SERVER-31836 Always dispatch sorted tailable awaitdata getMores to the shards with timeouts of at most 1 second

1 files changed, 9 insertions, 1 deletions

diff --git a/src/mongo/s/query/async_results_merger.cpp b/src/mongo/s/query/async_results_merger.cpp
index 8bdc8e69353..241f09f209b 100644
--- a/src/mongo/s/query/async_results_merger.cpp
+++ b/src/mongo/s/query/async_results_merger.cpp
@@ -129,7 +129,15 @@ Status AsyncResultsMerger::setAwaitDataTimeout(Milliseconds awaitDataTimeout) {
                       "maxTimeMS can only be used with getMore for tailable, awaitData cursors");
     }
 
-    _awaitDataTimeout = awaitDataTimeout;
+    // For sorted tailable awaitData cursors on multiple shards, cap the getMore timeout at 1000ms.
+    // This is to ensure that we get a continuous stream of updates from each shard with their most
+    // recent optimes, which allows us to return sorted $changeStream results even if some shards
+    // are yet to provide a batch of data. If the timeout specified by the client is greater than
+    // 1000ms, then it will be enforced elsewhere.
+    _awaitDataTimeout = (!_params->sort.isEmpty() && _remotes.size() > 1u
+                             ? std::min(awaitDataTimeout, Milliseconds{1000})
+                             : awaitDataTimeout);
+
     return Status::OK();
 }