Custom aggregators and filters in coherence aggregators

Question

Hi
I want get max,min,avg function using custom aggregators for my cache data.
I need to filter the data in the cache(),so I am using Likefilter to filter the data and den I need to apply the custom aggregation on the filtered data.
can anyone send me an example to implement this function...

Answer 1

918079 wrote:
I need to get all the values of min,max,count,avg for lakhs of records for multiple times and set to a value object.
If we use default aggregators,Double Min,DoubleMAx,etc., den every time it will create new instances for each aggregator function gets called.
But, I don't want to create multiple instances of each entry aggregators for each functions.
Instead I want to create custom aggregator , which does all the aggregate functions(min,max,avg,count) within the custom aggregator.Hence I can reduce number of instances.
Please help.The worry about object allocation is not really justified. Let's see what allocates objects during executing a parallel aggregation.
1. You allocate memory when deserializing the aggregator: you can't really do anything about it.
*2. You allocate memory for deserializing the entry if you use entry.getValue(). This deserialized object is cached in the entry during execution so it does not matter if you use a single custom aggregator or a parallel composite aggregator composed of 3 parallel aggregators. You can avoid this by not deserializing, instead you use indexes or POF extraction.*
3. You allocate memory when you extract something out of the entry. This allocation practically does not escape eden, so it is unlikely to cause problems. If you don't deserialize the object, then you likely can't escape this one anyway.
4. You allocate a result object from the entry aggregators. This is one object per node sending an aggregation if you have a custom aggregator, and an array and one additional object (for average). The min and max value is already accounted for at bulletpoint 3.
Do you REALLY care about that one very likely stack-allocated object per node per aggregation? How much allocation do you think Coherence does when receiving messages from other nodes? Rest assured, it is more than one result object per node.
Optimize your aggregation by using POF extraction and indexes, that can give you visible results. But you should not worry about the rest in case we are speaking about this use case.
And if you want to know how to write custom aggregators, then look at the documentation of ParallelAwareAggregator and EntryAggregator, and also read the chapter from the Coherence book:
http://www.packtpub.com/article/working-with-aggregators-in-oracle-coherence-3.5
This chapter also contains an example of writing an average calculating aggregator. You can start from there to implement your own version, but as I mentioned, it won't make a visible difference in allocation for this use case. Optimizing away entry deserialization is what makes a difference.
Best regards,
Robert