Re: Swappiness setting on a linux pg server

[Tobias Brox <tobias(at)nordicbet(dot)com>]

[Jim C. Nasby - Thu at 11:31:26AM -0500]
> The issue with pg_xlog is you don't need bandwidth... you need super-low
> latency. The best way to accomplish that is to get a battery-backed RAID
> controller that you can enable write caching on. In fact, if the
> controller is good enough, you can theoretically get away with just
> building one big RAID10 and letting the controller provide the
> low-latency fsyncs that pg_xlog depends on.

I was talking a bit about our system administrator.  We're running 4
disks in raid 1+0 for the database and 2 disks in raid 1 for the WALs
and for OS.  He wasn't really sure if we had write cacheing on the RAID
controller or not.  He pasted me some lines from the dmesg:

 sda: asking for cache data failed
 sda: assuming drive cache: write through
 failed line is expected from these controllers
 0000:02:0e.0 RAID bus controller: Dell PowerEdge Expandable RAID controller 4 (rev 06)

I think we're going to move system logs, temporary files and backup
files from the wal-disks to the db-disks.  Since our database aren't on
fire for the moment, I suppose we'll wait moving the rest of the OS :-)