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Version: Nightly

Noop WAL

Noop WAL is a special WAL provider for emergency situations when the configured WAL provider becomes temporarily unavailable. It does not store any WAL data.

Availability​

Noop WAL is only available in cluster mode, not in standalone mode.

Use Cases​

  • Temporary WAL Unavailability: When the WAL provider (e.g., Kafka) is temporarily unavailable, switch the Datanode to Noop WAL to keep the cluster running.
  • Testing and Development: Useful for testing scenarios where WAL persistence is not required.

Data Loss Warning​

When using Noop WAL, all unflushed data will be lost when the Datanode is shutdown or restarted. Only use this provider temporarily when the normal WAL provider is unavailable. Not recommended for production use except in emergency situations.

Configuration​

To configure Noop WAL for a Datanode:

[wal]
provider = "noop"

In a GreptimeDB cluster, WAL configuration has two parts:

  • Metasrv - Generates WAL metadata for new regions. Should be set to raft_engine or kafka.
  • Datanode - Reads and writes WAL data. Configure as noop when the WAL provider is unavailable.

Note: Noop WAL can only be configured on Datanode, not on Metasrv. When using Noop WAL on Datanode, Metasrv continues using its configured WAL provider.

Best Practices​

  • Flush regions regularly using admin flush_table() or admin flush_region() to minimize data loss.
  • Switch back to the normal WAL provider as soon as it becomes available.