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SNAPSHOT

Updated on 2024-05-07 GMT+08:00

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 separation of duties (enableSeparationOfDuty is set to ON) scenarios.
  • When you need a stable and available snapshot for tasks such as AI training, you need to publish the snapshot.

Syntax

  1. 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]]
          [COMMENT IS comment_item]
          AS query;
    • CREATE SNAPSHOT FROM
      CREATE SNAPSHOT qualified_name [@ [version]]
          FROM @ version
          [COMMENT IS comment_item]
              USING (
              { INSERT [INTO SNAPSHOT] insert_item
                | UPDATE [SNAPSHOT] [AS alias] SET set_item [FROM from_item] [WHERE where_item]
                | DELETE [FROM SNAPSHOT] [AS alias] [USING using_item] [WHERE where_item]
                | ALTER [SNAPSHOT] { ADD and_item | DROP drop_item } [, ...]
            } [; ...]
          );
  2. Delete a snapshot.
    PURGE SNAPSHOT
    PURGE SNAPSHOT qualified_name @ version;
  3. Sample snapshots.
    SAMPLE SNAPSHOT
    SAMPLE SNAPSHOT qualified_name @ version
        [STRATIFY BY attr_list]
        { AS alias AT RATIO num [COMMENT IS comment_item] } [, ...]
  4. Publish snapshots.
    PUBLISH SNAPSHOT
    PUBLISH SNAPSHOT qualified_name @ version;
  5. Archive snapshots.
    ARCHIVE SNAPSHOT
    ARCHIVE SNAPSHOT qualified_name @ version;
  6. Query snapshots.
    SELECT * FROM DB4AISHOT (qualified_name @ version );

Parameters

  • qualified_name

    Name of the snapshot to be created

    Value range: a string. It must comply with the naming convention.

  • 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.

  • comment_item

    Specifies the comment to be added.

    Value range: a string. It must comply with the naming convention.

  • insert_item

    Specifies the name of the object to be inserted.

    Value range: a string. It must comply with the naming convention.

  • alias

    Specifies the alias of the current object.

    Value range: a string. It must comply with the naming convention.

  • set_item

    Specifies the name of the object on which the operation is performed.

    Value range: a string. It must comply with the naming convention.

  • from_item

    Specifies the name of the query source object connected.

    Value range: a string. It must comply with the naming convention.

  • where_item

    The return value is any expression of the Boolean type.

    Value range: a string. It must comply with the naming convention.

  • using_item

    Specifies the name of the object used for connection.

    Value range: a string. It must comply with the naming convention.

  • and_item

    Specifies the name of the object to be processed in parallel.

    Value range: a string. It must comply with the naming convention.

  • drop_item

    Specifies the name of the object to be dropped.

    Value range: a string. It must comply with the naming convention.

  • attr_list

    Specifies the list of target objects.

    Value range: a string. It must comply with the naming convention.

  • num

    Specifies the ratio.

    Its value is a digit.

Examples

-- Create a data table.
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);

-- 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;

-- Delete the table.
gaussdb=# DROP TABLE t1;

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