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Friday, September 26, 2014

DataStage Warning - Agg,1: Hash table has grown to 16384 entries

Sometime when we are running Datastage job in which we are using Aggregator stage, we get below warning -

Agg,1: Hash table has grown to 16384 entries.
Agg,0: Hash table has grown to 16384 entries. 

Solution :

Go to Aggregator stage properties.                                      
In the options property of the Aggregator stage select Method=Sort not Hash. As Hash table aggregation method is recommended for 1000 or fewer distinct grouping values per MB.

Note : -
As stated in the Parallel Job Developer Guide, Aggregator's hash method is typically used for a relatively small number of groups (distinct key values). The more groups in your data, the more memory will be used by the operator as it builds it's hash table of group values and calculations. 

Hash method allows you to not need to sort your data prior to entering the Aggregator (although you should still partition it). For a large number of groups, pre-sorting the data and using the Sort method in Aggregator may likely be more efficient.

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