[Mondrian] CellBatchSize

Matt Campbell mcampbell at pentaho.com
Thu Jun 27 09:22:39 EDT 2013

There have been reports in the forum over the past few months of cases where performance is much worse in Mondrian 3.5/6 compared to 3.3.  What I think is going on is that some queries significantly exceed the cellBatchSize, causing a whole sequence of segment load queries, each with a different IN list for the items in that particular batch.  The benefits of batching cells in these cases are greatly outweighed by the cost of extra SQL queries.

A couple questions:

1)      I notice that the default value of cellBatchSize is -1, which I would interpret as meaning that there is no hard limit on the number of cells batched together.  In FastBatchingCellReader, though, if cellBatchSize is less than 0 we set the limit at a hardcoded 100000.  Should we provide some way of truly having no hard limit for cellBatchSize?

2)      More generally--what is the benefit of batching, and what can we do to balance that against the cost of extra queries?

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