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ALTER SETTINGS PROFILE

Changes settings profiles.

Syntax:

ALTER SETTINGS PROFILE [IF EXISTS] name1 [RENAME TO new_name |, name2 [,...]]
    [ON CLUSTER cluster_name]
    [SETTINGS variable [= value] [MIN [=] min_value] [MAX [=] max_value] [CONST|READONLY|WRITABLE|CHANGEABLE_IN_READONLY] | INHERIT 'profile_name'] [,...]
    [ADD|MODIFY SETTINGS variable [= value] [MIN [=] min_value] [MAX [=] max_value] [CONST|READONLY|WRITABLE|CHANGEABLE_IN_READONLY] [,...]
    [DROP SETTINGS variable [,...] ]
    [ADD PROFILES 'profile_name' [,...] ]
    [DROP PROFILES 'profile_name' [,...] ]
    [DROP ALL SETTINGS]
    [DROP ALL PROFILES]
    [TO {{role1 | user1 [, role2 | user2 ...]} | NONE | ALL | ALL EXCEPT {role1 | user1 [, role2 | user2 ...]}}]

ON CLUSTER clause allows altering settings profiles on a cluster, see Distributed DDL.

Replacing vs. modifying settings​

ALTER SETTINGS PROFILE supports two different ways of changing the settings and the parent (inherited) profiles of a profile. They behave very differently, so it is important to pick the right one.

Replacing form: bare SETTINGS / INHERIT​

A bare SETTINGS clause (without ADD, MODIFY or DROP) replaces the entire settings list and all parent profiles of the profile with exactly what you list. Anything previously present but not listed is silently dropped — there is no warning.

CREATE SETTINGS PROFILE OR REPLACE p
    SETTINGS max_execution_time = 10, enable_lazy_columns_replication = 1;

ALTER SETTINGS PROFILE p SETTINGS max_memory_usage = 16106127360;

SHOW CREATE SETTINGS PROFILE p;
-- → CREATE SETTINGS PROFILE p SETTINGS max_memory_usage = 16106127360
-- max_execution_time and enable_lazy_columns_replication are gone.
Note

Because the bare SETTINGS form is a full replace, using it to "override one setting" on top of a populated base profile will drop every other setting (and every parent profile) on that profile. If you only want to change a single setting while keeping the rest, use the incremental MODIFY/ADD/DROP form described below.

This is the same behavior as SETTINGS in CREATE SETTINGS PROFILE: the clause defines the complete settings list.

Incremental form: ADD / MODIFY / DROP​

The ADD, MODIFY and DROP keywords change individual entries while leaving everything else on the profile untouched:

  • ADD SETTINGS variable = value [constraints] — adds a setting that is not yet present.
  • MODIFY SETTINGS variable = value [constraints] — replaces a single setting's entry. The whole entry (value and constraints) is overwritten, so re-specify MIN/MAX/READONLY/etc. if you want to keep them.
  • DROP SETTINGS variable [,...] — removes the listed settings.
  • ADD PROFILES 'profile_name' [,...] / DROP PROFILES 'profile_name' [,...] — add or remove parent (inherited) profiles.
  • DROP ALL SETTINGS / DROP ALL PROFILES — remove all settings or all parent profiles.

Several of these clauses can be combined in a single statement, for example DROP SETTINGS a ADD SETTINGS b = 1.

Examples​

Override a single setting while preserving the rest of a populated profile:

ALTER SETTINGS PROFILE p MODIFY SETTINGS max_memory_usage = 16106127360;

Add a new constrained setting and drop another one:

ALTER SETTINGS PROFILE my_profile
    DROP SETTINGS readonly
    ADD SETTINGS max_threads = 8 MIN 4 MAX 16 WRITABLE;

Manage parent profiles incrementally:

ALTER SETTINGS PROFILE my_profile ADD PROFILES p1;
ALTER SETTINGS PROFILE my_profile DROP PROFILES p1;

Always verify the result with SHOW CREATE SETTINGS PROFILE:

SHOW CREATE SETTINGS PROFILE my_profile;

Incremental vs full replacement​

Note

A bare SETTINGS clause removes all existing settings and all inherited (parent) profiles from the profile before applying the new ones.

To change a single setting while keeping the rest, use ADD SETTINGS or MODIFY SETTINGS (see examples below).

ADD vs MODIFY​

Both ADD SETTINGS and MODIFY SETTINGS preserve the other settings in the profile, but they treat an existing entry for the same setting differently:

  • ADD SETTINGS variable = value ... first drops any existing entry for variable and then inserts the new one. It therefore replaces the value together with all constraints of that setting. Any previously defined MIN, MAX, or writability (READONLY/WRITABLE/CONST/CHANGEABLE_IN_READONLY) for variable that you do not repeat is discarded.
  • MODIFY SETTINGS variable = value ... merges field by field: it overrides only the fields you actually specify (the value, or MIN, or MAX, or the writability) and keeps the other fields of that setting as they were.
Tip

In short, use MODIFY SETTINGS when you only want to tweak one aspect of a setting (e.g. just the value, while keeping an existing MAX); use ADD SETTINGS when you want to redefine a setting from scratch.

Examples​

Create a profile to use in the examples below:

CREATE SETTINGS PROFILE OR REPLACE p SETTINGS max_execution_time = 60;

MODIFY SETTINGS​

Add or change a single setting while keeping the others:

ALTER SETTINGS PROFILE p MODIFY SETTINGS max_memory_usage = 20000000000;
SHOW CREATE SETTINGS PROFILE p;
-- CREATE SETTINGS PROFILE p SETTINGS
--     max_execution_time = 60,
--     max_memory_usage = 20000000000

Because MODIFY merges field by field, changing only the value of a setting keeps its existing constraints:

ALTER SETTINGS PROFILE p MODIFY SETTINGS max_memory_usage = 20000000000 MAX 30000000000;
ALTER SETTINGS PROFILE p MODIFY SETTINGS max_memory_usage = 25000000000;
SHOW CREATE SETTINGS PROFILE p;
-- ... max_memory_usage = 25000000000 MAX 30000000000  -- the MAX constraint is preserved

ADD SETTINGS​

Add a setting (also keeping the others), redefining it completely if it already exists:

ALTER SETTINGS PROFILE p ADD SETTINGS max_threads = 8 MAX 16 READONLY;

Unlike MODIFY, re-running ADD with only a value drops the previously defined constraints for that setting:

ALTER SETTINGS PROFILE p ADD SETTINGS max_threads = 4;
SHOW CREATE SETTINGS PROFILE p;
-- ... max_threads = 4   -- the MAX and READONLY constraints are gone

DROP SETTINGS​

Remove one or more named settings:

ALTER SETTINGS PROFILE p DROP SETTINGS max_threads;

Remove all settings at once:

ALTER SETTINGS PROFILE p DROP ALL SETTINGS;

Working with inherited profiles​

Add or remove parent (inherited) profiles without affecting the profile's own settings:

ALTER SETTINGS PROFILE p ADD PROFILES base_profile;
ALTER SETTINGS PROFILE p DROP PROFILES base_profile;
ALTER SETTINGS PROFILE p DROP ALL PROFILES;