Hi Scott,
Thaks for the clear answers!
Scott Carey wrote:
You must either increase the memory that ZFS uses, or increase
Postgresql shard_mem and work_mem to get the aggregate of the two to
use more RAM.
I believe, that you have not told ZFS to reserve 8GB, but rather told
it to limit itself to 8GB.
That is correct, but since it will use the whole 8 GB anyway, I can just
as easily say that it will reseve that memory ;)
Some comments below:
On Thu, Oct 30, 2008 at 8:15 AM, Christiaan Willemsen
<[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> wrote:
Hi there,
I configured OpenSolaris on our OpenSolaris Machine. Specs:
2x Quad 2.6 Ghz Xeon
64 GB of memory
16x 15k5 SAS
If you do much writing, and even moreso with ZFS, it is critical to
put the WAL log on a different ZFS volume (and perhaps disks) than the
data and indexes.
I already did that. I also have a separate disk pair for the ZFS intent log.
Are you counting both the memory used by postgres and the memory used
by the ZFS ARC cache? It is the combination you are interested in,
and performance will be better if it is biased towards one being a
good chunk larger than the other. In my experience, if you are doing
more writes, a larger file system cache is better, if you are doing
reads, a larger postgres cache is better (the overhead of calling
read() in 8k chunks to the os, even if it is cached, causes CPU use to
increase).
No, the figure I gave is this is without the ARC cache.
If you do very large aggregates, you may need even 1GB on work_mem.
However, a setting that high would require very careful tuning and
reduction of space used by shared_buffers and the ZFS ARC. Its
dangerous since each connection with a large aggregate or sort may
consume a lot of memory.
Well, some taks may need a lot, but I guess most wil do fine with the
settings we used right now.
So It looks like I can tune the ARC to use more memory, and also
increase shared_mem to let postgres cache more tables?
