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Zhenhua Wang 5ecdc7c5c0 [SPARK-18559][SQL] Fix HLL++ with small relative error 
## What changes were proposed in this pull request?

In `HyperLogLogPlusPlus`, if the relative error is so small that p >= 19, it will cause ArrayIndexOutOfBoundsException in `THRESHOLDS(p-4)` . We should check `p` and when p >= 19, regress to the original HLL result and use the small range correction they use.

The pr also fixes the upper bound in the log info in `require()`.
The upper bound is computed by:
```
val relativeSD = 1.106d / Math.pow(Math.E, p * Math.log(2.0d) / 2.0d)
```
which is derived from the equation for computing `p`:
```
val p = 2.0d * Math.log(1.106d / relativeSD) / Math.log(2.0d)
```

## How was this patch tested?

add test cases for:
1. checking validity of parameter relatvieSD
2. estimation with smaller relative error so that p >= 19

Author: Zhenhua Wang <wzh_zju@163.com>
Author: wangzhenhua <wangzhenhua@huawei.com>

Closes #15990 from wzhfy/hllppRsd.
2016-11-25 05:02:48 -08:00
..
catalyst [SPARK-18559][SQL] Fix HLL++ with small relative error 2016-11-25 05:02:48 -08:00
core [SPARK-3359][BUILD][DOCS] More changes to resolve javadoc 8 errors that will help unidoc/genjavadoc compatibility 2016-11-25 11:27:07 +00:00
hive [SPARK-3359][BUILD][DOCS] More changes to resolve javadoc 8 errors that will help unidoc/genjavadoc compatibility 2016-11-25 11:27:07 +00:00
hive-thriftserver [SPARK-14914][CORE] Fix Resource not closed after using, for unit tests and example 2016-11-10 10:54:36 +00:00
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.