multiple pools in Java

[Greg Whalin]

I threw in support for multiple pools tonight as well as added in a few 
additional bug fixes and improvements to other parts of the code (a 
keyExists() method, better unit tests, bug fix to getCounter(), and some 
general code cleanup).  This is not as tested as I would like it to be, 
so I don't plan on releasing this yet.  However, feel free to grab head 
release from subversion repository ( see 
http://www.whalin.com/memcached/#source for instructions ).  Let me know 
if this helps.

Greg

Mybrid Spalding wrote:
> Hi!
>    Absolutely awesome stuff and its wonderful that you reply. We really 
> appreciate it. Sorry if I'm a bit drippy here but its good I think to 
> over acknowledge.
>    This is really good stuff and we'll put your advice about 
> serialization in our work que.    However, if you do take the time to 
> add multiple pools this would be much simpler for us to do since it 
> would just involve a size test  to determine which pool.
>   
>    Again, thanks so much.
> 
> 
> Sincerely,
> -Mybrid
> 
> Greg Whalin wrote:
> 
>> I responded to you directly, but will update to the list.  We saw 
>> similar behavior simply due to the objects we were caching.  Most of 
>> our objects were fairly small in size, but the occassional object 
>> would be much much larger (10-15 times larger than our average).  
>> These objects would show up to be cached at random points, and 
>> generally well after the memcached server had "settled in".  We would 
>> get out of memory errors.
>>
>> We dealt with this problem in two ways.  One, we stopped relying on 
>> default java serialization.  While the default serialization works 
>> great, it is far from being efficient if you care about size of the 
>> serialized object.  Instead, we use java.io.Externalizable and we 
>> implemented our own serialization scheme.  Instant 60% savings in size 
>> of objects.
>>
>> Second, we turned on gzip compression in the client.  Now, my tests 
>> and benchmarks show that java gzip compression is slow ... horribly 
>> slow, so we really wanted to avoid using it wide scale.  We set our 
>> compression threshold so that we only compressed objects > 128K.  This 
>> combination of things solved all of our problems.  We have yet to see 
>> another out of memory error from memcached in 8 months of heavy usage.
>>
>> Now, as to multiple pools.  Currently, the java memcache client pool 
>> is a singleton, so it is not possible to create multiple pools.  I 
>> think I could modify the code to allow for multiple pools pretty 
>> easily, but I would need to go through everything to make sure all 
>> code would continue to work correctly.  If I get some time, I will 
>> look into this approach over the weekend.
>>
>> Greg
>>
>> Mybrid Spalding wrote:
>>
>>> Hi!
>>>  Happy Thursday! Thanks so much for replying.
>>>  Ok, here is more detail. We  are having excellent success with this 
>>> very well designed product. One problem we are having is that large 
>>> objects only have a cache hit rate of 45% while small objects are 90% 
>>> plus. We speculate the root cause is that our web site uses objects 
>>> of every size imaginable and that there is not enough slab space for 
>>> large sized objects.  We'd like to experiment with segmenting by 
>>> writing objects larger than X to one cache pool where we tune X.
>>>  Any thoughts on this would be greatly appreciated. JFYI, your cache 
>>> has helped us nearly double our bandwidth and we really truly 
>>> appreciate this product.
>>>
>>> Thanks!
>>> -Mybrid
>>>
>>>
>>>  
>>> Thanks!
>>> -Mybrid
>>>
>>> Brad Fitzpatrick wrote:
>>>
>>>> Why don't you just make one pool that's twice as big, then?
>>>>
>>>> If a node in a pool dies, the memcached client just routes around it 
>>>> and
>>>> spreads the load to the nodes that are still alive.
>>>>
>>>>
>>>> On Tue, 5 Apr 2005, Mybrid Spalding wrote:
>>>>
>>>>  
>>>>
>>>>> Hi!
>>>>>  Greetings from a first-time poster. I'm currently using the Java
>>>>> client to connect to memcached. For robustness reasons I'm thinking of
>>>>> segementing traffic to different caches. That way if one cache pool 
>>>>> goes
>>>>> down I can route to another. However, reading the Java docs its not
>>>>> obvious to me how to or a good strategy.
>>>>>
>>>>>
>>>>> Thanks!
>>>>> -Mybrid
>>>>>
>>>>>
>>>>>   
>>>>
>>>>
>>>>
>>>>  
>>>>
>>>
>>
> 
> -- 
> Mybrid Spalding
> CTO-DataRebels, Inc.
> 1920 Rock Street #2
> Mountain View, CA  94043
> Office: (650) 965-4217
> Mobile: (650) 450-1636
> www.datarebels.com
>