About data retention

In time-series applications, data often becomes less useful as it gets older. If you don’t need your historical data, you can delete it once it reaches a certain age. TimescaleDB lets you set up automatic data retention policies to discard old data. You can also fine-tune data retention by manually dropping chunks.

Often, you want to keep summaries of your historical data, but you don’t need the raw data. You can downsample your older data by combining data retention with continuous aggregates.

Drop data by chunk

TimescaleDB data retention works on chunks, not on rows. Deleting data row-by-row, for example with the PostgreSQL DELETE command, can be slow. But dropping data by the chunk is faster, because it deletes an entire file from disk. It doesn’t need garbage collection and defragmentation.

Whether you use a policy or manually drop chunks, TimescaleDB drops data by the chunk. It only drops chunks where all the data is wihin the specified time range.

For example, consider the setup where you have 3 chunks containing data:

1. More than 36 hours old
2. Between 12 and 36 hours old
3. From the last 12 hours

You manually drop chunks older than 24 hours. Only the oldest chunk is deleted. The middle chunk is retained, because it contains some data newer than 24 hours. No individual rows are deleted from that chunk.