Compute
Elastic Cloud Server
Huawei Cloud Flexus
Bare Metal Server
Auto Scaling
Image Management Service
Dedicated Host
FunctionGraph
Cloud Phone Host
Huawei Cloud EulerOS
Networking
Virtual Private Cloud
Elastic IP
Elastic Load Balance
NAT Gateway
Direct Connect
Virtual Private Network
VPC Endpoint
Cloud Connect
Enterprise Router
Enterprise Switch
Global Accelerator
Management & Governance
Cloud Eye
Identity and Access Management
Cloud Trace Service
Resource Formation Service
Tag Management Service
Log Tank Service
Config
OneAccess
Resource Access Manager
Simple Message Notification
Application Performance Management
Application Operations Management
Organizations
Optimization Advisor
IAM Identity Center
Cloud Operations Center
Resource Governance Center
Migration
Server Migration Service
Object Storage Migration Service
Cloud Data Migration
Migration Center
Cloud Ecosystem
KooGallery
Partner Center
User Support
My Account
Billing Center
Cost Center
Resource Center
Enterprise Management
Service Tickets
HUAWEI CLOUD (International) FAQs
ICP Filing
Support Plans
My Credentials
Customer Operation Capabilities
Partner Support Plans
Professional Services
Analytics
MapReduce Service
Data Lake Insight
CloudTable Service
Cloud Search Service
Data Lake Visualization
Data Ingestion Service
GaussDB(DWS)
DataArts Studio
Data Lake Factory
DataArts Lake Formation
IoT
IoT Device Access
Others
Product Pricing Details
System Permissions
Console Quick Start
Common FAQs
Instructions for Associating with a HUAWEI CLOUD Partner
Message Center
Security & Compliance
Security Technologies and Applications
Web Application Firewall
Host Security Service
Cloud Firewall
SecMaster
Anti-DDoS Service
Data Encryption Workshop
Database Security Service
Cloud Bastion Host
Data Security Center
Cloud Certificate Manager
Edge Security
Managed Threat Detection
Blockchain
Blockchain Service
Web3 Node Engine Service
Media Services
Media Processing Center
Video On Demand
Live
SparkRTC
MetaStudio
Storage
Object Storage Service
Elastic Volume Service
Cloud Backup and Recovery
Storage Disaster Recovery Service
Scalable File Service Turbo
Scalable File Service
Volume Backup Service
Cloud Server Backup Service
Data Express Service
Dedicated Distributed Storage Service
Containers
Cloud Container Engine
SoftWare Repository for Container
Application Service Mesh
Ubiquitous Cloud Native Service
Cloud Container Instance
Databases
Relational Database Service
Document Database Service
Data Admin Service
Data Replication Service
GeminiDB
GaussDB
Distributed Database Middleware
Database and Application Migration UGO
TaurusDB
Middleware
Distributed Cache Service
API Gateway
Distributed Message Service for Kafka
Distributed Message Service for RabbitMQ
Distributed Message Service for RocketMQ
Cloud Service Engine
Multi-Site High Availability Service
EventGrid
Dedicated Cloud
Dedicated Computing Cluster
Business Applications
Workspace
ROMA Connect
Message & SMS
Domain Name Service
Edge Data Center Management
Meeting
AI
Face Recognition Service
Graph Engine Service
Content Moderation
Image Recognition
Optical Character Recognition
ModelArts
ImageSearch
Conversational Bot Service
Speech Interaction Service
Huawei HiLens
Video Intelligent Analysis Service
Developer Tools
SDK Developer Guide
API Request Signing Guide
Terraform
Koo Command Line Interface
Content Delivery & Edge Computing
Content Delivery Network
Intelligent EdgeFabric
CloudPond
Intelligent EdgeCloud
Solutions
SAP Cloud
High Performance Computing
Developer Services
ServiceStage
CodeArts
CodeArts PerfTest
CodeArts Req
CodeArts Pipeline
CodeArts Build
CodeArts Deploy
CodeArts Artifact
CodeArts TestPlan
CodeArts Check
CodeArts Repo
Cloud Application Engine
MacroVerse aPaaS
KooMessage
KooPhone
KooDrive

CLUSTER

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

Description

  • Clusters a table based on an index.
  • CLUSTER instructs GaussDB to cluster the table specified by table_name based on the index specified by index_name. The index must have been defined by table_name.
  • When a table is clustered, it is physically reordered based on the index information. Clustering is a one-time operation. When the table is subsequently updated, the changes are not clustered. That is, no attempt is made to store new or updated rows according to their index order.
  • When a table is clustered, GaussDB records which index the table was clustered by. CLUSTER table_name reclusters the clustered index that was previously recorded in the table. You can also use ALTER TABLE table_name CLUSTER on index_name to set the index of a specified table for subsequent cluster operations, or use ALTER TABLE table_name SET WITHOUT CLUSTER to clear the previously clustered index of a specified table.
  • If CLUSTER does not contain parameters, all tables that have been clustered in the database owned by the current user will be reprocessed. If a system administrator uses this command, all clustered tables are reclustered.
  • When a table is being clustered, an ACCESS EXCLUSIVE lock is acquired on it. This prevents any other database operations (both read and write) from being performed on the table until the CLUSTER operation is finished.

Precautions

  • Only row-store B-tree indexes support CLUSTER.
  • In the case where you are accessing single rows randomly within a table, the actual order of the data in the table is unimportant. However, if there are many accesses to some data and an index groups the data, using the CLUSTER index improves performance.
  • If an index you request from a table is a range, or a single indexed value that has multiple rows that match, CLUSTER will help because once the index identifies the table page for the first row that matches, all other rows that match are probably already on the same table page, and so you save disk accesses and speed up the query.
  • During clustering, the system creates a temporary backup of the table created in the index sequence and a temporary backup of each index in the table. Therefore, ensure that the disk has sufficient free space during clustering, which is at least the sum of the table size and all index sizes.
  • CLUSTER records which indexes have been used for clustering. Therefore, you can manually specify indexes for the first time, cluster specified tables, and set a maintenance script that will be executed periodically. You only need to run the CLUSTER command without parameters. In this way, tables that you want to periodically cluster can be automatically updated.
  • The optimizer records table clustering statistics. After clustering a table, you need to execute the ANALYZE operation to ensure that the optimizer has the latest clustering information. Otherwise, the optimizer may select a non-optimal query plan.
  • CLUSTER cannot be executed in transactions.
  • If the xc_maintenance_mode parameter is not enabled, CLUSTER skips all system catalogs.

Syntax

  • Cluster a table.
    1
    CLUSTER [ VERBOSE ] table_name [ USING index_name ];
    
  • Cluster a partition.
    1
    CLUSTER [ VERBOSE ] table_name PARTITION ( partition_name ) [ USING index_name ];
    
  • Recluster a table.
    1
    CLUSTER [ VERBOSE ];
    

Parameters

  • VERBOSE

    Enables the display of progress messages.

  • table_name

    Specifies the table name.

    Value range: an existing table name

  • index_name

    Specifies the index name.

    Value range: an existing index name

  • partition_name

    Specifies the partition name.

    Value range: an existing partition name

Examples

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
-- Create a partitioned table.
gaussdb=# CREATE TABLE tpcds.inventory_p1
(
    INV_DATE_SK               INTEGER               NOT NULL,
    INV_ITEM_SK               INTEGER               NOT NULL,
    INV_WAREHOUSE_SK          INTEGER               NOT NULL,
    INV_QUANTITY_ON_HAND      INTEGER
)
DISTRIBUTE BY HASH(INV_ITEM_SK)
PARTITION BY RANGE(INV_DATE_SK)
(
        PARTITION P1 VALUES LESS THAN(2451179),
        PARTITION P2 VALUES LESS THAN(2451544),
        PARTITION P3 VALUES LESS THAN(2451910),
        PARTITION P4 VALUES LESS THAN(2452275),
        PARTITION P5 VALUES LESS THAN(2452640),
        PARTITION P6 VALUES LESS THAN(2453005),
        PARTITION P7 VALUES LESS THAN(MAXVALUE)
);

-- Create an index named ds_inventory_p1_index1.
gaussdb=# CREATE INDEX ds_inventory_p1_index1 ON tpcds.inventory_p1 (INV_ITEM_SK) LOCAL;

-- Cluster the tpcds.inventory_p1 table.
gaussdb=# CLUSTER tpcds.inventory_p1 USING ds_inventory_p1_index1;

-- Cluster the p3 partition.
gaussdb=# CLUSTER tpcds.inventory_p1 PARTITION (p3) USING ds_inventory_p1_index1;

-- Cluster the tables that can be clustered in the database.
gaussdb=# CLUSTER;

-- Delete the index.
gaussdb=# DROP INDEX tpcds.ds_inventory_p1_index1;

-- Drop the partitioned table.
gaussdb=# DROP TABLE tpcds.inventory_p1;

We use cookies to improve our site and your experience. By continuing to browse our site you accept our cookie policy. Find out more

Feedback

Feedback

Feedback

0/500

Selected Content

Submit selected content with the feedback