Re: Benchmarking tools, methods

2011/11/18 Tomas Vondra <tv@fuzzy.cz>:
> On 18 Listopad 2011, 10:55, CSS wrote:
>> Hello,
>>
>> I'm going to be testing some new hardware (see
>> http://archives.postgresql.org/pgsql-performance/2011-11/msg00230.php) and
>> while I've done some very rudimentary before/after tests with pgbench, I'm
>> looking to pull more info than I have in the past, and I'd really like to
>> automate things further.
>>
>> I'll be starting with basic disk benchmarks (bonnie++ and iozone) and then
>> moving on to pgbench.
>>
>> I'm running FreeBSD and I'm interested in getting some baseline info on
>> UFS2 single disk (SATA 7200/WD RE4), gmirror, zfs mirror, zfs raidz1, zfs
>> set of two mirrors (ie: two mirrored vdevs in a mirror).  Then I'm
>> repeating that with the 4 Intel 320 SSDs, and just to satisfy my
>> curiosity, a zfs mirror with two of the SSDs mirrored as the ZIL.
>>
>> Once that's narrowed down to a few practical choices, I'm moving on to
>> pgbench.  I've found some good info here regarding pgbench that is
>> unfortunately a bit dated:
>> http://www.westnet.com/~gsmith/content/postgresql/
>>
>> A few questions:
>>
>> -Any favorite automation or graphing tools beyond what's on Greg's site?
>
> There are talks not listed on that westnet page - for example a recent
> "Bottom-up Database Benchmarking" talk, available for example here:
>
>   http://pgbr.postgresql.org.br/2011/palestras.php?id=60
>
> It probably contains more recent info about benchmarking tools and testing
> new hardware.
>
>> -Any detailed information on creating "custom" pgbench tests?
>
> The technical info at
> http://www.postgresql.org/docs/9.1/interactive/pgbench.html should be
> sufficient I guess, it's fairly simple. The most difficult thing is
> determining what the script should do - what queries to execute etc. And
> that depends on the application.
>
>> -Any other postgres benchmarking tools?
>
> Not really. The pgbench is a nice stress testing tool and the scripting is
> quite flexible. I've done some TPC-H-like testing recently, but it's
> rather a bunch of scripts executed manually.
>
>> I'm also curious about benchmarking using my own data.  I tried something
>> long ago that at least gave the illusion of working, but didn't seem quite
>> right to me.  I enabled basic query logging on one of our busier servers,
>> dumped the db, and let it run for 24 hours.  That gave me the normal
>> random data from users throughout the day as well as our batch jobs that
>> run overnight.  I had to grep out and reformat the actual queries from the
>> logfile, but that was not difficult.   I then loaded the dump into the
>> test server and basically fed the saved queries into it and timed the
>> result.  I also hacked together a script to sample cpu and disk stats
>> every 2S and had that feeding into an rrd database so I could see how
>> "busy" things were.
>>
>> In theory, this sounded good (to me), but I'm not sure I trust the
>> results.  Any suggestions on the general concept?  Is it sound?  Is there
>> a better way to do it?  I really like the idea of using (our) real data.
>
> It's definitely a step in the right direction. An application-specific
> benchmark is usually much more useful that a generic stress test. It
> simply is going to tell you more about your workload and you can use it to
> asses the capacity more precisely.
>
> There are some issues though - mostly about transactions and locking. For
> example if the client starts a transaction, locks a bunch of records and
> then performs a time-consuming processing task outside the database, the
> other clients may be locked. You won't see this during the stress test,
> because in reality it looks like this
>
> 1) A: BEGIN
> 2) A: LOCK (table, row, ...)
> 3) A: perform something expensive
> 4) B: attempt to LOCK the same resource (blocks)
> 5) A: release the LOCK
> 6) B: obtains the LOCK and continues
>
> but when replaying the workload, you'll see this
>
> 1) A: BEGIN
> 2) A: LOCK (table, row, ...)
> 3) B: attempt to LOCK the same resource (blocks)
> 4) A: release the LOCK
> 5) B: obtains the LOCK and continues
>
> so B waits for a very short period of time (or not at all).
>
> To identify this problem, you'd have to actually behave like the client.
> For example with a web application, you could use apache bench
> (https://httpd.apache.org/docs/2.0/programs/ab.html) or something like
> that.

I like Tsung: http://tsung.erlang-projects.org/
It is very efficient (you can achieve tens or hundreds of thousands
connections per core)
And you can script scenario in xml (there is also a sql proxy to
record session, and pgfouine as an option to build tsung scenario from
its parsed log).

You can add dynamic stuff in the xml (core function provided by tsung)
and also write your own erland modules to add complexity to your
scenario.
--
Cédric Villemain +33 (0)6 20 30 22 52
http://2ndQuadrant.fr/
PostgreSQL: Support 24x7 - Développement, Expertise et Formation