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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.

Required Arguments

NameTypeDescription
relationREGCLASSHypertable or continuous aggregate from which to drop chunks.
older_thanINTERVALSpecification of cut-off point where any full chunks older than this timestamp should be removed.

Optional Arguments

NameTypeDescription
newer_thanINTERVALSpecification of cut-off point where any full chunks newer than this timestamp should be removed.
verboseBOOLEANSetting to true will display messages about the progress of the reorder command. Defaults to false.

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 will be 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.

warning

When using just an interval type, the function assumes that you are are removing things _in the past_. If you want to remove data in the future (i.e., erroneous entries), use a timestamp.

When both 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 will drop all full chunks that are between 3 and 4 months old. Similarly, specifying newer_than => '2017-01-01' and older_than => '2017-02-01' will drop all full chunks between '2017-01-01' and '2017-02-01'. Specifying parameters that do not result in an overlapping intersection between two ranges will result in an error.

Sample Usage

Drop all chunks from hypertable conditions older than 3 months:

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

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)

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');

Drop all chunks from hypertable conditions before 2017:

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

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

SELECT drop_chunks('conditions', 1483228800000);

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')

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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