andygrove commented on code in PR #1525: URL: https://github.com/apache/datafusion-comet/pull/1525#discussion_r2003524352
########## docs/source/user-guide/tuning.md: ########## @@ -17,18 +17,96 @@ specific language governing permissions and limitations under the License. --> -# Tuning Guide +# Comet Tuning Guide Comet provides some tuning options to help you get the best performance from your queries. ## Memory Tuning -### Unified Memory Management with Off-Heap Memory +It is necessary to specify how much memory Comet can use in addition to memory already allocated to Spark. In some +cases, it may be possible to reduce the amount of memory allocated to Spark so that overall memory allocation is +the same or lower than the original configuration. In other cases, enabling Comet may require allocating more memory +than before. See the [Determining How Much Memory to Allocate] section for more details. -The recommended way to share memory between Spark and Comet is to set `spark.memory.offHeap.enabled=true`. This allows -Comet to share an off-heap memory pool with Spark. The size of the pool is specified by `spark.memory.offHeap.size`. For more details about Spark off-heap memory mode, please refer to Spark documentation: https://spark.apache.org/docs/latest/configuration.html. +[Determining How Much Memory to Allocate]: #determining-how-much-memory-to-allocate -The type of pool can be specified with `spark.comet.exec.memoryPool`. +Comet supports Spark's on-heap (the default) and off-heap mode for allocating memory. However, we strongly recommend +using off-heap mode. Comet has some limitations when running in on-heap mode, such as requiring more memory overall, +and requiring shuffle memory to be separately configured. + +### Configuring Comet Memory in Off-Heap Mode + +The recommended way to allocate memory for Comet is to set `spark.memory.offHeap.enabled=true`. This allows +Comet to share an off-heap memory pool with Spark, reducing the overall memory overhead. The size of the pool is +specified by `spark.memory.offHeap.size`. For more details about Spark off-heap memory mode, please refer to +Spark documentation: https://spark.apache.org/docs/latest/configuration.html. Review Comment: In `CometDriverPlugin`, we only reference this config if `shouldOverrideMemoryConf` returns `true`. The logic in that method is `cometEnabled && (cometExecShuffle || cometExec) && !unifiedMemory`. `unifiedMemory` here really means `spark.memory.offHeap.enabled`. The intent is not to use this config when running off-heap, because we define the overhead using `spark.memory.offHeap.size` when running in off-heap mode, although there may be places where we are not consistent. I will file an issue to check that we are using this consistently and have adequate tests. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For additional commands, e-mail: github-h...@datafusion.apache.org
