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Efficiently diff data in or across relational databases

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Datafold

data-diff: Compare datasets fast, within or across SQL databases

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Use Cases

Data Migration & Replication Testing

Compare source to target and check for discrepancies when moving data between systems:

  • Migrating to a new data warehouse (e.g., Oracle > Snowflake)
  • Converting SQL to a new transformation framework (e.g., stored procedures > dbt)
  • Continuously replicating data from an OLTP DB to OLAP DWH (e.g., MySQL > Redshift)

Data Development Testing

Test SQL code and preview changes by comparing development/staging environment data to production:

  1. Make a change to some SQL code
  2. Run the SQL code to create a new dataset
  3. Compare the dataset with its production version or another iteration

dbt

data-diff integrates with dbt Core to seamlessly compare local development to production datasets

data-development-testing

dbt Cloud users should check out Datafold's out-of-the-box deployment testing integration

👀 Watch 4-min demo video

Get started with data-diff & dbt

Also available in a VS Code Extension

Reach out on the dbt Slack in #tools-datafold for advice and support

How it works

When comparing the data, data-diff utilizes the resources of the underlying databases as much as possible. It has two primary modes of comparison:

joindiff

  • Recommended for comparing data within the same database
  • Uses the outer join operation to diff the rows as efficiently as possible within the same database
  • Fully relies on the underlying database engine for computation
  • Requires both datasets to be queryable with a single SQL query
  • Time complexity approximates JOIN operation and is largely independent of the number of differences in the dataset

hashdiff

  • Recommended for comparing datasets across different databases
  • Can also be helpful in diffing very large tables with few expected differences within the same database
  • Employs a divide-and-conquer algorithm based on hashing and binary search
  • Can diff data across distinct database engines, e.g., PostgreSQL <> Snowflake
  • Time complexity approximates COUNT(*) operation when there are few differences
  • Performance degrades when datasets have a large number of differences

More information about the algorithm and performance considerations can be found here

Get started

Validating dbt model changes between dev and prod

⚡ Looking to use data-diff in dbt development? Head over to our data-diff + dbt documentation to get started!

Compare data tables between databases

🔀 To compare data between databases, install data-diff with specific database adapters, e.g.:

pip install data-diff 'data-diff[postgresql,snowflake]' -U

Run data-diff with connection URIs. In the following example, we compare tables between PostgreSQL and Snowflake using hashdiff algorithm:

data-diff \
  postgresql://<username>:'<password>'@localhost:5432/<database> \
  <table> \
  "snowflake://<username>:<password>@<password>/<DATABASE>/<SCHEMA>?warehouse=<WAREHOUSE>&role=<ROLE>" \
  <TABLE> \
  -k <primary key column> \
  -c <columns to compare> \
  -w <filter condition>

Check out documentation for the full command reference.

Supported databases

Database Status Connection string
PostgreSQL >=10 🟢 postgresql://<user>:<password>@<host>:5432/<database>
MySQL 🟢 mysql://<user>:<password>@<hostname>:5432/<database>
Snowflake 🟢 "snowflake://<user>[:<password>]@<account>/<database>/<SCHEMA>?warehouse=<WAREHOUSE>&role=<role>[&authenticator=externalbrowser]"
BigQuery 🟢 bigquery://<project>/<dataset>
Redshift 🟢 redshift://<username>:<password>@<hostname>:5439/<database>
Oracle 🟡 oracle://<username>:<password>@<hostname>/servive_or_sid
Presto 🟡 presto://<username>:<password>@<hostname>:8080/<database>
Databricks 🟡 databricks://<http_path>:<access_token>@<server_hostname>/<catalog>/<schema>
Trino 🟡 trino://<username>:<password>@<hostname>:8080/<database>
Clickhouse 🟡 clickhouse://<username>:<password>@<hostname>:9000/<database>
Vertica 🟡 vertica://<username>:<password>@<hostname>:5433/<database>
DuckDB 🟡
ElasticSearch 📝
Planetscale 📝
Pinot 📝
Druid 📝
Kafka 📝
SQLite 📝
  • 🟢: Implemented and thoroughly tested.
  • 🟡: Implemented, but not thoroughly tested yet.
  • ⏳: Implementation in progress.
  • 📝: Implementation planned. Contributions welcome.

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Contributors

We thank everyone who contributed so far!


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License

This project is licensed under the terms of the MIT License.

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