How does TRUNCATE differ from DELETE FROM <table>? Sorry, probably an easy RTFM question, but I'll ask anyhow. -----Original Message----- From: Samuel Stearns [mailto:SStearns@xxxxxxxxxxxxxxxx] Sent: Thursday, November 04, 2010 10:27 PM To: Jonathan Hoover; pgsql-admin@xxxxxxxxxxxxxx Cc: Kenneth Marshall Subject: RE: Disk Performance Problem on Large DB TRUNCATE removes all data from the table leaving the schema structure in place. What helped the most was probably the drop of the indexes. -----Original Message----- From: pgsql-admin-owner@xxxxxxxxxxxxxx [mailto:pgsql-admin-owner@xxxxxxxxxxxxxx] On Behalf Of Jonathan Hoover Sent: Friday, 5 November 2010 1:53 PM To: pgsql-admin@xxxxxxxxxxxxxx Cc: Kenneth Marshall Subject: Re: Disk Performance Problem on Large DB Just FYI, I removed the PK and the indexes for now. Load times for 1M rows is now 7 SECONDS instead of 7 MINUTES (or just never happening). Granted, I made the changes in #1 below, but WOW! So, question: what helped the most: 1) no PK, 2) no indexes, 3) the maintenance_work_mem being uncommented? I will test myself when I have time, but I'd like to know everyone's thoughts. Jon -----Original Message----- From: pgsql-admin-owner@xxxxxxxxxxxxxx [mailto:pgsql-admin-owner@xxxxxxxxxxxxxx] On Behalf Of Jonathan Hoover Sent: Thursday, November 04, 2010 10:03 PM To: pgsql-admin@xxxxxxxxxxxxxx Cc: Kenneth Marshall Subject: Re: Disk Performance Problem on Large DB 1. I have now set maintenance_work_mem to 256 MB (which was previously commented by the default config) 2. The version is PostgreSQL 8.1.18 on x86_64-redhat-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46) 3. What would be the best and cheapest thing I could for IO performance? 4. I need to read up on TRUNCATE, which I have not used before. Care to give a quick overview before I RTFM? Thanks, jon -----Original Message----- From: Kenneth Marshall [mailto:ktm@xxxxxxxx] Sent: Thursday, November 04, 2010 4:03 PM To: Jonathan Hoover Cc: pgsql-admin@xxxxxxxxxxxxxx Subject: Re: Disk Performance Problem on Large DB On Thu, Nov 04, 2010 at 01:42:49PM -0700, Jonathan Hoover wrote: > Hello, > > I have a RHEL 5 box, 4 GB RAM, single hard drive SATA, Intel Core 2 Duo 2.4. A basic workstation. > > I have a simple database, with one table for now. It has 4 columns: > > anid serial primary key unique, > time timestamp, > source varchar(5), > unitid varchar(15), > guid varchar(32) > > There is a btree index on each. > > I am loading data 1,000,000 (1M) rows at a time using psql and a COPY command. Once I hit 2M rows, my performance just drops out, and the next 1M never finishes. It takes 7 minutes for 1M rows to load. Once 2M are in there, I've waited an hour, and nothing. It doesn't seem to matter which 1M rows I try to load next, none ever finish. Each 1M rows is about 70MB on disk in the raw input file. > > I have "atop" installed, and it reports the drives at 100%, which it reports for the first 1M rows too. The MBw/s goes from 20+ on the first 2M rows, down to about 4 MBw/s or less now. The processor usage is at about 2 to 8% at this time (used by postgres). > > I have even waited for 1M rows to load, then done a vacuum for no good reason, then even restarted postgresql. I've made sure no disk or proc activity is happening before I start the next 1M rows. None of that seems to matter. > > I have a total of about 70M rows to load, but am at a standstill. I've read up on whatever performance docs I can find online, but I am not getting anywhere. > > I've increased shared_buffers to 256MB, and I've tried it with fsync commented out as per the default config. I've also tried it with fsync=off. No difference. > > Ideas? Thanks in advance, > Jon The initial 1M load if the table has just been truncated or created has no WAL logging. You can boost maintenance_work_mem to increase index creation/update performance. You are severely I/O limited and would be better off dropping your indexes during the load and re- creating them afterwards. If you are starting with an empty table, truncate it and then load all the data in a single transaction, all 7 COPY commands. Then COMMIT and build the indexes. Your question is also missing key information like config details, PostgreSQL version, ... Cheers, Ken -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
