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Zhenhua Wang 9d0db5a7f8 [SPARK-20881][SQL] Clearly document the mechanism to choose between two sources of statistics 
## What changes were proposed in this pull request?

Now, we have two sources of statistics, i.e. Spark's stats and Hive's stats. Spark's stats is generated by running "analyze" command in Spark. Once it's available, we respect this stats over Hive's.

This pr is to clearly document in related code the mechanism to choose between these two sources of stats.

## How was this patch tested?

Not related.

Author: Zhenhua Wang <wzh_zju@163.com>

Closes #18105 from wzhfy/cboSwitchStats.
2017-05-28 13:32:45 -07:00
..
catalyst [SPARK-20841][SQL] Support table column aliases in FROM clause 2017-05-28 13:23:18 -07:00
core [SPARK-20841][SQL] Support table column aliases in FROM clause 2017-05-28 13:23:18 -07:00
hive [SPARK-20881][SQL] Clearly document the mechanism to choose between two sources of statistics 2017-05-28 13:32:45 -07:00
hive-thriftserver [SPARK-20393][WEBU UI] Strengthen Spark to prevent XSS vulnerabilities 2017-05-10 10:59:57 +01:00
README.md [SPARK-16557][SQL] Remove stale doc in sql/README.md 2016-07-14 19:24:42 -07:00

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 an extension of SQLContext called HiveContext that allows users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes. There are also wrappers that allows 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.