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 separation of duty (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;