Database migration to a new database platform or technology can be daunting for various reasons. One of the common concerns is database performance. It is hard to evaluate database performance early in the evaluation cycle without performing actual data migration and application changes. This becomes even more important in the case of Cloud Spanner where modernization is required at both the database and application layers. 

The traditional approach to evaluate database performance is to deploy the application and database together, migrate historical data to the new database and then simulate load tests by running an application on the new database. Doing all this for an early performance evaluation of Cloud Spanner may feel like a lot of effort.

In this post, we will explore a middle ground to performance testing using JMeter. Performance test Cloud Spanner for a custom workload before making application code changes and executing data migration. More detailed step-by-step guide is published here.

Goals

• Estimate the number of Cloud Spanner nodes needed (and get a cost estimate).

• Performance test the most frequently used set of queries and transactions.

• Demonstrate the ability to scale horizontally.

• Better understand the optimizations needed for schema and sql queries.

• Determine latency of DML operations.

Limitations

• You cannot test using non-java client libraries.

• It is more complex to test non-jdbc compliant features like mutations, parallel reads etc.

Preparing for performance tests

1. Identify top SQL queries, latency, frequency / hour and avg number of rows returned or updated for each. This information will also serve as a baseline for the current system.

2. Determine Cloud Spanner region / multi-region deployment. Ideally, load should be generated from the Cloud Spanner instance’s leader region for minimum latency and best performance. Read Demystifying Cloud Spanner multi-region configurations for more details on various configurations of Cloud Spanner.

3. Estimate the number of Cloud Spanner nodes required for a given workload based on (step 1). It is recommended to have a minimum of 2 nodes for linear scaling.
   Note: Peak performance numbers of regional performance and multi regional performance are published. It is based on a 1KB single row transaction with no secondary indexes.

4. Request quota for Cloud Spanner nodes on a given region / multi-region. It can take up to 1 business day. 

Setting up Cloud Spanner

Creating the schema for Cloud Spanner

You can use the following tools to generate a schema for Cloud Spanner if you are migrating from the following source databases. Alternatively, you can model the schema manually. Schema design has a huge performance impact, hence it is recommended to review the schema very carefully.

Note: Manual review and tuning of schema will be needed to optimize and mitigate potential hotspots. You will need to keep in mind schema design best practices when modeling your schema.

Populating seed data into Cloud Spanner

Performance of a database depends on the amount of data present. Existing data (and indexes) determines how much data is scanned on select queries and therefore performance. Hence, it is important to seed data into Cloud Spanner before performance testing. 

For most realistic results, data should be migrated from an existing production source. Sometimes you cannot do that due to schema changes. One way is to utilize a custom ETL job to export and transform data and then import into Cloud Spanner. Another alternative could be to mock seed data using JMeter(More details in later sections).

JMeter performance tests

Writing Tests

JMeter will interact with Cloud Spanner just like your application. It will perform DML operations the same way as your application does. Hence, tests need to simulate production like transactions. For example if a transaction is made up of insert and/or update statements in several tables within transaction boundaries then JMeter should mimic the same.

JMeter has the following hierarchy:

Test Plan > Thread Group(s) > Sampler(s) (aka test)

Test plan is a top level component. It can contain global properties and libraries (like jdbc driver etc).

Thread Group(s) are representative of a database transaction. It contains one or more sampler(s). All the samplers within a thread group execute serially.

Sampler(s) should represent a single DML call. If your transaction needs to have multiple dml calls, you should create multiple samplers. Typically you will use JDBC Sampler for database calls. You can also use JSR 223 Sampler as described here, in case you need to use mutations or parallel reads etc. Results from one sampler can be passed to the next, as in real world application.

Executing tests and collecting results

JMeter tests should be executed as physically close to Cloud Spanner instances as possible to minimize network latency. Therefore it is best to execute them from Compute Engine (via private service connect) from the same region as the Cloud Spanner instance. In-case of multi region Cloud Spanner, GCE instances should be created in the Leader Region of the Cloud Spanner instance for lowest network latency.

JMeter should be executed via command line, it is a CPU intensive application so make sure you have allocated enough resources on the VM.

Refer to the Cloud Spanner monitoring dashboard to ensure that your Cloud Spanner instance’s CPU utilization is at or below the recommended values. In addition, use introspection tools to investigate performance issues with your database. 

You might need to optimize your queries (add indexes) and re-execute tests in multiple waves to tune the performance as needed.

Try it yourself

Follow a detailed step by step tutorial on Measure Cloud Spanner performance test using JMeter to test Cloud Spanner performance yourself.