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- Getting Started
- Preparations
- Business Evaluation
- Network Preparation
- DTS Service Permission Preparation
- Database and Permission Preparation
- Configuring Binlog in Self-Built MySQL
- Data Migration
- Databases Supported by Data Migration
- Cross-Account TencentDB Instance Migration
- Migration to MySQL Series
- Migrating to MySQL
- Migrating to MariaDB
- Migrating to TDSQL-C for MySQL
- Migrating to TDSQL MySQL
- Migrating to TDSQL TDStore
- Advanced Operations for MySQL Series Migration
- Processing for MySQL Series Pre-Check Failure
- Database Connection Check
- Peripheral Check
- Version Check
- Source Instance Permission Check
- Partial Database Parameter Check
- Target Instance Permission Check
- Target Database Content Conflict Check
- Target Database Space Check
- Binlog Parameter Check
- Foreign Key Dependency Check
- View Check
- Advanced Object Check
- Warning Item Check
- TDSQL Proxy Check
- TDSQL Kernel Check
- DDL Ring Linkage Synchronization Detection for Same Database and Table Objects
- DDL Synchronization Conflict Detection for the Same Target and Same Database and Table Object
- Offline Migration of MySQL Data
- Migrating to PostgreSQL
- Migration from PostgreSQL to TencentDB for PostgreSQL
- Migration from TDSQL-C PostgreSQL to TencentDB for PostgreSQL
- PostgreSQL Physical Migration
- Processing for PostgreSQL Series Pre-Check Failure
- Database Connection Check
- Object Dependency Check
- Version Check
- Source or Target Instance Permission Check
- Incremental Migration Pre Check
- Structural Compatibility Check
- Structural Conflict Check
- Account Conflict Check
- Parameter Configuration Conflict Check
- Plugin Compatibility Check
- Multi Task Conflict Detection
- Long Transaction Check
- Migrating to MongoDB
- Migration from MongoDB to MongoDB
- Fix for Verification Failure
- MongoDB Connection Check
- Database/Table Content Conflict Check
- Source Database Node Role Check
- Oplog Check
- Source/Target Database Account Permission Check
- Database Version Check
- Database Capacity Check
- Target Database Load Check
- ShardKey Check
- Source Database Balancer Check
- Time Series Collection Verification
- Compression Algorithm Verification
- MongoDB Data Consistency Verification
- Migrating to SQL Server
- Migrating to TencentDB for Redis
- Migrating to KeeWiDB
- Task Management
- Task Status Description
- Viewing Task
- Configuring Task
- Verifying Task
- Start Task
- Retrying Task (MySQL)
- Retrying Task (Redis)
- Speed Limit (MySQL)
- Speed Limit (Redis)
- Complete Task
- Terminating Task
- Deleting Task
- Pausing Task
- Resuming Task
- Changing Configuration
- Terminating Task
- Deisolating Task
- Deleting Task
- Managing Tag
- Creating a Similar Task
- Viewing Log
- Data Sync
- Databases Supported by Data Sync
- Cross-Account TencentDB Instance Sync
- Sync to MySQL series
- Sync to MySQL
- Sync to MariaDB
- Sync to TDSQL-C for MySQL
- Sync to TDSQL for MySQL
- Sync to TDSQL TDStore
- MySQL Series Advanced Sync Operations
- MySQL series Pre Validation Failed Processing
- Database Connection Check
- Peripheral Check
- Version Check
- Source Instance Permission Check
- Partial Database Parameter Check
- Target Database Content Conflict Check
- Target Database Space Check
- Binlog Parameter Check
- Foreign Key Dependency Check
- View Check
- Advanced Object Check
- Warning Item Check
- TDSQL Proxy Check
- TDSQL kernel check
- DLL Ring Sync Check for Single Database/Table Object
- DLL Sync Conflict Check for Single Database/Table Object in the Same Target
- Synchronize to PostgreSQL
- Synchronization from PostgreSQL to PostgreSQL
- PostgreSQL Pre Validation does not Pass Processing
- Database Connection Check
- Object Dependency Check
- Version Check
- Source or Target Instance Permission Check
- Incremental Migration Pre Check
- Structural Compatibility Check
- Structural Conflict Check
- Account Conflict Check
- Parameter Configuration Conflict Check
- Plugin Compatibility Check
- Primary Key Dependency Check
- Check the Key Parameters of the Instance
- Multi Task Conflict Detection
- Synchronize to Kafka
- Task Management
- Task Status Description
- Viewing Task
- Configuring Task
- Verifying Task
- Starting Task
- Retrying Task (MySQL)
- Speed Limit
- Stopping Task
- Modify Sync configuration
- Pausing Task
- Resuming Task
- Resetting Task
- Deleting Task
- Changing Configuration
- Pay-as-You-Go to Monthly Subscription
- Terminating/Returning Instance
- Renewing Task
- Deisolating Task
- Deleting Instance
- Creating a Similar Task
- Viewing Log
- Deleting Task
- Data Subscription (Kafka Edition)
- Databases Supported by Data Subscription
- MySQL series Data Subscription
- Creating MySQL or TDSQL for MySQL Data Subscription
- Creating TDSQL for MySQL Data Subscription
- Creating MariaDB/Percona Data Subscription
- Consuming MySQL Data
- Advanced Subscription Operations
- Fix for Verification Failure
- Data Subscription for TDSQL PostgreSQL
- MongoDB Data Subscription
- Task Management
- Consumption Management
- Fix for Verification Failure
- Cutover Description
- Monitoring and Alarms
- Ops Management
- Practical Tutorial
- Synchronizing Local Database to the Cloud
- Creating Two-Way Sync Data Structure
- Creating Many-to-One Sync Data Structure
- Creating Multi-Site Active-Active IDC Architecture
- Selecting Data Sync Conflict Resolution Policy
- Using CLB as Proxy for Cross-Account Database Migration
- Migrating Self-Built Databases to Tencent Cloud Databases via CCN
- Best Practices for DTS Performance Tuning
- FAQs
- Error Handling
- API Documentation
- History
- Introduction
- API Category
- Making API Requests
- (NewDTS) Data Migration APIs
- DescribeMigrationJobs
- ModifyMigrationJob
- CompleteMigrateJob
- DescribeMigrationDetail
- CreateMigrationService
- CreateMigrateCheckJob
- DescribeMigrationCheckJob
- SkipCheckItem
- StartMigrateJob
- StopMigrateJob
- ResumeMigrateJob
- RecoverMigrateJob
- ModifyMigrateName
- ModifyMigrateJobSpec
- IsolateMigrateJob
- DestroyMigrateJob
- DescribeMigrateDBInstances
- PauseMigrateJob
- ContinueMigrateJob
- Data Sync APIs
- DescribeSyncJobs
- ModifySyncJobConfig
- CreateModifyCheckSyncJob
- DescribeModifyCheckSyncJobResult
- StartModifySyncJob
- CreateSyncJob
- ConfigureSyncJob
- CreateCheckSyncJob
- SkipSyncCheckItem
- DescribeCheckSyncJobResult
- StartSyncJob
- StopSyncJob
- ResumeSyncJob
- ResizeSyncJob
- RecoverSyncJob
- IsolateSyncJob
- DestroySyncJob
- PauseSyncJob
- ContinueSyncJob
- Data Consistency Check APIs
- Data Types
- Error Codes
- DTS API 2018-03-30
- SDK Documentation
- Service Agreement
Selecting Data Sync Conflict Resolution Policy
Last updated: 2024-07-08 15:54:46
Overview
DTS supports complex topology structures, including many-to-one, one-to-many, cascading one-way, two-way, and cascading two-way sync. In such a structure, data is written to multiple nodes at the same time, so primary key conflicts may occur. To address this issue, DTS detects primary key conflicts and provides the following resolution policies:
Primary Key Conflict Resolution Policy | Description | SQL Statement Rewrite During Conflict Resolution |
Report | During a sync task, if an INSERT statement in the source database has a primary key conflict with the data in the target database, the task will report an error and pause. You need to handle the conflict manually first before proceeding. | The task reports an error, and the SQL statement isn't rewritten. |
Ignore | During a sync task, if an INSERT statement in the source database has a primary key conflict with the data in the target database, the data inserted into the source database will be ignored, and the data in the target database will prevail. | If an INSERT statement has a primary key conflict, INSERT will be rewritten to INSERT IGNORE. |
Overwrite | During a sync task, if an INSERT or UPDATE statement has a primary key conflict with the data in the target database, the data in the target database will be overwritten by the inserted or updated data in the source database. | If an INSERT or UPDATE statement has a primary key conflict, INSERT or UPDATE will be rewritten to REPLACE INTO or DELETE + REPLACE INTO respectively. |
Examples
Primary key conflict resolution policies take effect only for INSERT and UPDATE primary key conflicts but not in non-conflict scenarios. After a policy is applied, the task can report an error or proceed once a conflict occurs. Below are examples of two primary key conflict scenarios with results under different policies.
INSERT primary key conflict
An A > B one-way sync with
ID as the primary key is created. When an INSERT statement in A has a primary key conflict with the data in B during data sync, DTS will handle the conflict according to the configured conflict resolution policy.
The respective sync results in B under different policies are as detailed below:
Report: The task reports an error, and the data in B remains unchanged (ID=1, Price=10).
Ignore: The task ignores the data with the same primary key in A, and the data in B remains unchanged (ID=1, Price=10).
Overwrite: The task overwrites the data in B with the data with the same primary key in A, and the data in B becomes
ID=1, Price=20.UPDATE primary key conflict
In some scenarios, you may modify the primary key, leading to a primary key conflict. For example, the primary key in A is updated (ID=1 > ID=2), which will conflict with the data with primary key
ID being 2 in B.
The respective sync results in B under different policies are as detailed below:
Report: The task reports an error, and the data in B remains unchanged.
Ignore: The task reports an error, and the data in B remains unchanged. Note that DTS ignores the conflict in this case.
Overwrite: The task overwrites the data in B with the data with the same primary key in A, and only the data with primary key
2 exists in B (ID=2, Price=10).Conflict Resolution Policy and Data Consistency
In complex data architectures such as 2-region-3-DC and multi-site active-active architectures, data may need to be written to three or more nodes at the same time, and it is crucial to guarantee the data consistency across multiple nodes. Many users believe that they can use a primary key conflict resolution policy to sync the data on the specified node to other nodes, but this actually doesn't work.
In the following two-way sync scenario, the Overwrite policy is set for both A > B and B > A sync. If different data records with the primary key
1 are inserted into nodes A and B at the same time, they will be swapped with each other between A and B eventually.
In real-world scenarios, to implement data consistency across nodes, you generally need to partition the database by primary key, introduce additional coordination mechanisms such as data overwriting by version number, and use other methods in addition to a conflict resolution policy.
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