parthchandra commented on code in PR #345: URL: https://github.com/apache/datafusion-comet/pull/345#discussion_r1586638726
########## docs/source/contributor-guide/plugin_overview.md: ########## @@ -0,0 +1,50 @@ +<!-- +Licensed to the Apache Software Foundation (ASF) under one +or more contributor license agreements. See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you under the Apache License, Version 2.0 (the +"License"); you may not use this file except in compliance +with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, +software distributed under the License is distributed on an +"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +KIND, either express or implied. See the License for the +specific language governing permissions and limitations +under the License. +--> + +# Comet Plugin Overview + +The entry point to Comet is the `org.apache.comet.CometSparkSessionExtensions` class, which can be registered with Spark by adding the following setting to the Spark configuration when launching `spark-shell` or `spark-submit`: + +``` +--conf spark.sql.extensions=org.apache.comet.CometSparkSessionExtensions +``` + +On initialization, this class registers two physical plan optimization rules with Spark: `CometScanRule` and `CometExecRule`. These rules run whenever a query stage is being planned. + +## CometScanRule + +`CometScanRule` replaces any Parquet scans with Comet Parquet scan classes. + +When the V1 data source API is being used, `FileSourceScanExec` is replaced with `CometScanExec`. + +When the V2 data source API is being used, `BatchScanExec` is replaced with `CometBatchScanExec`. + +## CometExecRule + +`CometExecRule` attempts to transform a Spark physical plan into a Comet plan. + +This rule traverses bottom-up from the original Spark plan and attempts to replace each node with a Comet equivalent. For example, a `ProjectExec` will be replaced by `CometProjectExec`. + +When replacing a node, various checks are performed to determine if Comet can support the operator and its expressions. If an operator or expression is not supported by Comet then the reason will be stored in a tag on the underlying Spark node. Running `explain` on a query will show any reasons that prevented the plan from being executed natively in Comet. If any part of the plan is not supported in Comet then the original Spark plan will be returned. Review Comment: Sorry, just seeing this today. The `explain` information will show up in the UI or `EXPLAIN` output only from Spark 4.0.0 onwards as the `ExtendedExplainGenerator` trait was only added in Spark 4.0. Internally, we can always call `ExtendedExplainInfo.generateExtendedInfo(plan)` -- 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
