如何在Ignite集群中修改Sample表备份数从1改为0（避免删表）

Great question! Since Ignite's ALTER TABLE doesn't support modifying backup counts directly (as backups are a cache-level configuration, not a table schema property), we can adjust the underlying cache tied to your Sample table. Here's a safe, step-by-step approach to do this without dropping the table or losing data:

Prerequisites #

• Ensure your 8-node Ignite cluster is in ACTIVE state.
• Schedule this operation during low-traffic hours—rebalancing 300 million records will consume significant cluster resources.
• (Optional but highly recommended) Take a snapshot of the cache first to safeguard your data:

  // Using Java API
  ignite.snapshot().createSnapshot("sample_backup_snapshot");
  

  Or via the Visor command line tool:

  visor> snapshot -create sample_backup_snapshot -c SampleCache
  

Step 1: Verify Current Cache Configuration #

First, confirm the current backup count for your SampleCache using Visor:

visor> cache -c SampleCache

Look for the backups field in the output—it should show 1.

Step 2: Update Cache Configuration to Set Backups=0 #

You can do this either via the Java API or Visor CLI:

Option 1: Java API #

Ignite ignite = Ignition.ignite();

// Fetch the existing cache configuration
CacheConfiguration<?, ?> cacheCfg = ignite.cache("SampleCache").getConfiguration(CacheConfiguration.class);

// Update backup count to 0 (keep all other configuration settings unchanged)
cacheCfg.setBackups(0);

// Apply the updated configuration to the cache
ignite.reconfigureCache("SampleCache", cacheCfg);

Option 2: Visor CLI #

1. Export the current cache configuration to an XML file:

   visor> cache -export SampleCache -file sample_cache_config.xml
   

2. Open sample_cache_config.xml in a text editor, find the <backups>1</backups> line, and change it to <backups>0</backups>.
3. Reconfigure the cache with the modified file:

   visor> cache -reconfigure SampleCache -file sample_cache_config.xml
   

Step 3: Trigger Cache Rebalancing #

After updating the configuration, trigger rebalancing so the cluster can clean up the now-unneeded backup partitions:

# Via Visor
visor> cache -rebalance SampleCache

Or via Java API:

ignite.cache("SampleCache").rebalance();

Step 4: Verify the Change #

Once rebalancing completes, check the cache configuration again to confirm backups are set to 0:

visor> cache -c SampleCache

Also, validate data integrity by running a count query on your Sample table to ensure all 300 million records are still present:

SELECT COUNT(*) FROM Sample;

Key Notes #

• Backups are a cache-level setting: The Sample table relies on SampleCache for storage, so modifying the cache's backup count directly affects the table's redundancy.
• No data loss: We're only removing redundant backup partitions (primary partitions remain intact), so your data will stay safe as long as all primary nodes are available during the process.
• Performance impact: Rebalancing large datasets will increase network and disk I/O—plan accordingly to minimize disruption.

内容的提问来源于stack exchange，提问作者rai2048