drop_chunks()

Removes data chunks whose time range falls completely before (or after) a specified time. Shows a list of the chunks that were dropped, in the same style as the show_chunks function.

Chunks are constrained by a start and end time and the start time is always before the end time. A chunk is dropped if its end time is older than the older_than timestamp or, if newer_than is given, its start time is newer than the newer_than timestamp.

Note that, because chunks are removed if and only if their time range falls fully before (or after) the specified timestamp, the remaining data may still contain timestamps that are before (or after) the specified one.

Chunks can only be dropped based on their time intervals. They cannot be dropped based on a hash partition.

The older_than and newer_than parameters can be specified in two ways:

• interval type: The cut-off point is computed as now() - older_than and similarly now() - newer_than. An error is returned if an INTERVAL is supplied and the time column is not one of a TIMESTAMP, TIMESTAMPTZ, or DATE.

• timestamp, date, or integer type: The cut-off point is explicitly given as a TIMESTAMP / TIMESTAMPTZ / DATE or as a SMALLINT / INT / BIGINT. The choice of timestamp or integer must follow the type of the hypertable's time column.

The created_before and created_after parameters can be specified in two ways:

• interval type: The cut-off point is computed as now() - created_before and similarly now() - created_after. This uses the chunk creation time relative to the current time for the filtering.

• timestamp, date, or integer type: The cut-off point is explicitly given as a TIMESTAMP / TIMESTAMPTZ / DATE or as a SMALLINT / INT / BIGINT. The choice of integer value must follow the type of the hypertable's partitioning column. Otherwise the chunk creation time is used for the filtering.

Warning

When using just an interval type, the function assumes that you are removing things in the past. If you want to remove data in the future, for example to delete erroneous entries, use a timestamp.

When both older_than and newer_than arguments are used, the function returns the intersection of the resulting two ranges. For example, specifying newer_than => 4 months and older_than => 3 months drops all chunks between 3 and 4 months old. Similarly, specifying newer_than => '2017-01-01' and older_than => '2017-02-01' drops all chunks between '2017-01-01' and '2017-02-01'. Specifying parameters that do not result in an overlapping intersection between two ranges results in an error.

When both created_before and created_after arguments are used, the function returns the intersection of the resulting two ranges. For example, specifying created_after => 4 monthsandcreated_before=> 3 months drops all chunks created between 3 and 4 months from now. Similarly, specifying created_after=> '2017-01-01'andcreated_before => '2017-02-01' drops all chunks created between '2017-01-01' and '2017-02-01'. Specifying parameters that do not result in an overlapping intersection between two ranges results in an error.

Note

The created_before/created_after parameters cannot be used together with older_than/newer_than.

Drop all chunks from hypertable conditions older than 3 months:

SELECT drop_chunks('conditions', INTERVAL '3 months');

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Example output:

drop_chunks
----------------------------------------
 _timescaledb_internal._hyper_3_5_chunk
 _timescaledb_internal._hyper_3_6_chunk
 _timescaledb_internal._hyper_3_7_chunk
 _timescaledb_internal._hyper_3_8_chunk
 _timescaledb_internal._hyper_3_9_chunk
(5 rows)

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Drop all chunks from hypertable conditions created before 3 months:

SELECT drop_chunks('conditions', created_before => now() -  INTERVAL '3 months');

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Drop all chunks more than 3 months in the future from hypertable conditions. This is useful for correcting data ingested with incorrect clocks:

SELECT drop_chunks('conditions', newer_than => now() + interval '3 months');

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Drop all chunks from hypertable conditions before 2017:

SELECT drop_chunks('conditions', '2017-01-01'::date);

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Drop all chunks from hypertable conditions before 2017, where time column is given in milliseconds from the UNIX epoch:

SELECT drop_chunks('conditions', 1483228800000);

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Drop all chunks older than 3 months ago and newer than 4 months ago from hypertable conditions:

SELECT drop_chunks('conditions', older_than => INTERVAL '3 months', newer_than => INTERVAL '4 months')

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Drop all chunks created 3 months ago and created 4 months before from hypertable conditions:

SELECT drop_chunks('conditions', created_before => INTERVAL '3 months', created_after => INTERVAL '4 months')

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Drop all chunks older than 3 months ago across all hypertables:

SELECT drop_chunks(format('%I.%I', hypertable_schema, hypertable_name)::regclass, INTERVAL '3 months')
  FROM timescaledb_information.hypertables;

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