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Clustering a table means reordering it according to an index. This operation requires an exclusive lock and extensive processing time. On large hypertables with many chunks, CLUSTER risks blocking a lot of operations by holding locks for a long time. This is alleviated by processing each chunk in a new transaction, ensuring locks are only held on one chunk at a time.
43 lines
1.2 KiB
SQL
43 lines
1.2 KiB
SQL
CREATE TABLE cluster_test(time timestamptz, temp float, location int);
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SELECT create_hypertable('cluster_test', 'time', chunk_time_interval => interval '1 day');
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-- Show default indexes
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SELECT * FROM test.show_indexes('cluster_test');
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-- Create two chunks
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INSERT INTO cluster_test VALUES ('2017-01-20T09:00:01', 23.4, 1),
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('2017-01-21T09:00:01', 21.3, 2);
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-- Run cluster
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CLUSTER VERBOSE cluster_test USING cluster_test_time_idx;
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-- Create a third chunk
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INSERT INTO cluster_test VALUES ('2017-01-22T09:00:01', 19.5, 3);
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-- Show clustered indexes
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SELECT indexrelid::regclass, indisclustered
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FROM pg_index
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WHERE indisclustered = true;
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-- Recluster just our table
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CLUSTER VERBOSE cluster_test;
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-- Show clustered indexes, including new chunk
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SELECT indexrelid::regclass, indisclustered
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FROM pg_index
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WHERE indisclustered = true;
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-- Recluster all tables (although will only be our test table)
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CLUSTER VERBOSE;
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-- Change the clustered index
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CREATE INDEX ON cluster_test (time, location);
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CLUSTER VERBOSE cluster_test using cluster_test_time_location_idx;
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-- Show updated clustered indexes
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SELECT indexrelid::regclass, indisclustered
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FROM pg_index
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WHERE indisclustered = true;
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