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RATIS-2340. Add ReadIndexAsync executor for readIndex stateMachine query #1295

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RATIS-2340. Add ReadIndexAsync executor for readIndex stateMachine query #1295

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6 changes: 5 additions & 1 deletion ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1054,6 +1054,9 @@ private CompletableFuture<Long> getReadIndex(RaftClientRequest request, LeaderSt
return writeIndexCache.getWriteIndexFuture(request).thenCompose(leader::getReadIndex);
}

private final ExecutorService readAsyncExecutor = ConcurrentUtils.newThreadPoolWithMax(false,
Math.max(2, Runtime.getRuntime().availableProcessors()), "ReadAsync");

private CompletableFuture<RaftClientReply> readAsync(RaftClientRequest request) {
if (request.getType().getRead().getPreferNonLinearizable()
|| readOption == RaftServerConfigKeys.Read.Option.DEFAULT) {
Expand Down Expand Up @@ -1087,7 +1090,8 @@ private CompletableFuture<RaftClientReply> readAsync(RaftClientRequest request)

return replyFuture
.thenCompose(readIndex -> getReadRequests().waitToAdvance(readIndex))
.thenCompose(readIndex -> queryStateMachine(request))
.thenComposeAsync(ignored -> stateMachine.query(request.getMessage()), readAsyncExecutor)
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@szetszwo szetszwo Oct 1, 2025

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@symious , Since it is calling stateMachine.query(..), the StateMachine implementation could choose to run it with its own executor. If we use an executor here, then the stateMachine has no choice and is forced to run it with Ratis executor. So I suggest not to make this change.

.thenCompose(reply -> processQueryFuture(CompletableFuture.completedFuture(reply), request))
.exceptionally(e -> readException2Reply(request, e));
} else {
throw new IllegalStateException("Unexpected read option: " + readOption);
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