We have already discovered the goodness of Jackson for vending out JSON data in a JAX-RS setup. In many cases, our domain objects have references to other domain objects that are not under our control (e.g. classes from third-party JARs). We can easily add annotations to our domain objects to indicate which fields to ignore, but what do we do for the third party objects? One could choose to write custom bean serializers, but that is pretty onerous on the part of the user and one that requires higher maintenance since it is away from the original class. Here is where Jackson Mixins comes to the rescue.
Monday, June 24, 2013
Wednesday, June 12, 2013
Know your disk latency numbers
I was looking around for a tool that will help quantify the latency difference between a NFS-mounted location to a local location and came across ioping. As the documentation indicates, it tries to represent disk latency in pretty much the same way as the ping command shows network latency to a desired host.
I had to build it from source for our linux installation - but the process went about without a hitch. I first tried it on my NFS mounted home drive where the checked-out code, eclipse workspace and maven repository reside and is the hotspot for IO activity when developing. Using a sample invocation from the documentation site, I tried it for a chunk of size 1MB, ten times.
$>ioping -c 10 -s 1M --- /home/kilo(nfs fs1.kilo.com:/vol/home/kilo) ioping statistics --- 10 requests completed in 9101.5 ms, 102 iops, 102.1 mb/s min/avg/max/mdev = 9.5/9.8/10.0/0.2 ms
Next was to test out the performance of our local partition with the same parameters:
--- /local/kilo (ext4 /dev/ssda) ioping statistics --- 10 requests completed in 9052.4 ms, 201 iops, 200.8 mb/s min/avg/max/mdev = 4.8/5.0/5.6/0.2 ms
Result was roughly a speed-up of 200%!
For kicks, I tried it out on a /tmp location as well with the same parameters:
--- /tmp (tmpfs none) ioping statistics --- 10 requests completed in 9004.1 ms, 5219 iops, 5219.2 mb/s min/avg/max/mdev = 0.1/0.2/0.3/0.0 ms
That was roughly 30 times faster - but hold on - what is that tmpfs that is mentioned. Digging further, it seems tmpfs is a special filesystem that doesn't reside on a physical disk but rather stored in the physical memory (albeit volatile) - so the speed-up in access is kind of expected. Which also means that we should be extra nice about what goes in /tmp in such a setup. Keeping a lot of garbage in there and not cleaning up will come and bite us at unpredictable times. Guess many people already know about this
Coming back to the utility itself, there are options to change working set sizes, offsets into files that wish to be seeked, etc. One particularly interesting feature is the option to use write IO, but that option was not available in the 0.6 that I downloaded. An issue indicates that this is a yet to be released feature and will be interesting to see it in action.
I think this will a good utility to have in our linux installations by default. If there are other utilities that do similar stuff but comes out of the box from a stock RHEL installation, please let me know. Hope this helps!
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