cassandra-data-migrator

Migrate and Validate Tables between Origin and Target Cassandra Clusters.

⚠️ Please note this job has been tested with spark version 3.5.1

Install as a Container

• Get the latest image that includes all dependencies from DockerHub
  • All migration tools (cassandra-data-migrator + dsbulk + cqlsh) would be available in the /assets/ folder of the container

Install as a JAR file

• Download the latest jar file from the GitHub packages area here

Prerequisite

• Install Java11 (minimum) as Spark binaries are compiled with it.
• Install Spark version 3.5.1 on a single VM (no cluster necessary) where you want to run this job. Spark can be installed by running the following: -

wget https://archive.apache.org/dist/spark/spark-3.5.1/spark-3.5.1-bin-hadoop3-scala2.13.tgz
tar -xvzf spark-3.5.1-bin-hadoop3-scala2.13.tgz

⚠️ If the above Spark and Scala version is not properly installed, you'll then see a similar exception like below when running the CDM jobs,

Exception in thread "main" java.lang.NoSuchMethodError: scala.runtime.Statics.releaseFence()V

Steps for Data-Migration:

⚠️ Note that Version 4 of the tool is not backward-compatible with .properties files created in previous versions, and that package names have changed.

1. cdm.properties file needs to be configured as applicable for the environment. Parameter descriptions and defaults are described in the file. The file can have any name, it does not need to be cdm.properties.

   • A simplified sample properties file configuration can be found here as cdm.properties
   • A complete sample properties file configuration can be found here as cdm-detailed.properties

2. Place the properties file where it can be accessed while running the job via spark-submit.
3. Run the below job using spark-submit command as shown below:

./spark-submit --properties-file cdm.properties \
--conf spark.cdm.schema.origin.keyspaceTable="<keyspacename>.<tablename>" \
--master "local[*]" --driver-memory 25G --executor-memory 25G \
--class com.datastax.cdm.job.Migrate cassandra-data-migrator-4.x.x.jar &> logfile_name_$(date +%Y%m%d_%H_%M).txt

Note:

• Above command generates a log file logfile_name_*.txt to avoid log output on the console.
• Update the memory options (driver & executor memory) based on your use-case

Steps for Data-Validation:

• To run the job in Data validation mode, use class option --class com.datastax.cdm.job.DiffData as shown below

./spark-submit --properties-file cdm.properties \
--conf spark.cdm.schema.origin.keyspaceTable="<keyspacename>.<tablename>" \
--master "local[*]" --driver-memory 25G --executor-memory 25G \
--class com.datastax.cdm.job.DiffData cassandra-data-migrator-4.x.x.jar &> logfile_name_$(date +%Y%m%d_%H_%M).txt

• Validation job will report differences as “ERRORS” in the log file as shown below

23/04/06 08:43:06 ERROR DiffJobSession: Mismatch row found for key: [key3] Mismatch: Target Index: 1 Origin: valueC Target: value999) 
23/04/06 08:43:06 ERROR DiffJobSession: Corrected mismatch row in target: [key3]
23/04/06 08:43:06 ERROR DiffJobSession: Missing target row found for key: [key2]
23/04/06 08:43:06 ERROR DiffJobSession: Inserted missing row in target: [key2]

• Please grep for all ERROR from the output log files to get the list of missing and mismatched records.
  • Note that it lists differences by primary-key values.
• The Validation job can also be run in an AutoCorrect mode. This mode can
  • Add any missing records from origin to target
  • Update any mismatched records between origin and target (makes target same as origin).
• Enable/disable this feature using one or both of the below setting in the config file

spark.cdm.autocorrect.missing                     false|true
spark.cdm.autocorrect.mismatch                    false|true

Note:

• The validation job will never delete records from target i.e. it only adds or updates data on target

Migrating or Validating specific partition ranges

• You can also use the tool to Migrate or Validate specific partition ranges by using a partition-file with the name ./<keyspacename>.<tablename>_partitions.csv in the below format in the current folder as input

-507900353496146534,-107285462027022883
-506781526266485690,1506166634797362039
2637884402540451982,4638499294009575633
798869613692279889,8699484505161403540

Each line above represents a partition-range (min,max). Alternatively, you can also pass the partition-file via command-line param as shown below

./spark-submit --properties-file cdm.properties \
 --conf spark.cdm.schema.origin.keyspaceTable="<keyspacename>.<tablename>" \
 --conf spark.cdm.tokenRange.partitionFile="/<path-to-file>/<csv-input-filename>" \
 --master "local[*]" --driver-memory 25G --executor-memory 25G \
 --class com.datastax.cdm.job.<Migrate|DiffData> cassandra-data-migrator-4.x.x.jar &> logfile_name_$(date +%Y%m%d_%H_%M).txt

This mode is specifically useful to processes a subset of partition-ranges that may have failed during a previous run.

Note: A file named ./<keyspacename>.<tablename>_partitions.csv is auto generated by the Migration & Validation jobs in the above format containing any failed partition ranges. No file is created if there are no failed partitions. You can use this file as an input to process any failed partition in a following run.

Perform large-field Guardrail violation checks

• The tool can be used to identify large fields from a table that may break you cluster guardrails (e.g. AstraDB has a 10MB limit for a single large field) --class com.datastax.cdm.job.GuardrailCheck as shown below

./spark-submit --properties-file cdm.properties \
--conf spark.cdm.schema.origin.keyspaceTable="<keyspacename>.<tablename>" \
--conf spark.cdm.feature.guardrail.colSizeInKB=10000 \
--master "local[*]" --driver-memory 25G --executor-memory 25G \
--class com.datastax.cdm.job.GuardrailCheck cassandra-data-migrator-4.x.x.jar &> logfile_name_$(date +%Y%m%d_%H_%M).txt

Features

• Auto-detects table schema (column names, types, keys, collections, UDTs, etc.)
  • Including counter table Counter tables
• Preserve writetimes and TTLs
• Supports migration/validation of advanced DataTypes (Sets, Lists, Maps, UDTs)
• Filter records from Origin using writetimes and/or CQL conditions and/or a list of token-ranges
• Perform guardrail checks (identify large fields)
• Supports adding constants as new columns on Target
• Supports expanding Map columns on Origin into multiple records on Target
• Fully containerized (Docker and K8s friendly)
• SSL Support (including custom cipher algorithms)
• Migrate from any Cassandra Origin (Apache Cassandra® / DataStax Enterprise™ / DataStax Astra DB™) to any Cassandra Target (Apache Cassandra® / DataStax Enterprise™ / DataStax Astra DB™)
• Supports migration/validation from and to Azure Cosmos Cassandra
• Validate migration accuracy and performance using a smaller randomized data-set
• Supports adding custom fixed writetime
• Validation - Log partitions range level exceptions, use the exceptions file as input for rerun

Known Limitations

• This tool does not migrate ttl & writetime at the field-level (for optimization reasons). It instead finds the field with the highest ttl & the field with the highest writetime within an origin row and uses those values on the entire target row.

Building Jar for local development

1. Clone this repo
2. Move to the repo folder cd cassandra-data-migrator
3. Run the build mvn clean package (Needs Maven 3.9.x)
4. The fat jar (cassandra-data-migrator-4.x.x.jar) file should now be present in the target folder

Contributors

Checkout all our wonderful contributors here.

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