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doc: Add memory tuning section to user guide #684

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doc: Add memory tuning section to user guide
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Update docs/source/user-guide/tuning.md
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15 changes: 15 additions & 0 deletions docs/source/user-guide/tuning.md
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Expand Up @@ -21,6 +21,21 @@ under the License.

Comet provides some tuning options to help you get the best performance from your queries.

## Memory Tuning

Comet currently doesn't share the memory allocation from Spark but owns its own memory allocation.
That's said, Comet requires additional memory to be allocated. Comet provides some memory related configurations to help you tune the memory usage.

By default, the amount of memory is `spark.comet.memory.overhead.factor` * `spark.executor.memory`.
The default value for `spark.comet.memory.overhead.factor` is 0.2. You can increase the factor to require more
memory for Comet to use, if you see OOM error. Generally, increasing memory overhead will improve the performance of your queries.
For example, some operators like `SortMergeJoin` and `HashAggregate` may require more memory to run.
Once the memory is not enough, the operator will spill to disk, which will slow down the query.

Besides, you can also set the memory explicitly by setting `spark.comet.memoryOverhead` to the desired value.
Comet will allocate at least `spark.comet.memory.overhead.min` memory.

If both `spark.comet.memoryOverhead` and `spark.comet.memory.overhead.factor` are set, the former will be used.

## Shuffle

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