[nycbug-talk] Memory sizing
lists at stringsutils.com
Sat Apr 22 15:33:37 EDT 2006
Pete Wright writes:
> the best i'd look for info on memory utilization in freebsd would be the
> McKusick/Neville-Neil design and implementation book.
Althought that is a good long term plan I would settle for a good
explanation of top's memory display. :-)
I have found some, but not to the level I need.
In short I am looking to answer "does this machine has enough memory for the
amount of programs we are running it it.. and to leave a decent amount of
memory for the OS to cache files".
> text in general, and should help you get a handle on how FreeBSD in
> specific is going to utilize memory.
That is great to know.. but ultimately it comes down to.. does the machine
has too much running on it.
The first thing I look at is swap. If the machine is using tens of megabytes
from swap and you see the swap getting used frequently in top.. that is a
clear sign that machine has too many processes for the amount of RAM.
> what is the profile on queries you are going to running against the
I am looking to size two machines. One DB, one mail server.
For the DB a large percent of the load will be writes. The app that will
connect and the load programs are currently getting done and I don't have
numbers yet.. However from the existing system (using mysql) that the new
system will replace I see probably 90% + are writes with mostly relatively
simple (but large) queries. Queries like "show me all the records that
matchi this particular criteria and join a couple tables to expand codes".
>are we looking at lot's of small queries,periodic quries on large
> data set's or something in between.
Lots of inserts.
Unfrequent queries, but when they are done they will return very frequently
large number of recores. As far as I can tell it will always be index
> large postgres server that is going to be doing data warehousing, we are
> thinking that we should be fine with 4gig's or RAM as we will not have
> many concurrent connections.
I am a bit undecided between going SATA or SCSI.
To be more precise..
6 400GB disks on RAID 10
2 hot spares
Net usable: 1.2TB raw (before filesystem)
7.2K rpm disks
7 150GB disks on RAID5
1 hot spare
Net usable: 900GB raw (before filesystem)
4 GB RAM
10K rpm disks
There is also the 10K rpm SATA drives, but I don't think RAID5 with SATA may
be good enough.
>From what I am reading so far after 6 disks the performance between RAID10
and RAID5 is simmilar.
> if you are going to have many people hitting this thing, then yea i'd
> give it as much memory as practical and the fastest storage i can
Found a link on postgresql performance and they actually claim that disk
subsystem, them memory, then CPU is what matters.. Obviously as long as
there is a minimal/acceptable amount of RAM to begin with.
> as an aside, i have another postgres DB that we are running out of a
> memory FS.
Interesting. How big is the DB?
Can't wait to the days when solid state drives become cheaper. :-)
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