Generally, adding extra memory won't improve I/O throughput (reduce I/O wait
times) unless the application characteristics are such that you get decent
benefits from readahead and caching to avoid buffer recycling trashing data
you are going to need soon. For database applications (where feasible) it
is obviously an advantage if you can fit the working data set in core memory,
utilizing it as a large write-through cache.
So... given that you are talking about a database here, I'd recommend someone
looking a bit at the database runtime profiling data (if your engine has any)
to see if it is indeed reading data more often than it ought to. Most DB
engines like to manage their own data buffers rather than depending on OS-level
IO buffers (and sometimes even use direct IO operations to avoid the OS messing
with buffering), and so extra memory will only help if you configure the DB
engine to use the extra memory.
Once satisfied that the DB engine is configured for optimal performance, tuning
the IO system may be needed as wel.
Kris
On Thu, Aug 17, 2006 at 10:23:13AM -0400, David Boyes wrote:
> > We're looking at some high I/O wait times for a certain database. One
> > engineer has suggested that we add memory to Linux to speed things up.
> I
> > don't see it. Does adding RAM to Linux help its I/O throughput?
>
> On Intel, maybe. I would doubt that it would have a large impact on Z.
>
> Can you tell how much space the QDIO buffer allocation is taking up?
> Increasing that allocation may be worth considering, since the SCSI code
> takes advantage of QDIO if possible. What does the SAN fabric report on
> link utilization, and is the link configured for multipathing?
>
> David Boyes
> Sine Nomine Associates
>
> ----------------------------------------------------------------------
> For LINUX-390 subscribe / signoff / archive access instructions,
> send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit
> http://www.marist.edu/htbin/wlvindex?LINUX-390
----------------------------------------------------------------------
For LINUX-390 subscribe / signoff / archive access instructions,
send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit
http://www.marist.edu/htbin/wlvindex?LINUX-390
