Dropping data

When you are working with continuous aggregates, you can drop a view, or you can drop raw data from the underlying hypertable. Additionally, you need to be aware if a retention policy is likely to drop raw data from your hypertable that you need in your continuous aggregate.

Drop a continuous aggregate view

You can drop a continuous aggregate view using the DROP MATERIALIZED VIEW command. This command does not drop the data from the underlying hypertable.

Procedure: Dropping a continuous aggregate view

  1. From the psqlprompt, drop the view:

Drop raw data from a hypertable

If you drop data from a hypertable used in a continuous aggregate it can lead to problems with your continuous aggregate view. In many cases, dropping underlying data replaces the aggregate with NULL values, which can lead to unexpected results in your view.

You can drop data from a hypertable using drop_chunks in the usual way, but before you do so, always check that the chunk is not within the refresh window of a continuous aggregate that still needs the data. This is also important if you are manually refreshing a continuous aggregate. Calling refresh_continuous_aggregate on a region containing dropped chunks recalculates the aggregate without the dropped data.

If a continuous aggregate is refreshing when data is dropped because of a retention policy, the aggregate is updated to reflect the loss of data. If you need to retain the continuous aggregate after dropping the underlying data, set the start_offset value of the aggregate policy to a smaller interval than the drop_after parameter of the retention policy.

For more information, see the data retention documentation.

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