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Wenchen Fan 859a53424a [SPARK-35447][SQL] Optimize skew join before coalescing shuffle partitions 
### What changes were proposed in this pull request?

This PR improves the interaction between partition coalescing and skew handling by moving the skew join rule ahead of the partition coalescing rule and making corresponding changes to the two rules:
1. Simplify `OptimizeSkewedJoin` as it doesn't need to handle `CustomShuffleReaderExec` anymore.
2. Update `CoalesceShufflePartitions` to support coalescing non-skewed partitions.

### Why are the changes needed?

It's a bit hard to reason about skew join if partitions have been coalesced. A skewed partition needs to be much larger than other partitions and we need to look at the raw sizes before coalescing.

It also makes `OptimizeSkewedJoin` more robust, as we don't need to worry about a skewed partition being coalesced with a small partition and breaks skew join handling.

It also helps with https://github.com/apache/spark/pull/31653 , which needs to move `OptimizeSkewedJoin` to an earlier phase and run before `CoalesceShufflePartitions`.

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

new UT and existing tests

Closes #32594 from cloud-fan/shuffle.

Lead-authored-by: Wenchen Fan <wenchen@databricks.com>
Co-authored-by: Wenchen Fan <cloud0fan@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
2021-05-25 13:12:45 +00:00
..
catalyst [SPARK-35455][SQL] Unify empty relation optimization between normal and AQE optimizer 2021-05-25 08:59:59 +00:00
core [SPARK-35447][SQL] Optimize skew join before coalescing shuffle partitions 2021-05-25 13:12:45 +00:00
hive [SPARK-28551][SQL][FOLLOWUP] Use the corrected hadoop conf 2021-05-22 10:33:57 +08:00
hive-thriftserver [SPARK-35286][SQL] Replace SessionState.start with SessionState.setCurrentSessionState 2021-05-16 18:39:15 +08:00
create-docs.sh [SPARK-34010][SQL][DODCS] Use python3 instead of python in SQL documentation build 2021-01-05 19:48:10 +09:00
gen-sql-api-docs.py [SPARK-34747][SQL][DOCS] Add virtual operators to the built-in function document 2021-03-19 10:19:26 +09:00
gen-sql-config-docs.py [SPARK-31550][SQL][DOCS] Set nondeterministic configurations with general meanings in sql configuration doc 2020-04-27 17:08:52 +09:00
gen-sql-functions-docs.py [SPARK-31562][SQL] Update ExpressionDescription for substring, current_date, and current_timestamp 2020-04-26 11:46:52 -07:00
mkdocs.yml [SPARK-30731] Update deprecated Mkdocs option 2020-02-19 17:28:58 +09:00
README.md

README.md

Spark SQL

This module provides support for executing relational queries expressed in either SQL or the DataFrame/Dataset API.

Spark SQL is broken up into four subprojects:

  • Catalyst (sql/catalyst) - An implementation-agnostic framework for manipulating trees of relational operators and expressions.
  • Execution (sql/core) - A query planner / execution engine for translating Catalyst's logical query plans into Spark RDDs. This component also includes a new public interface, SQLContext, that allows users to execute SQL or LINQ statements against existing RDDs and Parquet files.
  • Hive Support (sql/hive) - Includes extensions that allow users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes. There are also wrappers that allow users to run queries that include Hive UDFs, UDAFs, and UDTFs.
  • HiveServer and CLI support (sql/hive-thriftserver) - Includes support for the SQL CLI (bin/spark-sql) and a HiveServer2 (for JDBC/ODBC) compatible server.

Running ./sql/create-docs.sh generates SQL documentation for built-in functions under sql/site, and SQL configuration documentation that gets included as part of configuration.md in the main docs directory.