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Information schema

information_schema is a special schema that contains virtual tables which are read-only and can be queried to get information about the state of the cluster.

Table of contents

Access

When the user management is enabled, accessing the information_schema is open to all users and it does not require any privileges.

However, being able to query information_schema tables will not allow the user to retrieve all the rows in the table, as it can contain information related to tables over which the connected user does not have any privileges. The only rows that will be returned will be the ones the user is allowed to access.

For example, if the user john has any privilege on the doc.books table but no privilege at all on doc.locations, when john issues a SELECT * FROM information_schema.tables statement, the tables information related to the doc.locations table will not be returned.

Virtual tables

tables

The information_schema.tables virtual table can be queried to get a list of all available tables and views and their settings, such as number of shards or number of replicas.

cr> SELECT table_schema, table_name, table_type, number_of_shards, number_of_replicas
... FROM information_schema.tables
... ORDER BY table_schema ASC, table_name ASC;
+--------------------+-------------------------+------------+------------------+--------------------+
| table_schema       | table_name              | table_type | number_of_shards | number_of_replicas |
+--------------------+-------------------------+------------+------------------+--------------------+
| doc                | galaxies                | VIEW       |             NULL | NULL               |
| doc                | locations               | BASE TABLE |                2 | 0                  |
| doc                | partitioned_table       | BASE TABLE |                4 | 0-1                |
| doc                | quotes                  | BASE TABLE |                2 | 0                  |
| information_schema | character_sets          | BASE TABLE |             NULL | NULL               |
| information_schema | columns                 | BASE TABLE |             NULL | NULL               |
| information_schema | key_column_usage        | BASE TABLE |             NULL | NULL               |
| information_schema | referential_constraints | BASE TABLE |             NULL | NULL               |
| information_schema | routines                | BASE TABLE |             NULL | NULL               |
| information_schema | schemata                | BASE TABLE |             NULL | NULL               |
| information_schema | sql_features            | BASE TABLE |             NULL | NULL               |
| information_schema | table_constraints       | BASE TABLE |             NULL | NULL               |
| information_schema | table_partitions        | BASE TABLE |             NULL | NULL               |
| information_schema | tables                  | BASE TABLE |             NULL | NULL               |
| information_schema | views                   | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_am                   | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_attrdef              | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_attribute            | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_class                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_constraint           | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_database             | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_description          | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_enum                 | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_index                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_namespace            | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_proc                 | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_range                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_roles                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_settings             | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_stats                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_type                 | BASE TABLE |             NULL | NULL               |
| sys                | allocations             | BASE TABLE |             NULL | NULL               |
| sys                | checks                  | BASE TABLE |             NULL | NULL               |
| sys                | cluster                 | BASE TABLE |             NULL | NULL               |
| sys                | health                  | BASE TABLE |             NULL | NULL               |
| sys                | jobs                    | BASE TABLE |             NULL | NULL               |
| sys                | jobs_log                | BASE TABLE |             NULL | NULL               |
| sys                | jobs_metrics            | BASE TABLE |             NULL | NULL               |
| sys                | node_checks             | BASE TABLE |             NULL | NULL               |
| sys                | nodes                   | BASE TABLE |             NULL | NULL               |
| sys                | operations              | BASE TABLE |             NULL | NULL               |
| sys                | operations_log          | BASE TABLE |             NULL | NULL               |
| sys                | privileges              | BASE TABLE |             NULL | NULL               |
| sys                | repositories            | BASE TABLE |             NULL | NULL               |
| sys                | segments                | BASE TABLE |             NULL | NULL               |
| sys                | shards                  | BASE TABLE |             NULL | NULL               |
| sys                | snapshot_restore        | BASE TABLE |             NULL | NULL               |
| sys                | snapshots               | BASE TABLE |             NULL | NULL               |
| sys                | summits                 | BASE TABLE |             NULL | NULL               |
| sys                | users                   | BASE TABLE |             NULL | NULL               |
+--------------------+-------------------------+------------+------------------+--------------------+
SELECT 50 rows in set (... sec)

The table also contains additional information such as specified routing (Sharding) and partitioned by (Partitioned tables) columns:

cr> SELECT table_name, clustered_by, partitioned_by
... FROM information_schema.tables
... WHERE table_schema = 'doc'
... ORDER BY table_schema ASC, table_name ASC;
+-------------------+--------------+----------------+
| table_name        | clustered_by | partitioned_by |
+-------------------+--------------+----------------+
| galaxies          | NULL         | NULL           |
| locations         | id           | NULL           |
| partitioned_table | _id          | ["date"]       |
| quotes            | id           | NULL           |
+-------------------+--------------+----------------+
SELECT 4 rows in set (... sec)

Schema

Name Description Data Type
blobs_path The data path of the blob table TEXT
closed The state of the table BOOLEAN
clustered_by The routing column used to cluster the table TEXT
column_policy Defines whether the table uses a STRICT or a DYNAMIC Column policy TEXT
number_of_replicas The number of replicas the table currently has INTEGER
number_of_shards The number of shards the table is currently distributed across INTEGER
partitioned_by The column used to partition the table TEXT
reference_generation Specifies how values in the self-referencing column are generated TEXT
routing_hash_function The name of the hash function used for internal routing TEXT
self_referencing_column_name The name of the column that uniquely identifies each row (always _id) TEXT
settings WITH OBJECT
table_catalog Refers to the table_schema TEXT
table_name The name of the table TEXT
table_schema The name of the schema the table belongs to TEXT
table_type The type of the table (BASE TABLE for tables, VIEW for views) TEXT
version A collection of version numbers relevent to the table OBJECT

settings

Table settings specify configuration parameters for tables. Some settings can be set during Cluster runtime and others are only applied on cluster restart.

This list of table settings in WITH shows detailed information of each parameter.

Table parameters can be applied with CREATE TABLE on creation of a table. With ALTER TABLE they can be set on already existing tables.

The following statement creates a new table and sets the refresh interval of shards to 500 ms and sets the shard allocation for primary shards only:

cr> create table parameterized_table (id integer, content text)
... with ("refresh_interval"=500, "routing.allocation.enable"='primaries');
CREATE OK, 1 row affected (... sec)

The settings can be verified by querying information_schema.tables:

cr> select settings['routing']['allocation']['enable'] as alloc_enable,
...   settings['refresh_interval'] as refresh_interval
... from information_schema.tables
... where table_name='parameterized_table';
+--------------+------------------+
| alloc_enable | refresh_interval |
+--------------+------------------+
| primaries    |              500 |
+--------------+------------------+
SELECT 1 row in set (... sec)

On existing tables this needs to be done with ALTER TABLE statement:

cr> alter table parameterized_table
... set ("routing.allocation.enable"='none');
ALTER OK, -1 rows affected (... sec)

views

The table information_schema.views contains the name, definition and options of all available views.

cr> SELECT table_schema, table_name, view_definition
... FROM information_schema.views
... ORDER BY table_schema ASC, table_name ASC;
+--------------+------------+-------------------------+
| table_schema | table_name | view_definition         |
+--------------+------------+-------------------------+
| doc          | galaxies   | SELECT                  |
|              |            |   "id"                  |
|              |            | , "name"                |
|              |            | , "description"         |
|              |            | FROM "locations"        |
|              |            | WHERE "kind" = 'Galaxy' |
+--------------+------------+-------------------------+
SELECT 1 row in set (... sec)

Schema

Name Description Data Type
table_catalog The catalog of the table of the view (refers to table_schema) TEXT
table_schema The schema of the table of the view TEXT
table_name The name of the table of the view TEXT
view_definition The SELECT statement that defines the view TEXT
check_option Not applicable for CrateDB, always return NONE TEXT
is_updatable Whether the view is updatable. Not applicable for CrateDB, always returns FALSE BOOLEAN
owner The user that created the view TEXT

Note

If you drop the table of a view, the view will still exist and show up in the information_schema.tables and information_schema.views tables.

columns

This table can be queried to get a list of all available columns of all tables and views and their definition like data type and ordinal position inside the table:

cr> select table_name, column_name, ordinal_position as pos, data_type
... from information_schema.columns
... where table_schema = 'doc' and table_name not like 'my_table%'
... order by table_name asc, column_name asc;
+-------------------+--------------------------------+-----+--------------------------+
| table_name        | column_name                    | pos | data_type                |
+-------------------+--------------------------------+-----+--------------------------+
| locations         | date                           |   3 | timestamp with time zone |
| locations         | description                    |   6 | text                     |
| locations         | id                             |   1 | integer                  |
| locations         | information                    |  11 | object_array             |
| locations         | information['evolution_level'] |  12 | smallint                 |
| locations         | information['population']      |  13 | bigint                   |
| locations         | inhabitants                    |   7 | object                   |
| locations         | inhabitants['description']     |   8 | text                     |
| locations         | inhabitants['interests']       |   9 | text_array               |
| locations         | inhabitants['name']            |  10 | text                     |
| locations         | kind                           |   4 | text                     |
| locations         | landmarks                      |  14 | text_array               |
| locations         | name                           |   2 | text                     |
| locations         | position                       |   5 | integer                  |
| partitioned_table | date                           |   3 | timestamp with time zone |
| partitioned_table | id                             |   1 | bigint                   |
| partitioned_table | title                          |   2 | text                     |
| quotes            | id                             |   1 | integer                  |
| quotes            | quote                          |   2 | text                     |
+-------------------+--------------------------------+-----+--------------------------+
SELECT 19 rows in set (... sec)

You can even query this table’s own columns (attention: this might lead to infinite recursion of your mind, beware!):

cr> select column_name, data_type, ordinal_position
... from information_schema.columns
... where table_schema = 'information_schema'
... and table_name = 'columns' order by column_name asc;
+--------------------------+-----------+------------------+
| column_name              | data_type | ordinal_position |
+--------------------------+-----------+------------------+
| character_maximum_length | integer   |                1 |
| character_octet_length   | integer   |                2 |
| character_set_catalog    | text      |                3 |
| character_set_name       | text      |                4 |
| character_set_schema     | text      |                5 |
| check_action             | integer   |                6 |
| check_references         | text      |                7 |
| collation_catalog        | text      |                8 |
| collation_name           | text      |                9 |
| collation_schema         | text      |               10 |
| column_default           | text      |               11 |
| column_name              | text      |               12 |
| data_type                | text      |               13 |
| datetime_precision       | integer   |               14 |
| domain_catalog           | text      |               15 |
| domain_name              | text      |               16 |
| domain_schema            | text      |               17 |
| generation_expression    | text      |               18 |
| interval_precision       | integer   |               19 |
| interval_type            | text      |               20 |
| is_generated             | text      |               21 |
| is_nullable              | boolean   |               22 |
| numeric_precision        | integer   |               23 |
| numeric_precision_radix  | integer   |               24 |
| numeric_scale            | integer   |               25 |
| ordinal_position         | integer   |               26 |
| table_catalog            | text      |               27 |
| table_name               | text      |               28 |
| table_schema             | text      |               29 |
| udt_catalog              | text      |               30 |
| udt_name                 | text      |               31 |
| udt_schema               | text      |               32 |
+--------------------------+-----------+------------------+
SELECT 32 rows in set (... sec)

Schema

Name Description Data Type
table_catalog Refers to the table_schema TEXT
table_schema Schema name containing the table TEXT
table_name Table Name TEXT
column_name Column Name For fields in object columns this is not an identifier but a path and therefore must not be double quoted when programmatically obtained. TEXT
ordinal_position The position of the column within the table INTEGER
is_nullable Whether the column is nullable BOOLEAN
data_type

The data type of the column

For further information see Data types

 TEXT
column_default The default expression of the column TEXT
character_maximum_length If the data type is a character type then return the declared length limit; otherwise NULL. INTEGER
character_octet_length

Not implemented (always returns NULL)

Please refer to text type

 INTEGER
numeric_precision Indicates the number of significant digits for a numeric data_type. For all other data types this column is NULL. INTEGER
numeric_precision_radix Indicates in which base the value in the column numeric_precision for a numeric data_type is exposed. This can either be 2 (binary) or 10 (decimal). For all other data types this column is NULL. INTEGER
numeric_scale Not implemented (always returns NULL) INTEGER
datetime_precision Contains the fractional seconds precision for a timestamp data_type. For all other data types this column is null. INTEGER
interval_type Not implemented (always returns NULL) TEXT
interval_precision Not implemented (always returns NULL) INTEGER
character_set_catalog Not implemented (always returns NULL) TEXT
character_set_schema Not implemented (always returns NULL) TEXT
character_set_name Not implemented (always returns NULL) TEXT
collation_catalog Not implemented (always returns NULL) TEXT
collation_schema Not implemented (always returns NULL) TEXT
collation_name Not implemented (always returns NULL) TEXT
domain_catalog Not implemented (always returns NULL) TEXT
domain_schema Not implemented (always returns NULL) TEXT
domain_name Not implemented (always returns NULL) TEXT
udt_catalog Not implemented (always returns NULL) TEXT
udt_schema Not implemented (always returns NULL) TEXT
udt_name Not implemented (always returns NULL) TEXT
check_references Not implemented (always returns NULL) TEXT
check_action Not implemented (always returns NULL) INTEGER
generation_expression The expression used to generate ad column. If the column is not generated NULL is returned. TEXT
is_generated Returns ALWAYS or NEVER wether the column is generated or not. TEXT

table_constraints

This table can be queried to get a list of all defined table constraints, their type, name and which table they are defined in.

Note

Currently only PRIMARY_KEY constraints are supported.

cr> select table_schema, table_name, constraint_name, constraint_type as type
... from information_schema.table_constraints
... where table_name = 'tables'
...   or table_name = 'quotes'
...   or table_name = 'documents'
...   or table_name = 'tbl'
... order by table_schema desc, table_name asc limit 10;
+--------------------+------------+-...------------------+-------------+
| table_schema       | table_name | constraint_name      | type        |
+--------------------+------------+-...------------------+-------------+
| information_schema | tables     | tables_pk            | PRIMARY KEY |
| doc                | quotes     | quotes_pk            | PRIMARY KEY |
| doc                | tbl        | doc_tbl_col_not_null | CHECK       |
+--------------------+------------+-...------------------+-------------+
SELECT 3 rows in set (... sec)

key_column_usage

This table may be queried to retrieve primary key information from all user tables:

cr> select constraint_name, table_name, column_name, ordinal_position
... from information_schema.key_column_usage
... where table_name = 'students'
+-----------------+------------+-------------+------------------+
| constraint_name | table_name | column_name | ordinal_position |
+-----------------+------------+-------------+------------------+
| students_pk     | students   | id          |                1 |
| students_pk     | students   | department  |                2 |
+-----------------+------------+-------------+------------------+
SELECT 2 rows in set (... sec)

Schema

Name Description Data Type
constraint_catalog Refers to table_catalog TEXT
constraint_schema Refers to table_schema TEXT
constraint_name Name of the constraint TEXT
table_catalog Refers to table_schema TEXT
table_schema Name of the schema that contains the table that contains the constraint TEXT
table_name Name of the table that contains the constraint TEXT
column_name Name of the column that contains the constraint TEXT
ordinal_position Position of the column within the contraint (starts with 1) INTEGER

table_partitions

This table can be queried to get information about all partitioned tables, Each partition of a table is represented as one row. The row contains the information table name, schema name, partition ident, and the values of the partition. values is a key-value object with the ‘partitioned by column’ as key(s) and the corresponding value as value(s).

For further information see Partitioned tables.

cr> insert into a_partitioned_table (id, content) values (1, 'content_a');
INSERT OK, 1 row affected (... sec)

cr> alter table a_partitioned_table set (number_of_shards=5);
ALTER OK, -1 rows affected (... sec)

cr> insert into a_partitioned_table (id, content) values (2, 'content_b');
INSERT OK, 1 row affected (... sec)

The following example shows a table where the column ‘content’ of table ‘a_partitioned_table’ has been used to partition the table. The table has two partitions. The partitions are introduced when data is inserted where ‘content’ is ‘content_a’, and ‘content_b’.:

cr> select table_name, table_schema as schema, partition_ident, "values"
... from information_schema.table_partitions
... order by table_name, partition_ident;
+---------------------+--------+--------------------+--------------------------+
| table_name          | schema | partition_ident    | values                   |
+---------------------+--------+--------------------+--------------------------+
| a_partitioned_table | doc    | 04566rreehimst2vc4 | {"content": "content_a"} |
| a_partitioned_table | doc    | 04566rreehimst2vc8 | {"content": "content_b"} |
+---------------------+--------+--------------------+--------------------------+
SELECT 2 rows in set (... sec)

The second partition has been created after the number of shards for future partitions have been changed on the partitioned table, so they show 5 instead of 4:

cr> select table_name, partition_ident,
... number_of_shards, number_of_replicas
... from information_schema.table_partitions
... order by table_name, partition_ident;
+---------------------+--------------------+------------------+--------------------+
| table_name          | partition_ident    | number_of_shards | number_of_replicas |
+---------------------+--------------------+------------------+--------------------+
| a_partitioned_table | 04566rreehimst2vc4 |                4 | 0-1                |
| a_partitioned_table | 04566rreehimst2vc8 |                5 | 0-1                |
+---------------------+--------------------+------------------+--------------------+
SELECT 2 rows in set (... sec)

routines

The routines table contains tokenizers, token-filters, char-filters, custom analyzers created by CREATE ANALYZER statements (see Creating a custom analyzer), and functions created by CREATE FUNCTION statements:

cr> select routine_name, routine_type
... from information_schema.routines
... group by routine_name, routine_type
... order by routine_name asc limit 5;
+----------------------+--------------+
| routine_name         | routine_type |
+----------------------+--------------+
| PathHierarchy        | TOKENIZER    |
| apostrophe           | TOKEN_FILTER |
| arabic               | ANALYZER     |
| arabic_normalization | TOKEN_FILTER |
| arabic_stem          | TOKEN_FILTER |
+----------------------+--------------+
SELECT 5 rows in set (... sec)

For example you can use this table to list existing tokenizers like this:

cr> select routine_name
... from information_schema.routines
... where routine_type='TOKENIZER'
... order by routine_name asc limit 10;
+----------------+
| routine_name   |
+----------------+
| PathHierarchy  |
| char_group     |
| classic        |
| edge_ngram     |
| keyword        |
| letter         |
| lowercase      |
| ngram          |
| path_hierarchy |
| pattern        |
+----------------+
SELECT 10 rows in set (... sec)

Or get an overview of how many routines and routine types are available:

cr> select count(*), routine_type
... from information_schema.routines
... group by routine_type
... order by routine_type;
+----------+--------------+
| count(*) | routine_type |
+----------+--------------+
|       45 | ANALYZER     |
|        3 | CHAR_FILTER  |
|       16 | TOKENIZER    |
|       62 | TOKEN_FILTER |
+----------+--------------+
SELECT 4 rows in set (... sec)

Schema

Name Data Type
routine_name TEXT
routine_type TEXT
routine_body TEXT
routine_schema TEXT
data_type TEXT
is_deterministic BOOLEAN
routine_definition TEXT
specific_name TEXT
routine_name:Name of the routine (might be duplicated in case of overloading)
routine_type:Type of the routine. Can be FUNCTION, ANALYZER, CHAR_FILTER, TOKEN_FILTER or TOKEN_FILTER.
routine_schema:The schema where the routine was defined. If it doesn’t apply, then NULL.
routine_body:The language used for the routine implementation. If it doesn’t apply, then NULL.
data_type:The return type of the function. If it doesn’t apply, then NULL.
is_deterministic:If the routine is deterministic then True, else False (NULL if it doesn’t apply).
routine_definition:The function definition (NULL if it doesn’t apply).
specific_name:Used to uniquely identify the function in a schema, even if the function is overloaded. Currently the specific name contains the types of the function arguments. As the format might change in the future, it should be only used to compare it to other instances of specific_name.

schemata

The schemata table lists all existing schemas. Thes blob, information_schema, and sys schemas are always available. The doc schema is available after the first user table is created.

cr> select schema_name from information_schema.schemata order by schema_name;
+--------------------+
| schema_name        |
+--------------------+
| blob               |
| doc                |
| information_schema |
| pg_catalog         |
| sys                |
+--------------------+
SELECT 5 rows in set (... sec)

sql_features

The sql_features table outlines supported and unsupported SQL features of CrateDB based to the current SQL standard (see SQL standard compliance):

cr> select feature_name, is_supported, sub_feature_id, sub_feature_name
... from information_schema.sql_features
... where feature_id='F501';
+--------------------------------+--------------+----------------+--------------------+
| feature_name                   | is_supported | sub_feature_id | sub_feature_name   |
+--------------------------------+--------------+----------------+--------------------+
| Features and conformance views | FALSE        |                |                    |
| Features and conformance views | TRUE         | 1              | SQL_FEATURES view  |
| Features and conformance views | FALSE        | 2              | SQL_SIZING view    |
| Features and conformance views | FALSE        | 3              | SQL_LANGUAGES view |
+--------------------------------+--------------+----------------+--------------------+
SELECT 4 rows in set (... sec)
Name Data Type Nullable
feature_id TEXT NO
feature_name TEXT NO
sub_feature_id TEXT NO
sub_feature_name TEXT NO
is_supported TEXT NO
is_verified_by TEXT YES
comments TEXT YES
feature_id:

Identifier of the feature
feature_name:

Descriptive name of the feature by the Standard
sub_feature_id:

Identifier of the subfeature; If it has zero-length, this is a feature
sub_feature_name:

Descriptive name of the subfeature by the Standard; If it has zero-length, this is a feature
is_supported:

YES if the feature is fully supported by the current version of CrateDB, NO if not
is_verified_by:

Identifies the conformance test used to verify the claim;

Always NULL since the CrateDB development group does not perform formal testing of feature conformance
comments:

Either NULL or shows a comment about the supported status of the feature

character_sets

The character_sets table identifies the character sets available in the current database.

In CrateDB there is always a single entry listing UTF8:

cr> SELECT character_set_name, character_repertoire FROM information_schema.character_sets;
+--------------------+----------------------+
| character_set_name | character_repertoire |
+--------------------+----------------------+
| UTF8               | UCS                  |
+--------------------+----------------------+
SELECT 1 row in set (... sec)
Column Name Return Type Description
character_set_catalog TEXT Not implemented, this column is always null.
character_set_schema TEXT Not implemented, this column is always null.
character_set_name TEXT Name of the character set
character_repertoire TEXT Character repertoire
form_of_use TEXT Character encoding form, same as character_set_name
default_collate_catalog TEXT Name of the database containing the default collation (Always crate)
default_collate_schema TEXT Name of the schema containing the default collation (Always NULL)
default_collate_name TEXT Name of the default collation (Always NULL)

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