Luca Canali created SPARK-21519:
-----------------------------------
Summary: Add an option to the JDBC data source to initialize the
environment of the remote database session
Key: SPARK-21519
URL: https://issues.apache.org/jira/browse/SPARK-21519
Project: Spark
Issue Type: New Feature
Components: SQL
Affects Versions: 2.2.0, 2.1.1, 2.1.0
Reporter: Luca Canali
Priority: Minor
This proposes an option to the JDBC datasource, tentatively called "
sessionInitStatement" to implement the functionality of session initialization
present for example in the Sqoop connector for Oracle (see
https://sqoop.apache.org/docs/1.4.6/SqoopUserGuide.html#_oraoop_oracle_session_initialization_statements
) . After each database session is opened to the remote DB, and before
starting to read data, this option executes a custom SQL statement (or a PL/SQL
block in the case of Oracle).
Example of usage, relevant to Oracle JDBC:
```
val preambleSQL="""
begin
execute immediate 'alter session set tracefile_identifier=sparkora';
execute immediate 'alter session set "_serial_direct_read"=true';
execute immediate 'alter session set time_zone=''+02:00''';
end;
bin/spark-shell –jars ojdb6.jar
val df = spark.read.format("jdbc").option("url",
"jdbc:oracle:thin:@ORACLEDBSERVER:1521/service_name").option("driver",
"oracle.jdbc.driver.OracleDriver").option("dbtable", "(select 1, sysdate,
systimestamp, current_timestamp, localtimestamp from dual)").option("user",
"MYUSER").option("password",
"MYPASSWORK").option("fetchsize",1000).option("sessionInitStatement",
preambleSQL).load()
df.show(5,false)
```
Comments: This proposal has been developed and tested for connecting the Spark
JDBC data source to Oracle databases, however it believe it can be useful for
other target DBs too, as it is quite generic.
Note the proposed code allows to inject SQL into the target database. This is
not a security concern as such, as it requires password authentication, however
beware of the possibilities for injecting user-provided SQL (and PL/SQL) that
this opens.
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