Several methods to achieve capacity expansion without shutdown in SQL

Unstopped capacity expansion is a method of dynamically increasing resources to improve system performance and capacity without affecting the normal operation of the system. In database systems, non-stop expansion usually involves the expansion of sharding. The following are some common implementation methods and steps.

1. Add new nodes and reshape

When the system needs to expand capacity, new database nodes can be added and resharded data.

step:

• Add a new node：

  • Add a new DB instance to the cluster.
  • Configure a new instance to communicate with an existing instance.

• Data replication：

  • Copy existing data to a new node. This usually uses an asynchronous replication method to avoid excessive load on existing systems.
  • You can use tools (such as MySQL'smysqldumporxtrabackup) to backup and restore data.

• Reslicing：

  • Recalculate the sharding rules for data and reassign part of the existing data to the new node.
  • Migrate data from old shards to new shards through the data migration tool.
  • Use the "dual-write" strategy during the migration process, that is, all write operations write to both the old and new shards to ensure data consistency.

• Update routing rules：

  • Updates the application's routing rules so that it can recognize and access new shards.
  • You can use sharding middleware (such as ShardingSphere, Vitess) to manage routing rules.

• Monitoring and verification：

  • Monitor the data migration process to ensure data integrity and consistency.
  • Verify the migrated data to ensure the correctness and performance of new shards.

Sample code (Java):

Here is a simple example that demonstrates how to dynamically update routing rules to support new shards.

import ;
import ;

public class ShardingRouter {

    private Map<Integer, String> shardMap;

    public ShardingRouter() {
        shardMap = new HashMap<>();
        // Initialize sharding rules, for example:        (0, "db0");
        (1, "db1");
    }

    public String getShard(int userId) {
        int shardId = userId % ();
        return (shardId);
    }

    public void addShard(String dbName) {
        int newShardId = ();
        (newShardId, dbName);
    }

    public static void main(String[] args) {
        ShardingRouter router = new ShardingRouter();
        ("db2"); // Add new shards
        int userId = 12345;
        String shard = (userId);
        ("User " + userId + " is assigned to shard: " + shard);
    }
}

2. Use shard middleware

Using sharding middleware can simplify the process of sharding and scaling. These middleware usually provide automatic capacity expansion and load balancing.

Common sharding middleware:

• ShardingSphere: Apache ShardingSphere provides data sharding, read and write separation, data encryption and other functions, and supports unstoppable capacity expansion.
• Vitess:Vitess is an open source distributed database solution that is widely used in MySQL and supports horizontal scaling and high availability.
• Citus:Citus is a PostgreSQL extension plug-in that supports large-scale data sharding and distributed queries.

Example: Using ShardingSphere

Here are the basic steps for sharding and scaling using ShardingSphere.

• Configure sharding rules：
  • Define sharding policies and routing rules.
  • Configure ShardingSphere's sharding rules YAML file.

rules:
  sharding:
    tables:
      user:
        actualDataNodes: ds${0..2}.user${0..2}
        tableStrategy:
          standard:
            shardingColumn: user_id
            shardingAlgorithmName: user-id-hash
        keyGenerateStrategy:
          column: user_id
          keyGeneratorName: snowflake
    shardingAlgorithms:
      user-id-hash:
        type: HASH_MOD
        props:
          sharding-count: 3
    keyGenerators:
      snowflake:
        type: SNOWFLAKE

• Start ShardingSphere：

  • Start the ShardingSphere cluster and load sharding rules.

• Add new shard node：

  • Dynamically add new database nodes to the ShardingSphere cluster.
  • renewactualDataNodesConfiguration, including new shards.

• Data migration：

  • Use the data migration tool provided by ShardingSphere to migrate data to a new shard.

3. Online migration and double write strategies

During the expansion process, online migration and double write strategies can be used to ensure data consistency and integrity.

Online migration steps:

• Start writing double：

  • Before the data migration begins, the configuration application writes both the old shard and the new shard.

• Data migration：

  • Use data migration tools (e.g.gh-ost、pt-online-schema-change) Migrate data from the old shard to the new shard.

• Verify data：

  • Verify the data integrity and consistency of new shards through verification tools.

• Switch routes：

  • After the data migration is completed, the routing rules are updated so that all read and write operations are pointed to the new shard.

• Stop double writing：

  • After verification is correct, stop writing operations of the old shard and complete the migration.

Summarize

Unstoppable capacity expansion involves multiple steps such as adding new nodes, reslicing, updating routing rules, and data migration. Through reasonable sharding strategies and the use of shard middleware, efficient capacity expansion can be achieved without shutdown. At the same time, online migration and double-write strategies are key to ensuring data consistency and integrity.

This is the end of this article about several methods of implementing capacity expansion without stopping in SQL. For more related content on SQL, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!