Sql on Evan Hoffman

The not-so-secret secret to Postgres performance

Mon, 07 Oct 2013 10:19:05 +0000

I manage a bunch of Postgres DBs and one of the things I almost always forget to do when setting up a new one is set the readahead up from the default of 256. I created this script and run it out of /etc/rc.local and sometimes cron it too. The 3 commands at the top are only really relevant on systems with “huge” memory - probably over 64 GB. We ran into some memory problems with CentOS 6 on a box with 128 GB ram which we ended up working around by reinstalling CentOS 5, but the /sys/kernel/mm/redhat_transparent_hugepage/ options below should fix them in 6.x (though we haven’t actually tried it on that DB, we haven’t seen any problems in other large DBs).

Problems with PostgreSQL 9.0 on CentOS 6.3 with a 2.6.32-series kernel

Tue, 25 Sep 2012 13:20:36 +0000

Note: this is cross-posted from the Yodle Tech Blog. We recently migrated our Postgres database to a significantly more powerful machine. While our existing server was doing okay load-wise, we were approaching 90% full on its Postgres volume. We’d also recently acquired an awesome new PureStorage SSD-based SAN and were excited to move our database onto it. For comparison, here are the the specs for the two systems:


	Old server	New server
Nickname	DB1	DB2
CPU	2x 6-core Xeon X5690 CPUs at 3.47GHz	2x 8-core E5-2690 CPUs at 2.90 GHz
Memory	96 GB 1333 MHz	128 GB 1600 MHz
Storage	- Dell PERC H800 SAS HBA - Dell MD1220 drive enclosure - 24x 15k RPM SAS drives configured in RAID 10	- QLogic QLE2562 dual-port 8 Gbit FC HBA - PureStorage SSD-based SAN
OS	CentOS 5.6 x86_64	CentOS 6.3 x86_64
Kernel	2.6.18-238.9.1.el5	2.6.32-279.2.1.el6.x86_64

As you can probably guess, moving from spinning disk onto SSD was the centerpiece of the upgrade. We’d tested the PureStorage system pretty extensively and used it in some secondary databases and seen some amazing improvements. We were excited to see how it would handle our production workload.

Graphing SSH dictionary attacks with HighCharts

Fri, 18 Nov 2011 14:06:03 +0000

After my 10-year-old basement Linux server died this week from a power outage, I took the sad step of giving up on it. It’s died before and I’ve patched it back together with a new power supply here or an addon PCI SATA card there, but I finally decided to throw in the towel since I had a newer old computer that had been idle for several years. The one that died was an Athlon K7 750 MHz with 512 MB ram. The new one is an Athlon 2 GHz (3200+) with 1 gig. For my uses, specs don’t really matter that much, but it’s nice to have more power for free.

PostgreSQL query to determine the largest tables in the database

Tue, 17 May 2011 10:25:32 +0000

A PostgreSQL query to see the largest tables on-disk in a given database and how large their indices are.