UNSPLIT AT

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The UNSPLIT AT statement removes a split enforcement on a range split, at a specified row in a table or index.

Removing a split enforcement from a table or index ("unsplitting") allows CockroachDB to merge ranges as needed, to help improve your cluster's performance. For more information, see Range Merges.

Synopsis

ALTER TABLE table_name UNSPLIT AT select_stmt ALL
ALTER INDEX table_name @ index_name UNSPLIT AT select_stmt ALL

Required privileges

The user must have the INSERT privilege on the table or index.

Parameters

Parameter Description
table_name The name of the table that you want to unsplit.
table_name @ index_name
standalone_index_name
The name of the index that you want to unsplit.
select_stmt A selection query that produces one or more rows at which to unsplit a table or index.

Examples

Setup

The following examples use MovR, a fictional vehicle-sharing application, to demonstrate CockroachDB SQL statements. For more information about the MovR example application and dataset, see MovR: A Global Vehicle-sharing App.

To follow along, run cockroach demo to start a temporary, in-memory cluster with the movr dataset preloaded:

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$ cockroach demo

Unsplit a table

Suppose that you want MovR to offer ride-sharing services, in addition to vehicle-sharing services. Some users need to sign up to be drivers, so you need a drivers table to store driver information.

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> CREATE TABLE drivers (
    id UUID DEFAULT gen_random_uuid(),
    city STRING,
    name STRING,
    dl STRING DEFAULT left(md5(random()::text),8) UNIQUE CHECK (LENGTH(dl) < 9),
    address STRING,
    CONSTRAINT "primary" PRIMARY KEY (city ASC, dl ASC)
);

The table's compound primary key is on the city and dl columns. Note that the table automatically generates an id and a dl using supported SQL functions, if they are not provided.

Because this table has several columns in common with the users table, you can populate the table with values from the users table with an INSERT statement:

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> INSERT INTO drivers (id, city, name, address)
    SELECT id, city, name, address FROM users;

At this point, just one range contains the data in the drivers table.

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> SHOW RANGES FROM TABLE drivers;
  start_key | end_key | range_id | range_size_mb | lease_holder | lease_holder_locality | replicas |    replica_localities
------------+---------+----------+---------------+--------------+-----------------------+----------+---------------------------
  NULL      | NULL    |       74 |      0.007218 |            1 | region=us-east1,az=b  | {1}      | {"region=us-east1,az=b"}
(1 row)

You can split the table based on the compound primary key. Note that you do not have to specify the entire value for the primary key, just the prefix.

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> ALTER TABLE drivers SPLIT AT VALUES ('new york', '3'), ('new york', '7'), ('chicago', '3'), ('chicago', '7'), ('seattle', '3'), ('seattle', '7');
                     key                    |     pretty      |    split_enforced_until
--------------------------------------------+-----------------+-----------------------------
  \xc3\x89\x12new york\x00\x01\x123\x00\x01 | /"new york"/"3" | 2262-04-11 23:47:16.854776
  \xc3\x89\x12new york\x00\x01\x127\x00\x01 | /"new york"/"7" | 2262-04-11 23:47:16.854776
  \xc3\x89\x12chicago\x00\x01\x123\x00\x01  | /"chicago"/"3"  | 2262-04-11 23:47:16.854776
  \xc3\x89\x12chicago\x00\x01\x127\x00\x01  | /"chicago"/"7"  | 2262-04-11 23:47:16.854776
  \xc3\x89\x12seattle\x00\x01\x123\x00\x01  | /"seattle"/"3"  | 2262-04-11 23:47:16.854776
  \xc3\x89\x12seattle\x00\x01\x127\x00\x01  | /"seattle"/"7"  | 2262-04-11 23:47:16.854776
(6 rows)

The crdb_internal.ranges view contains additional information about ranges in your CockroachDB cluster, including the expiration of the split enforcement.

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> SELECT range_id, start_pretty, end_pretty, split_enforced_until FROM crdb_internal.ranges WHERE table_name='drivers';
  range_id |        start_pretty        |         end_pretty         |    split_enforced_until
-----------+----------------------------+----------------------------+-----------------------------
        74 | /Table/59                  | /Table/59/1/"chicago"/"3"  | NULL
        77 | /Table/59/1/"chicago"/"3"  | /Table/59/1/"chicago"/"7"  | 2262-04-11 23:47:16.854776
        78 | /Table/59/1/"chicago"/"7"  | /Table/59/1/"new york"/"3" | 2262-04-11 23:47:16.854776
        75 | /Table/59/1/"new york"/"3" | /Table/59/1/"new york"/"7" | 2262-04-11 23:47:16.854776
        76 | /Table/59/1/"new york"/"7" | /Table/59/1/"seattle"/"3"  | 2262-04-11 23:47:16.854776
        79 | /Table/59/1/"seattle"/"3"  | /Table/59/1/"seattle"/"7"  | 2262-04-11 23:47:16.854776
        80 | /Table/59/1/"seattle"/"7"  | /Max                       | 2262-04-11 23:47:16.854776
(7 rows)

Now unsplit the table to remove the split enforcements:

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> ALTER TABLE drivers UNSPLIT AT VALUES ('new york', '3'), ('new york', '7'), ('chicago', '3'), ('chicago', '7'), ('seattle', '3'), ('seattle', '7');
                     key                    |           pretty
--------------------------------------------+-----------------------------
  \xc3\x89\x12new york\x00\x01\x123\x00\x01 | /Table/59/1/"new york"/"3"
  \xc3\x89\x12new york\x00\x01\x127\x00\x01 | /Table/59/1/"new york"/"7"
  \xc3\x89\x12chicago\x00\x01\x123\x00\x01  | /Table/59/1/"chicago"/"3"
  \xc3\x89\x12chicago\x00\x01\x127\x00\x01  | /Table/59/1/"chicago"/"7"
  \xc3\x89\x12seattle\x00\x01\x123\x00\x01  | /Table/59/1/"seattle"/"3"
  \xc3\x89\x12seattle\x00\x01\x127\x00\x01  | /Table/59/1/"seattle"/"7"
(6 rows)
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> SELECT range_id, start_pretty, end_pretty, split_enforced_until FROM crdb_internal.ranges WHERE table_name='drivers';
  range_id |        start_pretty        |         end_pretty         | split_enforced_until
-----------+----------------------------+----------------------------+-----------------------
        74 | /Table/59                  | /Table/59/1/"chicago"/"3"  | NULL
        77 | /Table/59/1/"chicago"/"3"  | /Table/59/1/"chicago"/"7"  | NULL
        78 | /Table/59/1/"chicago"/"7"  | /Table/59/1/"new york"/"3" | NULL
        75 | /Table/59/1/"new york"/"3" | /Table/59/1/"new york"/"7" | NULL
        76 | /Table/59/1/"new york"/"7" | /Table/59/1/"seattle"/"3"  | NULL
        79 | /Table/59/1/"seattle"/"3"  | /Table/59/1/"seattle"/"7"  | NULL
        80 | /Table/59/1/"seattle"/"7"  | /Max                       | NULL
(7 rows)

The drivers table is still split into ranges at specific primary key column values, but the split_enforced_until column is now NULL for all ranges in the table. The split is no longer enforced, and CockroachDB can merge the data in the table as needed.

Unsplit an index

Add a new secondary index to the rides table, on the revenue column, and then split the table ranges by secondary index values:

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> CREATE INDEX revenue_idx ON rides(revenue);
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> ALTER INDEX rides@revenue_idx SPLIT AT VALUES (25.00), (50.00), (75.00);
         key        | pretty |        split_enforced_until
--------------------+--------+--------------------------------------
  \277\214*2\000    | /25    | 2262-04-11 23:47:16.854776+00:00:00
  \277\214*d\000    | /5E+1  | 2262-04-11 23:47:16.854776+00:00:00
  \277\214*\226\000 | /75    | 2262-04-11 23:47:16.854776+00:00:00
(3 rows)
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> SELECT range_id, start_pretty, end_pretty, split_enforced_until FROM crdb_internal.ranges WHERE table_name='rides';
  range_id |                                        start_pretty                                         |                                         end_pretty                                          |        split_enforced_until
-----------+---------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------+--------------------------------------
        39 | /Table/55                                                                                   | /Table/55/1/"amsterdam"/"\xc5\x1e\xb8Q\xeb\x85@\x00\x80\x00\x00\x00\x00\x00\x01\x81"        | NULL
        56 | /Table/55/1/"amsterdam"/"\xc5\x1e\xb8Q\xeb\x85@\x00\x80\x00\x00\x00\x00\x00\x01\x81"        | /Table/55/1/"boston"/"8Q\xeb\x85\x1e\xb8B\x00\x80\x00\x00\x00\x00\x00\x00n"                 | 2262-04-11 23:47:16.854776+00:00:00
        55 | /Table/55/1/"boston"/"8Q\xeb\x85\x1e\xb8B\x00\x80\x00\x00\x00\x00\x00\x00n"                 | /Table/55/1/"los angeles"/"\xa8\xf5\u008f\\(H\x00\x80\x00\x00\x00\x00\x00\x01J"             | 2262-04-11 23:47:16.854776+00:00:00
        53 | /Table/55/1/"los angeles"/"\xa8\xf5\u008f\\(H\x00\x80\x00\x00\x00\x00\x00\x01J"             | /Table/55/1/"new york"/"\x1c(\xf5\u008f\\I\x00\x80\x00\x00\x00\x00\x00\x007"                | 2262-04-11 23:47:16.854776+00:00:00
        66 | /Table/55/1/"new york"/"\x1c(\xf5\u008f\\I\x00\x80\x00\x00\x00\x00\x00\x007"                | /Table/55/1/"paris"/"\xe1G\xae\x14z\xe1H\x00\x80\x00\x00\x00\x00\x00\x01\xb8"               | 2262-04-11 23:47:16.854776+00:00:00
        52 | /Table/55/1/"paris"/"\xe1G\xae\x14z\xe1H\x00\x80\x00\x00\x00\x00\x00\x01\xb8"               | /Table/55/1/"san francisco"/"\x8c\xcc\xcc\xcc\xcc\xcc@\x00\x80\x00\x00\x00\x00\x00\x01\x13" | 2262-04-11 23:47:16.854776+00:00:00
        65 | /Table/55/1/"san francisco"/"\x8c\xcc\xcc\xcc\xcc\xcc@\x00\x80\x00\x00\x00\x00\x00\x01\x13" | /Table/55/1/"seattle"/"p\xa3\xd7\n=pD\x00\x80\x00\x00\x00\x00\x00\x00\xdc"                  | 2262-04-11 23:47:16.854776+00:00:00
        64 | /Table/55/1/"seattle"/"p\xa3\xd7\n=pD\x00\x80\x00\x00\x00\x00\x00\x00\xdc"                  | /Table/55/1/"washington dc"/"Tz\xe1G\xae\x14L\x00\x80\x00\x00\x00\x00\x00\x00\xa5"          | 2262-04-11 23:47:16.854776+00:00:00
        54 | /Table/55/1/"washington dc"/"Tz\xe1G\xae\x14L\x00\x80\x00\x00\x00\x00\x00\x00\xa5"          | /Table/55/4                                                                                 | 2262-04-11 23:47:16.854776+00:00:00
        68 | /Table/55/4                                                                                 | /Table/55/4/25                                                                              | 2021-04-08 16:27:45.201336+00:00:00
        69 | /Table/55/4/25                                                                              | /Table/55/4/5E+1                                                                            | 2262-04-11 23:47:16.854776+00:00:00
        70 | /Table/55/4/5E+1                                                                            | /Table/55/4/75                                                                              | 2262-04-11 23:47:16.854776+00:00:00
        71 | /Table/55/4/75                                                                              | /Table/56                                                                                   | 2262-04-11 23:47:16.854776+00:00:00
(13 rows)

Now unsplit the index to remove the split enforcements:

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> ALTER INDEX rides@revenue_idx UNSPLIT AT VALUES (25.00), (50.00), (75.00);
         key        |      pretty
--------------------+-------------------
  \277\214*2\000    | /Table/55/4/25
  \277\214*d\000    | /Table/55/4/5E+1
  \277\214*\226\000 | /Table/55/4/75
(3 rows)
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> SELECT range_id, start_pretty, end_pretty, split_enforced_until FROM crdb_internal.ranges WHERE table_name='rides';
  range_id |                                        start_pretty                                         |                                         end_pretty                                          |        split_enforced_until
-----------+---------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------+--------------------------------------
        39 | /Table/55                                                                                   | /Table/55/1/"amsterdam"/"\xc5\x1e\xb8Q\xeb\x85@\x00\x80\x00\x00\x00\x00\x00\x01\x81"        | NULL
        56 | /Table/55/1/"amsterdam"/"\xc5\x1e\xb8Q\xeb\x85@\x00\x80\x00\x00\x00\x00\x00\x01\x81"        | /Table/55/1/"boston"/"8Q\xeb\x85\x1e\xb8B\x00\x80\x00\x00\x00\x00\x00\x00n"                 | 2262-04-11 23:47:16.854776+00:00:00
        55 | /Table/55/1/"boston"/"8Q\xeb\x85\x1e\xb8B\x00\x80\x00\x00\x00\x00\x00\x00n"                 | /Table/55/1/"los angeles"/"\xa8\xf5\u008f\\(H\x00\x80\x00\x00\x00\x00\x00\x01J"             | 2262-04-11 23:47:16.854776+00:00:00
        53 | /Table/55/1/"los angeles"/"\xa8\xf5\u008f\\(H\x00\x80\x00\x00\x00\x00\x00\x01J"             | /Table/55/1/"new york"/"\x1c(\xf5\u008f\\I\x00\x80\x00\x00\x00\x00\x00\x007"                | 2262-04-11 23:47:16.854776+00:00:00
        66 | /Table/55/1/"new york"/"\x1c(\xf5\u008f\\I\x00\x80\x00\x00\x00\x00\x00\x007"                | /Table/55/1/"paris"/"\xe1G\xae\x14z\xe1H\x00\x80\x00\x00\x00\x00\x00\x01\xb8"               | 2262-04-11 23:47:16.854776+00:00:00
        52 | /Table/55/1/"paris"/"\xe1G\xae\x14z\xe1H\x00\x80\x00\x00\x00\x00\x00\x01\xb8"               | /Table/55/1/"san francisco"/"\x8c\xcc\xcc\xcc\xcc\xcc@\x00\x80\x00\x00\x00\x00\x00\x01\x13" | 2262-04-11 23:47:16.854776+00:00:00
        65 | /Table/55/1/"san francisco"/"\x8c\xcc\xcc\xcc\xcc\xcc@\x00\x80\x00\x00\x00\x00\x00\x01\x13" | /Table/55/1/"seattle"/"p\xa3\xd7\n=pD\x00\x80\x00\x00\x00\x00\x00\x00\xdc"                  | 2262-04-11 23:47:16.854776+00:00:00
        64 | /Table/55/1/"seattle"/"p\xa3\xd7\n=pD\x00\x80\x00\x00\x00\x00\x00\x00\xdc"                  | /Table/55/1/"washington dc"/"Tz\xe1G\xae\x14L\x00\x80\x00\x00\x00\x00\x00\x00\xa5"          | 2262-04-11 23:47:16.854776+00:00:00
        54 | /Table/55/1/"washington dc"/"Tz\xe1G\xae\x14L\x00\x80\x00\x00\x00\x00\x00\x00\xa5"          | /Table/55/4                                                                                 | 2262-04-11 23:47:16.854776+00:00:00
        68 | /Table/55/4                                                                                 | /Table/55/4/25                                                                              | 2021-04-08 16:27:45.201336+00:00:00
        69 | /Table/55/4/25                                                                              | /Table/55/4/5E+1                                                                            | NULL
        70 | /Table/55/4/5E+1                                                                            | /Table/55/4/75                                                                              | NULL
        71 | /Table/55/4/75                                                                              | /Table/56                                                                                   | NULL
(13 rows)

The table is still split into ranges at 25.00, 50.00, and 75.00, but the split_enforced_until column is now NULL for all ranges in the table. The split is no longer enforced, and CockroachDB can merge the data in the table as needed.

See also


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