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[[validation]]
+validation+
--------------


Purpose
~~~~~~~

Validate the data copied, either import or export by comparing the row
counts from the source and the target post copy.


Introduction
~~~~~~~~~~~~

There are 3 basic interfaces:
ValidationThreshold - Determines if the error margin between the source and
target are acceptable: Absolute, Percentage Tolerant, etc.
Default implementation is AbsoluteValidationThreshold which ensures the row
counts from source and targets are the same.

ValidationFailureHandler - Responsible for handling failures: log an
error/warning, abort, etc.
Default implementation is LogOnFailureHandler that logs a warning message to
the configured logger.

Validator - Drives the validation logic by delegating the decision to
ValidationThreshold and delegating failure handling to ValidationFailureHandler.
The default implementation is RowCountValidator which validates the row
counts from source and the target.


Syntax
~~~~~~

----
$ sqoop import (generic-args) (import-args)
$ sqoop export (generic-args) (export-args)
----

Validation arguments are part of import and export arguments.


Configuration
~~~~~~~~~~~~~

The validation framework is extensible and pluggable. It comes with default
implementations but the interfaces can be extended to allow custom
implementations by passing them as part of the command line arguments as
described below.


.Validator
 Property:         validator
 Description:      Driver for validation,
                   must implement org.apache.sqoop.validation.Validator
 Supported values: The value has to be a fully qualified class name.
 Default value:    org.apache.sqoop.validation.RowCountValidator

.Validation Threshold
 Property:         validation-threshold
 Description:      Drives the decision based on the validation meeting the
                   threshold or not. Must implement
                   org.apache.sqoop.validation.ValidationThreshold
 Supported values: The value has to be a fully qualified class name.
 Default value:    org.apache.sqoop.validation.AbsoluteValidationThreshold

.Validation Failure Handler
 Property:         validation-failurehandler
 Description:      Responsible for handling failures, must implement
                   org.apache.sqoop.validation.ValidationFailureHandler
 Supported values: The value has to be a fully qualified class name.
 Default value:    org.apache.sqoop.validation.AbortOnFailureHandler


Limitations
~~~~~~~~~~~

Validation currently only validates data copied from a single table into HDFS.
The following are the limitations in the current implementation:

* all-tables option
* free-form query option
* Data imported into Hive, HBase or Accumulo
* table import with --where argument
* incremental imports


Example Invocations
~~~~~~~~~~~~~~~~~~~

A basic import of a table named +EMPLOYEES+ in the +corp+ database that uses
validation to validate the row counts:

----
$ sqoop import --connect jdbc:mysql://db.foo.com/corp  \
    --table EMPLOYEES --validate
----

A basic export to populate a table named +bar+ with validation enabled:

----
$ sqoop export --connect jdbc:mysql://db.example.com/foo --table bar  \
    --export-dir /results/bar_data --validate
----

Another example that overrides the validation args:

----
$ sqoop import --connect jdbc:mysql://db.foo.com/corp --table EMPLOYEES \
    --validate --validator org.apache.sqoop.validation.RowCountValidator \
    --validation-threshold \
          org.apache.sqoop.validation.AbsoluteValidationThreshold \
    --validation-failurehandler \
          org.apache.sqoop.validation.AbortOnFailureHandler
----