Re: User concurrency thresholding: where do I look?

On Thu, 19 Jul 2007, Josh Berkus wrote:

> It's a TPCC-like workload, so heavy single-row updates, and the
> updates/inserts are what's being measured.

There's so much going on with a TPC-C kind of workload.  Has anyone ever
looked into quantifying scaling for more fundamental operations?  There
are so many places a complicated workload could get caught up that
starting there is hard.  I've found it's helpful to see the breaking
points for simpler operations, then compare how things change as each new
transaction element is introduced.

As an example, take a look at the MySQL SysBench tool:
http://sysbench.sourceforge.net/docs/

Specifically their "oltp" tests.  Note how you can get a handle on how
simple selects scale, then simple inserts, then updates, and so on.  The
only thing I've thought of they missed is testing a trivial operation that
doesn't even touch the buffer cache ('SELECT 1'?) that would let you
quantify just general connection scaling issues.

It seems to me that you could narrow the list of possible causes here much
more quickly if you had a good handle on the upper concurrency of
lower-level operations.

[Note:  it's possible to run SysBench against a PG database, but the code
is very immature.  Last time I tried there were plenty of crashes and
there seemed to be some transaction wrapping issues that caused deadlocks
with some tests.]

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD