Alex Behm ecdd5688b9 Nested Types: Tuple pointers are owned by the containing RowBatch by default. ...

This patch makes the ownership of the memory backing the tuple pointers of
a RowBatch dependent on whether the legacy joins and aggs are enabled:

By default, the memory is malloc'd and owned by the RowBatch:
If enable_partitioned_hash_join=true and enable_partitioned_aggregation=true
then the memory is owned by the RowBatch and is freed upon its destruction.
This mode is more performant especially with SubplanNodes in the ExecNode tree
because the tuple pointers are not transferred and do not have to be re-created
in every Reset().

Memory is allocated from MemPool:
Otherwise, the memory is allocated from the RowBatch's tuple pool. As a result,
the pointer memory is transferred just like tuple data, and must be re-created
in Reset(). This mode is required for the legacy join and agg which rely on the
tuple pointers being allocated from the RowBatch's tuple pool, so they can
acquire ownership of the tuple pointers.

Performance impact for nested types:
Initial cluster runs and profiling on nested TPCH identified excessive
malloc/frees as a major performance bottleneck. This change paves the way
for further optimizations which yielded a 2x improvement in response time
for most nested TPCH queries.

Change-Id: I4ac58b18058ce46b4db89fbe117b0bcad19e9ee7
Reviewed-on: http://gerrit.cloudera.org:8080/807
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: Internal Jenkins

2015-09-14 13:43:01 -07:00

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