilization because it's mostly waiting on Postgres. > Here's the details: > The app has a "main" thread that reads table A's 11,000,000 rows, one at a > time. The main thread spawns a new thread for each row in table A's data. > This new thread: > > Opens a connection to the DB. > Does some calculations on the data, including 1 to 102 SELECTs on table B. > With an INSERT query, writes a new row to table C. > Closes the connection. > Thread dies. Its data is garbage collected eventually. > > Physical/software details: > > Core i7 processor--4 physical cores, but OS sees 8 cores via hyper-threading > 7200 RPM 500 GB HDD > About 1/2 total RAM is free during app execution > Windows 7 x64 > Postgres 9.0.4 32-bit (32-bit required for PostGIS) > App is C# w/ .NET 4.0. PLINQ dispatches threads. Npgsql is Postgres > connection tool. > > At first, the app pounds all 8 cores. But it quickly tapers off, and only 1 > core that's busy. The other 7 cores are barely doing a thing. > Postgres has 9 open processes. 1 process was slamming that 1 busy core. The > other 8 Postgres processes were alive but idle. > Each thread creates its own connection. It's not concurrently shared with > the main thread or any other threads. I haven't disabled connection pooling; > when a thread closes a connection, it's technically releasing it into a pool > for later threads to use. > Disk utilization is low. The HDD light is off much more than it is on, and a > review of total HDD activity put it between 0% and 10% of total capacity. > The HDD busy indicator LED would regularly flicker every 0.1 to 0.3 seconds. > The app runs 2 different queries on table B. The 1st query is run once, the > 2nd query can be run up to 101 times. Table C has redundant indexes: every > column referenced in the SQL WHERE clauses for both queries are indexed > separately and jointly. E.g., if query X references columns Y and Z, there > are 3 indexes: > > An index for Y > An index for Z > An index for Y and Z > > Table C is simple. It has four columns: two integers, a varchar(18), and a > boolean. It has no indexes. A primary key on the varchar(18) column is its > only constraint. > A generalized version of my INSERT command for table C is: > INSERT INTO raw.C VALUES (:L, :M, :N, :P) > I am using parameters to fill in the 4 values. > I have verified table C manually, and correct data is being stored in it. > Several Google searches suggest Postgres should use multiple cores > automatically. I've consulted with Npgsql's developer, and he didn't see how > Npgsql itself could force Postgres to one core. > (See http://pgfoundry.org/pipermail/npgsql-devel/2011-May/001123.html.) > What can I do to improve this? Could I be inadvertently limiting Postgres to > one core? Are you sure you are really using > 1 connection? While your test is running, log onto postgres with psql and grab the output of pg_stat_activity a few times. What do you see? merlin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
