SNAPSHOT
Description
Controls data in a unified manner for multiple users.
Precautions
- The GUC parameter db4ai_snapshot_mode classifies the snapshot storage models into MSS and CSS. The GUC parameter db4ai_snapshot_version_delimiter specifies the version separator and its default value is @. The GUC parameter db4ai_snapshot_version_separator specifies the sub-version separator and its default value is ..
- When the incremental storage mode is used for snapshots, the snapshots are dependent on each other. Snapshots must be deleted in the dependency sequence.
- The snapshot feature is used to maintain data between team members, involving data transcription between administrators and common users. Therefore, the snapshot feature is not supported in the separation-of-duties scenario (enableSeparationOfDuty is set to ON).
- When you need a stable and available snapshot for tasks such as AI training, you need to publish the snapshot.
Syntax
- Create a snapshot.
You can use the CREATE SNAPSHOT... AS and CREATE SNAPSHOT... FROM statements to create a data table snapshot.
- CREATE SNAPSHOT AS
CREATE SNAPSHOT <qualified_name> [@ <version | ident | sconst>] [COMMENT IS <sconst>} AS query;
- CREATE SNAPSHOT FROM
CREATE SNAPSHOT <qualified_name> [@ <version | ident | sconst>] FROM @ <version | ident | sconst> [COMMENT IS <comment>} USING ( { INSERT [INTO SNAPSHOT] ... | UPDATE [SNAPSHOT] [AS <alias>] SET ... [FROM ...] [WHERE ...] | DELETE [FROM SNAPSHOT] [AS <alias>] [USING ...] [WHERE ...] | ALTER [SNAPSHOT] { ADD ... | DROP ... } [, ...] } [; …] );
- CREATE SNAPSHOT AS
- Delete a snapshot.
- Sample snapshots.
- Publish snapshots.
- Archive snapshots.
- Query snapshots.
SELECT * FROM DB4AISHOT(<qualified_name> @ <version | ident | sconst> );
Parameters
- qualified_name
Name of the snapshot to be created
Value range: a string that complies with the Identifier Naming Conventions.
- version
(Optional) Version number of a snapshot. This parameter is optional. The system automatically extends the sequence number.
Value range: string, consisting of numbers and separators.
- ident
Identifies the snapshot suffix number (or major version).
Value range: an integer.
- sconst
Marks the version number with a floating-point number. The feature replaces the decimal point with the separator specified by the GUC parameter db4ai_snapshot_version_separator in the background.
Value range: a floating-point number.
- comment
Specifies the comment to be added.
Value range: a string that complies with the Identifier Naming Conventions.
- alias
Specifies the alias of the current object.
Value range: a string that complies with the Identifier Naming Conventions.
- attr_list
Specifies the list of target objects.
Value range: a string that complies with the Identifier Naming Conventions.
- label
Alias of the sampled data column.
Value range: a string that complies with the Identifier Naming Conventions.
- num
Specifies the ratio.
Its value is a digit.
Examples
-- Create data table t1. gaussdb=# CREATE TABLE t1 (id int, name varchar); -- Insert data. gaussdb=# INSERT INTO t1 VALUES (1, 'zhangsan'); gaussdb=# INSERT INTO t1 VALUES (2, 'lisi'); gaussdb=# INSERT INTO t1 VALUES (3, 'wangwu'); gaussdb=# INSERT INTO t1 VALUES (4, 'lisa'); gaussdb=# INSERT INTO t1 VALUES (5, 'jack'); -- Create a snapshot. gaussdb=# CREATE SNAPSHOT s1@1.0 comment is 'first version' AS SELECT * FROM t1; -- Create snapshots in iteration mode. gaussdb=# CREATE SNAPSHOT s1@2.0 FROM @1.0 comment is 'inherits from @1.0' USING (INSERT VALUES(6, 'john'), (7, 'tim'); DELETE WHERE id = 1); -- View snapshot content. gaussdb=# SELECT * FROM DB4AISHOT(s1@1.0); id | name ----+---------- 1 | zhangsan 2 | lisi 3 | wangwu 4 | lisa 5 | jack (5 rows) gaussdb=# SELECT * FROM DB4AISHOT(s1@2.0); id | name ----+-------- 2 | lisi 3 | wangwu 4 | lisa 5 | jack 6 | john 7 | tim (6 rows) -- Sample snapshots. gaussdb=# SAMPLE SNAPSHOT s1@2.0 stratify by name as nick at ratio .5; -- Delete snapshots. gaussdb=# PURGE SNAPSHOT s1@2.0; gaussdb=# PURGE SNAPSHOT s1nick@2.0; gaussdb=# PURGE SNAPSHOT s1@1.0; -- Drop table t1. gaussdb=# DROP TABLE t1;
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