RATIS-2176. Update doc for raft.server.log.appender.wait-time.min. by jojochuang · Pull Request #1181

RATIS-2176. Update doc for raft.server.log.appender.wait-time.min. by jojochuang · Pull Request #1181 · apache/ratis

What changes were proposed in this pull request?

RATIS-1886 updated the default value of raft.server.log.appender.wait-time.min but didn't update the doc.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/RATIS-2176

How was this patch tested?

User doc change. No production code change.

…he same peer as the current valid leader (apache#1024)

		\| Default \| 10ms \|
		\| Property \| `raft.server.log.appender.wait-time.min` \|
		\|:----------------\|:---------------------------------------------------------------------------\|
		\| Description \| wait time between two subsequent AppendEntries. Must be a positive number. \|

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@jojochuang , thanks a lot for working on this!

This conf has two purposes:

wait time between two subsequent AppendEntries, and
set to waitForReady in GrpcLogAppender (for the sleep waiting a gRPC stream to ready).

For (1), zero is allowed. For (2), zero becomes 1ms.

Do you think that the usage in (2) is problematic? If yes, we may use a different conf.

Actually, just updating the doc is not sufficient.

GrpcLogAppender.StreamObservers.onNext() calls sleep for waitForReady, but internally it uses Thread.sleep() so it is never going to be less than one millisecond.

I'm looking at an Ozone cluster where follower DataNode completes the append follower_append_entry_latency just 0.66ms, but the leader's log_appender_latency is 1.36ms. Clearly, the one millisecond sleep granulaity is the problem for the append latency.

Comment on lines -356 to +358

		sleep(waitForReady, isHeartBeat);
		//sleep(waitForReady, isHeartBeat);
		LockSupport.parkNanos(waitForReady.toLong(TimeUnit.NANOSECONDS));

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@jojochuang , thanks for the update! Sorry that I missed the new change earlier.

How about changing it in the sleep(..) method?

@@ -408,12 +409,9 @@ public class GrpcLogAppender extends LogAppenderBase {
 
   private static void sleep(TimeDuration waitTime, boolean heartbeat)
       throws InterruptedIOException {
-    try {
-      waitTime.sleep();
-    } catch (InterruptedException e) {
-      Thread.currentThread().interrupt();
-      throw IOUtils.toInterruptedIOException(
-          "Interrupted appendLog, heartbeat? " + heartbeat, e);
+    LockSupport.parkNanos(waitTime.toLong(TimeUnit.NANOSECONDS));
+    if (Thread.currentThread().isInterrupted()) {
+      throw new InterruptedIOException("Interrupted appendLog, heartbeat? " + heartbeat);
     }
   }

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		\| Default \| 10ms \|
		\| Property \| `raft.server.log.appender.wait-time.min` \|
		\|:----------------\|:---------------------------------------------------------------------------\|
		\| Description \| wait time between two subsequent AppendEntries. Must be a positive number. \|