cc1d2dcb61
## What changes were proposed in this pull request?
This PR adds a boolean option, `truncate`, for `SaveMode.Overwrite` of JDBC DataFrameWriter. If this option is `true`, it try to take advantage of `TRUNCATE TABLE` instead of `DROP TABLE`. This is a trivial option, but will provide great **convenience** for BI tool users based on RDBMS tables generated by Spark.
**Goal**
- Without `CREATE/DROP` privilege, we can save dataframe to database. Sometime these are not allowed for security.
- It will preserve the existing table information, so users can add and keep some additional `INDEX` and `CONSTRAINT`s for the table.
- Sometime, `TRUNCATE` is faster than the combination of `DROP/CREATE`.
**Supported DBMS**
The following is `truncate`-option support table. Due to the different behavior of `TRUNCATE TABLE` among DBMSs, it's not always safe to use `TRUNCATE TABLE`. Spark will ignore the `truncate` option for **unknown** and **some** DBMS with **default CASCADING** behavior. Newly added JDBCDialect should implement corresponding function to support `truncate` option additionally.
Spark Dialects | `truncate` OPTION SUPPORT
---------------|-------------------------------
MySQLDialect | O
PostgresDialect | X
DB2Dialect | O
MsSqlServerDialect | O
DerbyDialect | O
OracleDialect | O
**Before (TABLE with INDEX case)**: SparkShell & MySQL CLI are interleaved intentionally.
```scala
scala> val (url, prop)=("jdbc:mysql://localhost:3306/temp?useSSL=false", new java.util.Properties)
scala> prop.setProperty("user","root")
scala> df.write.mode("overwrite").jdbc(url, "table_with_index", prop)
scala> spark.range(10).write.mode("overwrite").jdbc(url, "table_with_index", prop)
mysql> DESC table_with_index;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id | bigint(20) | NO | | NULL | |
+-------+------------+------+-----+---------+-------+
mysql> CREATE UNIQUE INDEX idx_id ON table_with_index(id);
mysql> DESC table_with_index;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id | bigint(20) | NO | PRI | NULL | |
+-------+------------+------+-----+---------+-------+
scala> spark.range(10).write.mode("overwrite").jdbc(url, "table_with_index", prop)
mysql> DESC table_with_index;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id | bigint(20) | NO | | NULL | |
+-------+------------+------+-----+---------+-------+
```
**After (TABLE with INDEX case)**
```scala
scala> spark.range(10).write.mode("overwrite").option("truncate", true).jdbc(url, "table_with_index", prop)
mysql> DESC table_with_index;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id | bigint(20) | NO | PRI | NULL | |
+-------+------------+------+-----+---------+-------+
```
**Error Handling**
- In case of exceptions, Spark will not retry. Users should turn off the `truncate` option.
- In case of schema change:
- If one of the column names changes, this will raise exceptions intuitively.
- If there exists only type difference, this will work like Append mode.
## How was this patch tested?
Pass the Jenkins tests with a updated testcase.
Author: Dongjoon Hyun <dongjoon@apache.org>
Closes #14086 from dongjoon-hyun/SPARK-16410.
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Apache Spark
Spark is a fast and general cluster computing system for Big Data. It provides high-level APIs in Scala, Java, Python, and R, and an optimized engine that supports general computation graphs for data analysis. It also supports a rich set of higher-level tools including Spark SQL for SQL and DataFrames, MLlib for machine learning, GraphX for graph processing, and Spark Streaming for stream processing.
Online Documentation
You can find the latest Spark documentation, including a programming guide, on the project web page and project wiki. This README file only contains basic setup instructions.
Building Spark
Spark is built using Apache Maven. To build Spark and its example programs, run:
build/mvn -DskipTests clean package
(You do not need to do this if you downloaded a pre-built package.)
You can build Spark using more than one thread by using the -T option with Maven, see "Parallel builds in Maven 3". More detailed documentation is available from the project site, at "Building Spark". For developing Spark using an IDE, see Eclipse and IntelliJ.
Interactive Scala Shell
The easiest way to start using Spark is through the Scala shell:
./bin/spark-shell
Try the following command, which should return 1000:
scala> sc.parallelize(1 to 1000).count()
Interactive Python Shell
Alternatively, if you prefer Python, you can use the Python shell:
./bin/pyspark
And run the following command, which should also return 1000:
>>> sc.parallelize(range(1000)).count()
Example Programs
Spark also comes with several sample programs in the examples directory.
To run one of them, use ./bin/run-example <class> [params]. For example:
./bin/run-example SparkPi
will run the Pi example locally.
You can set the MASTER environment variable when running examples to submit
examples to a cluster. This can be a mesos:// or spark:// URL,
"yarn" to run on YARN, and "local" to run
locally with one thread, or "local[N]" to run locally with N threads. You
can also use an abbreviated class name if the class is in the examples
package. For instance:
MASTER=spark://host:7077 ./bin/run-example SparkPi
Many of the example programs print usage help if no params are given.
Running Tests
Testing first requires building Spark. Once Spark is built, tests can be run using:
./dev/run-tests
Please see the guidance on how to run tests for a module, or individual tests.
A Note About Hadoop Versions
Spark uses the Hadoop core library to talk to HDFS and other Hadoop-supported storage systems. Because the protocols have changed in different versions of Hadoop, you must build Spark against the same version that your cluster runs.
Please refer to the build documentation at "Specifying the Hadoop Version" for detailed guidance on building for a particular distribution of Hadoop, including building for particular Hive and Hive Thriftserver distributions.
Configuration
Please refer to the Configuration Guide in the online documentation for an overview on how to configure Spark.