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Help Center/ GaussDB/ Feature Guide(Centralized_V2.0-8.x)/ Storage Engine/ Data Lifecycle Management: OLTP Table Compression/ Usage Guide

Usage Guide

Updated on 2024-06-07 GMT+08:00

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To use the advanced compression function, you must purchase a license. For details, contact Huawei technical support.

Run the following command to enable the compression function:

gaussdb=# ALTER DATABASE SET ilm = on;

Check whether gsilmpolicy_seq and gsilmtask_seq exist in the public schema of the current database.

gaussdb=# \d
                                            List of relations
 Schema |      Name       |   Type   |   Owner    |                       Storage                        
--------+-----------------+----------+------------+------------------------------------------------------
 public | gsilmpolicy_seq | sequence | omm |
 | 
 public | gsilmtask_seq   | sequence | omm |
 |

gaussdb=# SELECT a.oid, a.relname from pg_class a inner join pg_namespace b on a.relnamespace = b.oid
    WHERE (a.relname = 'gsilmpolicy_seq' OR a.relname = 'gsilmtask_seq') AND b.nspname = 'public';

  oid  |     relname     
-------+-----------------
 17002 | gsilmpolicy_seq
 17004 | gsilmtask_seq
(2 rows)

If an exception occurs, a warning is reported.

WARNING:  ILM sequences are already existed while initializing

Add a compression policy for a table.

Create a table with a policy.

gaussdb=# CREATE TABLE ilm_table_1 (col1 int, col2 text)
    ilm add policy row store compress advanced row
    after 3 days of no modification on (col1 < 1000);

Add a policy for an existing table.

gaussdb=# CREATE TABLE ilm_table_2 (col1 int, col2 text);
gaussdb=# ALTER TABLE ilm_table_2 ilm add policy row store
    compress advanced row after 3 days of no modification;

Check whether data is added to the policy view.

gaussdb=# SELECT * FROM gs_my_ilmpolicies;

 policy_name |  policy_type  | tablespace | enabled | deleted 
-------------+---------------+------------+---------+---------
 p1          | DATA MOVEMENT |            | YES     | NO
 p2          | DATA MOVEMENT |            | YES     | NO
(2 rows)

Check whether the policy that meets the settings is added to the policy details view.

gaussdb=# SELECT * FROM gs_my_ilmdatamovementpolicies;

 policy_name | action_type | scope | compression_level | tier_tablespace | tier_status |     condition_type     | condition_days | custom_function | policy_subtype | action_clause | tier_to 
-------------+-------------+-------+-------------------+-----------------+-------------+------------------------+----------------+-----------------+----------------+---------------+---------
 p1          | COMPRESSION | ROW   | ADVANCED          |                 |             | LAST MODIFICATION TIME |              3 |                 |                |               | 
 p2          | COMPRESSION | ROW   | ADVANCED          |                 |             | LAST MODIFICATION TIME |              3 |                 |                |               | 
(2 rows)

Check whether the policy corresponds to the target table.

gaussdb=# SELECT * FROM gs_my_ilmobjects;
 policy_name | object_owner | object_name | subobject_name | object_type |    inherited_from    | tbs_inherited_from | enabled | deleted 
-------------+--------------+-------------+----------------+-------------+----------------------+--------------------+---------+---------
 p1          | public       | ilm_table_1 |                | TABLE       | POLICY NOT INHERITED |                    | YES     | NO
 p2          | public       | ilm_table_2 |                | TABLE       | POLICY NOT INHERITED |                    | YES     | NO
(2 rows)

Perform compression evaluation.

Manually perform compression evaluation.

CAUTION:

To facilitate the test, the POLICY_TIME attribute is provided in the environment parameters of this function to determine whether the time unit is day or second. Run the following statement:

gaussdb=# CALL DBE_ILM_ADMIN.CUSTOMIZE_ILM(11, 1);

Insert random data for testing:

gaussdb=# INSERT INTO ilm_table_1 select *, 'test_data' FROM generate_series(1, 10000);

gaussdb=# DECLARE
    v_taskid number;
gaussdb=# BEGIN
    DBE_ILM.EXECUTE_ILM(OWNER           => 'public',
                        OBJECT_NAME     => 'ilm_table_1',
                        TASK_ID         => v_taskid,
                        SUBOBJECT_NAME  => NULL,
                        POLICY_NAME     => 'ALL POLICIES',
                        EXECUTION_MODE  => 2);
    RAISE INFO 'Task ID is:%', v_taskid;
gaussdb=# END;
/

If the input parameter is incorrect, an error message is displayed. If no error occurs, no information is displayed. (The RAISE INFO statement is added to the preceding code segment to print the ID of the current task.)

INFO:  Task ID is:1

Check the task information.

gaussdb=# SELECT * FROM gs_my_ilmtasks;

task_id | task_owner |   state   |         creation_time         |          start_time           |        completion_time        
---------+------------+-----------+-------------------------------+-------------------------------+-------------------------------
       1 | omm | COMPLETED | 2023-08-29 17:36:38.779555+08 | 2023-08-29 17:36:38.779555+08 | 2023-08-29 17:36:38.879485+08
(1 row)

Check the evaluation result.

gaussdb=# SELECT * FROM gs_my_ilmevaluationdetails;

 task_id | policy_name | object_owner | object_name | subobject_name | object_type | selected_for_execution |      job_name     | comments 
---------+-------------+--------------+-------------+----------------+-------------+------------------------+-------------------+----------
       1 | p1          | public       | ilm_table_1 |                | TABLE       | SELECTED FOR EXECUTION | ilmjob$_postgres1 | 
(1 row)

Check the compression job information.

gaussdb=# SELECT * FROM gs_my_ilmresults;

 task_id |     job_name      |       job_state        |          start_time           |        completion_time        | comments |               statistics               
---------+-------------------+------------------------+-------------------------------+-------------------------------+----------+----------------------------------------
       1 | ilmjob$_postgres1 | COMPLETED SUCCESSFULLY | 2023-08-29 17:36:38.779555+08 | 2023-08-29 17:36:38.879485+08 |          | SpaceSaving=0,BoundTime=0,LastBlkNum=0
(1 row)

Trigger automatic scheduling evaluation in the background.

gaussdb=# 
DECLARE
    V_HOUR INT := 22;
    V_MINUTE INT := 0;
    V_SECOND INT := 0;
    C_ADO_WINDOW_SCHEDULE_NAME TEXT := 'ado_window_schedule';
    C_ADO_WINDOW_PROGRAM_NAME TEXT := 'ado_window_program';
    C_MAINTENANCE_WINDOW_JOB_NAME TEXT := 'maintenance_window_job';
    V_MAINTENCE_WINDOW_REPEAT TEXT;
    V_MAINTENCE_WINDOW_START TIMESTAMPTZ;
    V_BE_SCHEDULE_ENABLE BOOL;
    V_MAINTENANCE_WINDOW_EXIST INT;
BEGIN
    SELECT COUNT(*) INTO V_MAINTENANCE_WINDOW_EXIST FROM PG_CATALOG.PG_JOB WHERE JOB_NAME = 'maintenance_window_job' AND DBNAME = 'template1';
    IF CURRENT_DATABASE() != 'template1' THEN
        RAISE EXCEPTION 'Create maintenance_window FAILED, current database is not tempalte1';
    END IF;
    IF V_MAINTENANCE_WINDOW_EXIST = 0 AND CURRENT_DATABASE() = 'template1' THEN
        SELECT
            CASE
                WHEN NOW() < CURRENT_DATE + INTERVAL '22 HOUR' THEN CURRENT_DATE + INTERVAL '22 HOUR'
                ELSE CURRENT_DATE + INTERVAL '1 DAY 22 HOUR'
            END INTO V_MAINTENCE_WINDOW_START;
        --1. prepare for maintence window schedule
        SELECT 'freq=daily;interval=1;byhour='||V_HOUR||';byminute='||V_MINUTE||';bysecond='||V_SECOND INTO V_MAINTENCE_WINDOW_REPEAT;
        BEGIN
            SELECT
                CASE
                    WHEN VALUE = 1 THEN TRUE -- DBE_ILM_ADMIN.ILM_ENABLED
                    ELSE FALSE
                END INTO V_BE_SCHEDULE_ENABLE
                FROM PG_CATALOG.GS_ILM_PARAM WHERE IDX = 7; -- DBE_ILM_ADMIN.ENABLED
        EXCEPTION
            WHEN OTHERS THEN
                V_BE_SCHEDULE_ENABLE := FALSE;
        END;
        --2. Create ado window schedule
        DBE_SCHEDULER.CREATE_SCHEDULE(
            SCHEDULE_NAME => C_ADO_WINDOW_SCHEDULE_NAME,
            START_DATE => '9999-01-01 00:00:01',
            REPEAT_INTERVAL => NULL,
            END_DATE => NULL,
            COMMENTS => 'ado window schedule');
        --3. Create ado window program
        DBE_SCHEDULER.CREATE_PROGRAM(
            PROGRAM_NAME => C_ADO_WINDOW_PROGRAM_NAME,
            PROGRAM_TYPE => 'plsql_block',
            PROGRAM_ACTION => 'call prvt_ilm.be_execute_ilm();',
            NUMBER_OF_ARGUMENTS => 0,
            ENABLED => TRUE,
            COMMENTS => NULL);
        --4. Create maintenance window master job
        DBE_SCHEDULER.CREATE_JOB(
            JOB_NAME => C_MAINTENANCE_WINDOW_JOB_NAME,
            START_DATE => V_MAINTENCE_WINDOW_START,
            REPEAT_INTERVAL => V_MAINTENCE_WINDOW_REPEAT,
            END_DATE => NULL,
            JOB_TYPE => 'STORED_PROCEDURE'::TEXT,
            JOB_ACTION => 'prvt_ilm.be_active_ado_window'::TEXT,
            NUMBER_OF_ARGUMENTS => 0,
            ENABLED => V_BE_SCHEDULE_ENABLE,
            AUTO_DROP => FALSE,
            COMMENTS => 'maintenance window job');
    END IF;
END;

Automatic scheduling provides the following parameters for adjustment:

gaussdb=# SELECT * FROM gs_adm_ilmparameters;
        name        | value 
--------------------+-------
 EXECUTION_INTERVAL |    15
 RETENTION_TIME     |    30
 ENABLED            |     1
 POLICY_TIME        |     0
 ABS_JOBLIMIT       |    10
 JOB_SIZELIMIT      |   1024
 WIND_DURATION      |   240
 BLOCK_LIMITS       |    40
(8 rows)

EXECUTION_INTERVAL: interval for executing the automatic scheduling task. By default, the task is executed every 15 minutes.
RETENTION_TIME: interval for deleting historical compression task records. By default, historical compression task records are deleted every 30 days.
ENABLED: specifies whether automatic scheduling is enabled. The default value is ENABLED.
POLICY_TIME: time unit for policy evaluation, which is used for tests. The default unit is day.
ABS_JOBLIMIT: indicates the maximum number of compression tasks generated in a single evaluation. The default value is 10.
JOB_SIZELIMIT: I/O upper limit of a single compression task. The default value is 1 GB.
WIND_DURATION: duration of a single maintenance window.
BLOCK_LIMITS: upper limit of the instance-level row-store compression rate. The value ranges from 0 to 10000 (0 indicates that the rate is not limited). The default value is 40. Its unit is block/ms, indicating the maximum number of blocks that can be compressed per millisecond. The maximum rate is calculated as follows: BLOCK_LIMITS x 1000 x BLOCKSIZE. For example, if the default value is 40, the maximum rate is 320,000 KB/s (40 x 1000 x 8 KB).

The preceding parameters can be adjusted through the DBE_ILM_ADMIN.CUSTOMIZE_ILM() API.

By default, the maintenance window is opened at 22:00 (Beijing time) every day. You can use the SET_ATTRIBUTE interface provided by the DBE_SCHEDULER to set the maintenance window.

\c template1
 CALL DBE_ILM_ADMIN.DISABLE_ILM();
 CALL DBE_ILM_ADMIN.ENABLE_ILM();
DECLARE
    newtime timestamptz := CLOCK_TIMESTAMP() + to_interval('2 seconds');
BEGIN
    DBE_SCHEDULER.set_attribute(
        name          =>          'maintenance_window_job',
        attribute     =>          'start_date',
        value         =>          TO_CHAR(newtime, 'YYYY-MM-DD HH24:MI:SS')
    );
END;
/

Parent topic: Data Lifecycle Management: OLTP Table Compression

Previous topic: Feature Specifications

Next topic: Setting the Maintenance Window Parameters

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