# Validate the Migration

In addition to the monitoring user interface provided by Spark, you can run another program, after running a migration, to check whether the destination table contains exactly the same items as the source table.

Running this program consists of submitting the same Spark job as the migration, but with a different entry point.

Before running the validator, adjust the corresponding configuration in the top-level `validation` property of the file `config.yml`:

```yaml
validation:
  # Should WRITETIMEs and TTLs be compared?
  compareTimestamps: true
  # What difference should we allow between TTLs?
  ttlToleranceMillis: 60000
  # What difference should we allow between WRITETIMEs?
  writetimeToleranceMillis: 1000
  # How many differences to fetch and print
  failuresToFetch: 100
  # What difference should we allow between floating point numbers?
  floatingPointTolerance: 0.001
  # What difference in ms should we allow between timestamps?
  timestampMsTolerance: 0
```

The exact way to run the validator depends on the way you set up the Spark cluster.

## Run the Validator in the Ansible-based Setup

Submit the job `submit-cql-job-validator.sh`.

## Run the Validator in a Manual Spark Setup

Pass the argument `--class com.scylladb.migrator.Validator` to the `spark-submit` invocation:

```bash
spark-submit --class com.scylladb.migrator.Validator \
  --master spark://<spark-master-hostname>:7077 \
  --conf spark.scylla.config=<path to config.yaml> \
  <path to scylla-migrator-assembly.jar>
```

## Run the Validator in AWS EMR

Use the following arguments for the Cluster Step that runs a custom JAR:

```text
spark-submit --deploy-mode cluster --class com.scylladb.migrator.Validator --conf spark.scylla.config=/mnt1/config.yaml /mnt1/scylla-migrator-assembly.jar
```

## Run the Validator in a Docker-based Spark Setup

Pass the argument `--class com.scylladb.migrator.Validator` to the `spark-submit` invocation:

```bash
docker compose exec spark-master /spark/bin/spark-submit --class com.scylladb.migrator.Validator \
  --master spark://spark-master:7077 \
  --conf spark.driver.host=spark-master \
  --conf spark.scylla.config=/app/config.yaml \
  /jars/scylla-migrator-assembly.jar
```