[infinispan-dev] CHM or CHMv8?

[Sanne Grinovero]

On 19 April 2013 11:10, Dan Berindei <dan.berindei at gmail.com> wrote:
>
>
>
> On Fri, Apr 19, 2013 at 12:58 PM, Sanne Grinovero <sanne at infinispan.org>
> wrote:
>>
>> On 19 April 2013 10:37, Dan Berindei <dan.berindei at gmail.com> wrote:
>> > Testing mixed read/write performance with capacity 100000, keys 300000,
>> > concurrency level 32, threads 12, read:write ratio 99:1
>> > Container CHM           Ops/s 5178894.77  Gets/s 5127105.82  Puts/s
>> > 51788.95  HitRatio      86.23  Size     177848  stdDev   60896.42
>> > Container CHMV8         Ops/s 5768824.37  Gets/s 5711136.13  Puts/s
>> > 57688.24  HitRatio      84.72  Size     171964  stdDev   60249.99
>>
>> Nice, thanks.
>> >
>> > The test is probably limited by the 1% writes, but I think it does show
>> > that
>> > reads in CHMV8 are not slower than reads in OpenJDK7's CHM.
>> > I haven't measured it, but the memory footprint should also be better,
>> > because it doesn't use segments any more.
>> >
>> > AFAIK the memoryCHMV8 also uses copy-on-write at the bucket level, but
>> > we
>> > could definitely do a pure read test with a HashMap to see how big the
>> > performance difference is.
>>
>> By copy-on-write I didn't mean on the single elements, but on the
>> whole map instance:
>>
>> private volatile HashMap configuration;
>>
>> synchronized addConfigurationProperty(String, String) {
>>      HashMap newcopy = new HashMap( configuration ):
>>      newcopy.put(..);
>>      configuration = newcopy;
>> }
>>
>> Of course that is never going to scale for writes, but if writes stop
>> at runtime after all services are started I would expect that the
>> simplicity of the non-threadsafe HashMap should have some benefit over
>> CHM{whatever}, or it would have been removed already?
>>
>
> Right, we should be able to tell whether that's worth doing with a pure read
> test with a CHMV8 and a HashMap :)

IFF you find out CHMV8 is as good as HashMap for read only, you have
two options:
 - ask the JDK team to drop the HashMap code as it's no longer needed
 - fix your benchmark :-P

In other words, I'd consider it highly surprising and suspicious
(still interesting though!)

Cheers,
Sanne