Overview

Global sequences are mainly database-based global sequences.

Note

The start auto-increment SN can be modified.
Global sequence provides sequence numbers that are globally unique but may not increase continuously.
If the auto-increment sequence is used, its value must be null. If you do not specify the value or set it to null, DDM will assign a value by default. The user-defined value may conflict with the assigned auto-increment key value.

Table 1 Table types supported by global sequence
Table Type	Sharded	Broadcast	Unsharded
DB-based	Supported	Supported	Not supported

Connect to a DDM instance.
Open the required schema.
Run the following command to create an auto-increment sequence:
create sequence <sequence name >
Note
The auto-increment key should be a BIGINT value. To avoid duplicate values, do not use TINYINT, SMALLINT, MEDIUMINT, INTEGER, or INT as the auto-increment key.
Run show sequences to view the usage of the auto-increment sequence. If the usage reaches 100%, do not insert data any more and contact DDM technical support.

Connect to a DDM instance.
Open the required schema.
Run show sequences to view all global sequences.
Run the command to change the start value:
alter sequence <sequence name > START WITH <start value of the target sequence >

Notice

This feature is only available in kernel 3.0.3 and later versions.

Connect to a DDM instance.
Log in to the required schema.
Run the following command to change cached values of the global sequence of table test:
alter sequence test cache 5000
Run the following command to view cached values (or INCREMENT values) of the global sequence of table test:
show sequences

Notice

This feature is available only in kernel 3.0.4.1 or later.

Connect to a DDM instance.
Run the following command to change sequences of all schemas:
fresh all sequence start value

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