Redis XTRIM in Node.js (Detailed Guide w/ Code Examples)

Use Case(s)

XTRIM is a Redis command used to trim the size of a stream to a maximum number of elements. Common use cases include:

  • Limiting the memory footprint of streams by trimming old data.
  • Maintaining a fixed-size log or event history.

Code Examples

Example 1: Trimming a Stream by Maximum Length

const redis = require('redis'); const client = redis.createClient(); client.xadd('mystream', '*', 'field1', 'value1', 'field2', 'value2', err => { if (err) throw err; // Trim the stream to only keep the latest 1000 entries client.xtrim('mystream', 'MAXLEN', '~', 1000, (trimErr, res) => { if (trimErr) throw trimErr; console.log(`Stream trimmed, ${res} items removed.`); }); });

In this example, XTRIM is used with MAXLEN which means the stream will be trimmed to the specified length. The ~ argument indicates that the trim operation is approximate and Redis may remove slightly more than 1000 items to improve performance.

Example 2: Using XTRIM in a Transaction

const redis = require('redis'); const client = redis.createClient(); // Start a Redis transaction client.multi() .xadd('mystream', '*', 'field1', 'value1') .xtrim('mystream', 'MAXLEN', '~', 1000) .exec((err, replies) => { if (err) throw err; console.log(`Transaction completed with responses: ${replies}`); });

Here, xadd and xtrim are part of a multi/exec transaction, ensuring atomicity. If one command fails, none of the commands take effect.

Best Practices

  • Use the ~ option for better performance if an exact trim is not necessary.
  • Consider using XTRIM in a Lua script or transaction if you need to perform multiple operations atomically.

Common Mistakes

  • Not handling errors properly - always check for errors in callbacks.
  • Over-trimming or under-trimming due to not understanding how the ~ option affects the operation.


Q: When should I avoid using the ~ option with XTRIM? A: Avoid using the ~ option when you need precise control over the number of elements in the stream.

Q: Is XTRIM an expensive operation? A: It can be, especially on large streams. However, the ~ option can help mitigate performance costs by trimming less precisely but more efficiently.

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