homework-jianmu/docs/en/12-taos-sql/22-meta.md

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Metadata	Information_Schema Database

TDengine includes a built-in database named INFORMATION_SCHEMA to provide access to database metadata, system information, and status information. This information includes database names, table names, and currently running SQL statements. All information related to TDengine maintenance is stored in this database. It contains several read-only tables. These tables are more accurately described as views, and they do not correspond to specific files. You can query these tables but cannot write data to them. The INFORMATION_SCHEMA database is intended to provide a unified method for SHOW commands to access data. However, using SELECT ... FROM INFORMATION_SCHEMA.tablename offers several advantages over SHOW commands:

1. You can use a USE statement to specify the INFORMATION_SCHEMA database as the current database.
2. You can use the familiar SELECT syntax to access information, provided that you know the table and column names.
3. You can filter and order the query results. More generally, you can use any SELECT syntax that TDengine supports to query the INFORMATION_SCHEMA database.
4. Future versions of TDengine can add new columns to INFORMATION_SCHEMA tables without affecting existing business systems.
5. It is easier for users coming from other database management systems. For example, Oracle users can query data dictionary tables.

:::info

• SHOW statements are still supported for the convenience of existing users.
• Some columns in the system table may be keywords, and you need to use the escape character '`' when querying, for example, to query the VGROUPS in the database test:

   select `vgroups` from ins_databases where name = 'test';

:::

This document introduces the tables of INFORMATION_SCHEMA and their structure.

INS_DNODES

Provides information about dnodes. Similar to SHOW DNODES.

#	Column	Data Type	Description
1	vnodes	SMALLINT	Current number of vnodes on the dnode
2	vnodes	SMALLINT	Maximum number of vnodes on the dnode
3	status	BINARY(10)	Current status
4	note	BINARY(256)	Reason for going offline or other information
5	id	SMALLINT	Dnode ID
6	endpoint	BINARY(134)	Dnode endpoint
7	create	TIMESTAMP	Creation time

INS_MNODES

Provides information about mnodes. Similar to SHOW MNODES.

#	Column	Data Type	Description
1	id	SMALLINT	Mnode ID
2	endpoint	BINARY(134)	Mnode endpoint
3	role	BINARY(10)	Current role
4	role_time	TIMESTAMP	Time at which the current role was assumed
5	create_time	TIMESTAMP	Creation time

INS_MODULES

Provides information about modules. Similar to SHOW MODULES.

#	Column	Data Type	Description
1	id	SMALLINT	Module ID
2	endpoint	BINARY(134)	Module endpoint
3	module	BINARY(10)	Module status

INS_QNODES

Provides information about qnodes. Similar to SHOW QNODES.

#	Column	Data Type	Description
1	id	SMALLINT	Qnode ID
2	endpoint	BINARY(134)	Qnode endpoint
3	create_time	TIMESTAMP	Creation time

INS_CLUSTER

Provides information about the cluster.

#	Column	Data Type	Description
1	id	BIGINT	Cluster ID
2	name	BINARY(134)	Cluster name
3	create_time	TIMESTAMP	Creation time

INS_DATABASES

Provides information about user-created databases. Similar to SHOW DATABASES.

#	Column	Data Type	Description
1	name	BINARY(32)	Database name
2	create_time	TIMESTAMP	Creation time
3	ntables	INT	Number of standard tables and subtables (not including supertables)
4	vgroups	INT	Number of vgroups
6	replica	INT	Number of replicas
7	quorum	BINARY(3)	Strong consistency
8	duration	INT	Duration for storage of single files
9	keep	INT	Data retention period
10	buffer	INT	Write cache size per vnode, in MB
11	pagesize	INT	Page size for vnode metadata storage engine, in KB
12	pages	INT	Number of pages per vnode metadata storage engine
13	minrows	INT	Maximum number of records per file block
14	maxrows	INT	Minimum number of records per file block
15	comp	INT	Compression method
16	precision	BINARY(2)	Time precision
17	status	BINARY(10)	Current database status
18	retention	BINARY (60)	Aggregation interval and retention period
19	single_stable	BOOL	Whether the database can contain multiple supertables
20	cachemodel	BINARY(60)	Caching method for the newest data
21	cachesize	INT	Memory per vnode used for caching the newest data
22	wal_level	INT	WAL level
23	wal_fsync_period	INT	Interval at which WAL is written to disk
24	wal_retention_period	INT	WAL retention period
25	wal_retention_size	INT	Maximum WAL size
26	wal_roll_period	INT	WAL rotation period
27	wal_segment_size	BIGINT	WAL file size
28	stt_trigger	SMALLINT	The threshold for number of files to trigger file merging
29	table_prefix	SMALLINT	The prefix length in the table name that is ignored when distributing table to vnode based on table name
30	table_suffix	SMALLINT	The suffix length in the table name that is ignored when distributing table to vnode based on table name
31	tsdb_pagesize	INT	The page size for internal storage engine, its unit is KB

INS_FUNCTIONS

Provides information about user-defined functions.

#	Column	Data Type	Description
1	name	BINARY(64)	Function name
2	comment	BINARY(255)	Function description
3	aggregate	INT	Whether the UDF is an aggregate function
4	output_type	BINARY(31)	Output data type
5	create_time	TIMESTAMP	Creation time
6	code_len	INT	Length of the source code
7	bufsize	INT	Buffer size

INS_INDEXES

Provides information about user-created indices. Similar to SHOW INDEX.

#	Column	Data Type	Description
1	db_name	BINARY(32)	Database containing the table with the specified index
2	table_name	BINARY(192)	Table containing the specified index
3	index_name	BINARY(192)	Index name
4	db_name	BINARY(64)	Index column
5	index_type	BINARY(10)	SMA or FULLTEXT index
6	index_extensions	BINARY(256)	Other information For SMA indices, this shows a list of functions. For FULLTEXT indices, this is null.

INS_STABLES

Provides information about supertables.

#	Column	Data Type	Description
1	stable_name	BINARY(192)	Supertable name
2	db_name	BINARY(64)	All databases in the supertable
3	create_time	TIMESTAMP	Creation time
4	columns	INT	Number of columns
5	tags	INT	Number of tags
6	last_update	TIMESTAMP	Last updated time
7	table_comment	BINARY(1024)	Table description
8	watermark	BINARY(64)	Window closing time
9	max_delay	BINARY(64)	Maximum delay for pushing stream processing results
10	rollup	BINARY(128)	Rollup aggregate function

INS_TABLES

Provides information about standard tables and subtables.

#	Column	Data Type	Description
1	table_name	BINARY(192)	Table name
2	db_name	BINARY(64)	Database name
3	create_time	TIMESTAMP	Creation time
4	columns	INT	Number of columns
5	stable_name	BINARY(192)	Supertable name
6	uid	BIGINT	Table ID
7	vgroup_id	INT	Vgroup ID
8	ttl	INT	Table time-to-live
9	table_comment	BINARY(1024)	Table description
10	type	BINARY(20)	Table type

INS_TAGS

#	Column	Data Type	Description
1	table_name	BINARY(192)	Table name
2	db_name	BINARY(64)	Database name
3	stable_name	BINARY(192)	Supertable name
4	tag_name	BINARY(64)	Tag name
5	tag_type	BINARY(64)	Tag type
6	tag_value	BINARY(16384)	Tag value

INS_USERS

Provides information about TDengine users.

#	Column	Data Type	Description
1	user_name	BINARY(23)	User name
2	privilege	BINARY(256)	User permissions
3	create_time	TIMESTAMP	Creation time

INS_GRANTS

Provides information about TDengine Enterprise Edition permissions.

#	Column	Data Type	Description
1	version	BINARY(9)	Whether the deployment is a licensed or trial version
2	cpu_cores	BINARY(9)	CPU cores included in license
3	dnodes	BINARY(10)	Dnodes included in license
4	streams	BINARY(10)	Streams included in license
5	users	BINARY(10)	Users included in license
6	streams	BINARY(10)	Accounts included in license
7	storage	BINARY(21)	Storage space included in license
8	connections	BINARY(21)	Client connections included in license
9	databases	BINARY(11)	Databases included in license
10	speed	BINARY(9)	Write speed specified in license (data points per second)
11	querytime	BINARY(9)	Total query time specified in license
12	timeseries	BINARY(21)	Number of metrics included in license
13	expired	BINARY(5)	Whether the license has expired
14	expire_time	BINARY(19)	When the trial period expires

INS_VGROUPS

Provides information about vgroups.

#	Column	Data Type	Description
1	vgroup_id	INT	Vgroup ID
2	db_name	BINARY(32)	Database name
3	tables	INT	Tables in vgroup
4	status	BINARY(10)	Vgroup status
5	v1_dnode	INT	Dnode ID of first vgroup member
6	v1_status	BINARY(10)	Status of first vgroup member
7	v2_dnode	INT	Dnode ID of second vgroup member
8	v2_status	BINARY(10)	Status of second vgroup member
9	v3_dnode	INT	Dnode ID of third vgroup member
10	v3_status	BINARY(10)	Status of third vgroup member
11	nfiles	INT	Number of data and metadata files in the vgroup
12	file_size	INT	Size of the data and metadata files in the vgroup
13	tsma	TINYINT	Whether time-range-wise SMA is enabled. 1 means enabled; 0 means disabled.

INS_CONFIGS

Provides system configuration information.

#	Column	Data Type	Description
1	name	BINARY(32)	Parameter
2	value	BINARY(64)	Value

INS_DNODE_VARIABLES

Provides dnode configuration information.

#	Column	Data Type	Description
1	dnode_id	INT	Dnode ID
2	name	BINARY(32)	Parameter
3	value	BINARY(64)	Value

INS_TOPICS

#	Column	Data Type	Description
1	topic_name	BINARY(192)	Topic name
2	db_name	BINARY(64)	Database for the topic
3	create_time	TIMESTAMP	Creation time
4	sql	BINARY(1024)	SQL statement used to create the topic

INS_SUBSCRIPTIONS

#	Column	Data Type	Description
1	topic_name	BINARY(204)	Subscribed topic
2	consumer_group	BINARY(193)	Subscribed consumer group
3	vgroup_id	INT	Vgroup ID for the consumer
4	consumer_id	BIGINT	Consumer ID

INS_STREAMS

#	Column	Data Type	Description
1	stream_name	BINARY(64)	Stream name
2	create_time	TIMESTAMP	Creation time
3	sql	BINARY(1024)	SQL statement used to create the stream
4	status	BIANRY(20)	Current status
5	source_db	BINARY(64)	Source database
6	target_db	BIANRY(64)	Target database
7	target_table	BINARY(192)	Target table
8	watermark	BIGINT	Watermark (see stream processing documentation)
9	trigger	INT	Method of triggering the result push (see stream processing documentation)