Experimental Features

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This page lists the experimental features that are available in CockroachDB v21.2.

Warning:

This page describes experimental features. Their interfaces and outputs are subject to change, and there may be bugs.

If you encounter a bug, please file an issue.

Session variables

The table below lists the experimental session settings that are available. For a complete list of session variables, see SHOW {session variable}.

Variable	Default Value	Description
`enable_experimental_alter_column_type_general`	`'false'`	If set to `'true'`, enables column type altering for general cases, with some limitations.
`experimental_enable_hash_sharded_indexes`	`'off'`	If set to `'on'`, enables hash-sharded indexes with `USING HASH`.
`experimental_enable_temp_tables`	`'off'`	If set to `'on'`, enables temporary objects, including temporary tables, temporary views, and temporary sequences.

SQL statements

Keep SQL audit logs

Log all queries against a table to a file, for security purposes. For more information, see ALTER TABLE ... EXPERIMENTAL_AUDIT.

> ALTER TABLE t EXPERIMENTAL_AUDIT SET READ WRITE;

Relocate leases and replicas

You have the following options for controlling lease and replica location:

Relocate leases and replicas using EXPERIMENTAL_RELOCATE
Relocate just leases using EXPERIMENTAL_RELOCATE LEASE

For example, to distribute leases and ranges for N primary keys across N stores in the cluster, run a statement with the following structure:

> ALTER TABLE t EXPERIMENTAL_RELOCATE SELECT ARRAY[<storeid1>, <storeid2>, ..., <storeidN>], <primarykeycol1>, <primarykeycol2>, ..., <primarykeycolN>;

To relocate just the lease without moving the replicas, run a statement like the one shown below, which moves the lease for the range containing primary key 'foo' to store 1.

> ALTER TABLE t EXPERIMENTAL_RELOCATE LEASE SELECT 1, 'foo';

Show table fingerprints

Table fingerprints are used to compute an identification string of an entire table, for the purpose of gauging whether two tables have the same data. This is useful, for example, when restoring a table from backup.

Example:

> SHOW EXPERIMENTAL_FINGERPRINTS FROM TABLE t;

 index_name |     fingerprint
------------+---------------------
 primary    | 1999042440040364641
(1 row)

Turn on KV event tracing

Use session tracing (via SHOW TRACE FOR SESSION) to report the replicas of all KV events that occur during its execution.

Example:

> SET tracing = on;
> SELECT * from t;
> SET tracing = off;
> SHOW EXPERIMENTAL_REPLICA TRACE FOR SESSION;

            timestamp             | node_id | store_id | replica_id
----------------------------------+---------+----------+------------
 2018-10-18 15:50:13.345879+00:00 |       3 |        3 |          7
 2018-10-18 15:50:20.628383+00:00 |       2 |        2 |         26

Check for constraint violations with `SCRUB`

Checks the consistency of UNIQUE indexes, CHECK constraints, and more. Partially implemented; see cockroachdb/cockroach#10425 for details.

Note:

This example uses the users table from our open-source, fictional peer-to-peer vehicle-sharing application, MovR.

>  EXPERIMENTAL SCRUB table movr.users;

 job_uuid |        error_type        | database | table |                       primary_key                        |         timestamp         | repaired |                                                                                                                                                                         details
----------+--------------------------+----------+-------+----------------------------------------------------------+---------------------------+----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
          | index_key_decoding_error | movr     | users | ('boston','0009eeb5-d779-4bf8-b1bd-8566533b105c')        | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'06484 Christine Villages\\nGrantport, TN 01572'", "city": "'boston'", "credit_card": "'4634253150884'", "id": "'0009eeb5-d779-4bf8-b1bd-8566533b105c'", "name": "'Jessica Webb'"}}
          | index_key_decoding_error | movr     | users | ('los angeles','0001252c-fc16-4006-b6dc-c6b1a0fd1f5b')   | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'91309 Warner Springs\\nLake Danielmouth, PR 33400'", "city": "'los angeles'", "credit_card": "'3584736360686445'", "id": "'0001252c-fc16-4006-b6dc-c6b1a0fd1f5b'", "name": "'Rebecca Gibson'"}}
          | index_key_decoding_error | movr     | users | ('new york','000169a5-e337-4441-b664-dae63e682980')      | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'0787 Christopher Highway Apt. 363\\nHamptonmouth, TX 91864-2620'", "city": "'new york'", "credit_card": "'4578562547256688'", "id": "'000169a5-e337-4441-b664-dae63e682980'", "name": "'Christopher Johnson'"}}
          | index_key_decoding_error | movr     | users | ('paris','00089fc4-e5b1-48f6-9f0b-409905f228c4')         | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'46735 Martin Summit\\nMichaelview, OH 10906-5889'", "city": "'paris'", "credit_card": "'5102207609888778'", "id": "'00089fc4-e5b1-48f6-9f0b-409905f228c4'", "name": "'Nicole Fuller'"}}
          | index_key_decoding_error | movr     | users | ('rome','000209fc-69a1-4dd5-8053-3b5e5769876d')          | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'473 Barrera Vista Apt. 890\\nYeseniaburgh, CO 78087'", "city": "'rome'", "credit_card": "'3534605564661093'", "id": "'000209fc-69a1-4dd5-8053-3b5e5769876d'", "name": "'Sheryl Shea'"}}
          | index_key_decoding_error | movr     | users | ('san francisco','00058767-1e83-4e18-999f-13b5a74d7225') | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'5664 Acevedo Drive Suite 829\\nHernandezview, MI 13516'", "city": "'san francisco'", "credit_card": "'376185496850202'", "id": "'00058767-1e83-4e18-999f-13b5a74d7225'", "name": "'Kevin Turner'"}}
          | index_key_decoding_error | movr     | users | ('seattle','0002e904-1256-4528-8b5f-abad16e695ff')       | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'81499 Samuel Crescent Suite 631\\nLake Christopherborough, PR 50401'", "city": "'seattle'", "credit_card": "'38743493725890'", "id": "'0002e904-1256-4528-8b5f-abad16e695ff'", "name": "'Mark Williams'"}}
          | index_key_decoding_error | movr     | users | ('washington dc','00007caf-2014-4696-85b0-840e7d8b6db9') | 2018-10-18 16:00:38.65916 | f        | {"error_message": "key ordering did not match datum ordering. IndexDescriptor=ASC", "index_name": "primary", "row_data": {"address": "e'4578 Holder Trafficway\\nReynoldsside, IL 23520-7418'", "city": "'washington dc'", "credit_card": "'30454993082943'", "id": "'00007caf-2014-4696-85b0-840e7d8b6db9'", "name": "'Marie Miller'"}}
(8 rows)

Show range information for a specific row

The SHOW RANGE ... FOR ROW statement shows information about a range for a particular row of data. This information is useful for verifying how SQL data maps to underlying ranges, and where the replicas for a range are located.

Functions and Operators

The table below lists the experimental SQL functions and operators available in CockroachDB. For more information, see each function's documentation at Functions and Operators.

Function	Description
`experimental_strftime`	Format time using standard `strftime` notation.
`experimental_strptime`	Format time using standard `strptime` notation.
`experimental_uuid_v4()`	Return a UUID.

Alter column types

CockroachDB supports altering the column types of existing tables, with certain limitations. For more information, see Altering column data types.

Temporary objects

Support for temporary tables, temporary views, and temporary sequences is currently experimental in CockroachDB. If you create too many temporary objects in a session, the performance of DDL operations will degrade. Performance limitations could persist long after creating the temporary objects. For more details, see cockroachdb/cockroach#46260.

Hash-sharded indexes

CockroachDB supports hash-sharded indexes with the USING HASH keywords. Hash-sharded indexes distribute sequential traffic uniformly across ranges, eliminating single-range hot spots and improving write performance on sequentially-keyed indexes at a small cost to read performance. For more information, see Hash-sharded indexes.

Password authentication without TLS

For deployments where transport security is already handled at the infrastructure level (e.g., IPSec with DMZ), and TLS-based transport security is not possible or not desirable, CockroachDB now supports delegating transport security to the infrastructure with the new experimental flag --accept-sql-without-tls for cockroach start.

With this flag, SQL clients can establish a session over TCP without a TLS handshake. They still need to present valid authentication credentials, for example a password in the default configuration. Different authentication schemes can be further configured as per server.host_based_authentication.configuration.

Example:

  $ cockroach sql --user=jpointsman --insecure

    # Welcome to the CockroachDB SQL shell.
    # All statements must be terminated by a semicolon.
    # To exit, type: \q.
    #
    Enter password:

Changefeed metrics labels

To measure metrics per changefeed, define a "metrics label" to which one or multiple changefeed(s) will increment each changefeed metric. Metrics label information is sent with time-series metrics to http://{host}:{http-port}/_status/vars, viewable via the Prometheus endpoint. An aggregated metric of all changefeeds is also measured.

It is necessary to consider the following when applying metrics labels to changefeeds:

Metrics labels are not available in CockroachDB Cloud.
The COCKROACH_EXPERIMENTAL_ENABLE_PER_CHANGEFEED_METRICS environment variable must be specified to use this feature.
The server.child_metrics.enabled cluster setting must be set to true before using the metrics_label option.
Metrics label information is sent to the _status/vars endpoint, but will not show up in debug.zip or the DB Console.
Introducing labels to isolate a changefeed's metrics can increase cardinality significantly. There is a limit of 1024 unique labels in place to prevent cardinality explosion. That is, when labels are applied to high-cardinality data (data with a higher number of unique values), each changefeed with a label then results in more metrics data to multiply together, which will grow over time. This will have an impact on performance as the metric-series data per changefeed quickly populates against its label.
The maximum length of a metrics label is 128 bytes.

For usage details, see the Monitor and Debug Changefeeds page.

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Experimental Features

Session variables

SQL statements

Keep SQL audit logs

Relocate leases and replicas

Show table fingerprints

Turn on KV event tracing

Check for constraint violations with `SCRUB`

Show range information for a specific row

Functions and Operators

Alter column types

Temporary objects

Hash-sharded indexes

Password authentication without TLS

Changefeed metrics labels

See Also

Experimental Features

Session variables

SQL statements

Keep SQL audit logs

Relocate leases and replicas

Show table fingerprints

Turn on KV event tracing

Check for constraint violations with SCRUB

Show range information for a specific row

Functions and Operators

Alter column types

Temporary objects

Hash-sharded indexes

Password authentication without TLS

Changefeed metrics labels

See Also

Check for constraint violations with `SCRUB`