Read-After-Write Consistency Support
This feature ensures that a read operation by a client reflects the latest successful write by the same client, even if that write has not yet been fully committed across the entire Raft group. This provides a stronger consistency guarantee for individual client sessions.
Interface Methods
To utilize read-after-write consistency, the following methods are available in the client APIs:
Asynchronous API (org.apache.ratis.client.api.AsyncApi)
CompletableFuture sendReadAfterWrite(Message message);
Sends the given readonly message asynchronously to the Raft service. The result will be read-after-write consistent, i.e., reflecting the latest successful write by the same client.
Blocking API (org.apache.ratis.client.api.BlockingApi)
RaftClientReply sendReadAfterWrite(Message message) throws IOException;
Sends the given readonly message to the Raft service. The result will be read-after-write consistent, i.e., reflecting the latest successful write by the same client.
Configuration
To configure the read-after-write consistency feature, the following property can be set in RaftServerConfigKeys:
RaftServerConfigKeys.ReadAfterWriteConsistent
| Property | Description | Type | Default |
|---|---|---|---|
raft.server.read.read-after-write-consistent.write-index-cache.expiry-time | Expiration time for the server's memorized last written index of a specific client. Must be larger than Read.TIMEOUT_DEFAULT. | TimeDuration | 60s |
Methods to set/get this property:
static TimeDuration writeIndexCacheExpiryTime(RaftProperties properties);
static void setWriteIndexCacheExpiryTime(RaftProperties properties, TimeDuration expiryTime);