SERVER-40366: Log when the flow control sustainer point is not moving.

1 files changed, 57 insertions, 0 deletions

diff --git a/jstests/noPassthrough/flow_control_logging.js b/jstests/noPassthrough/flow_control_logging.js
new file mode 100644
index 00000000000..b22758d5a89
--- /dev/null
+++ b/jstests/noPassthrough/flow_control_logging.js
@@ -0,0 +1,57 @@
+/**
+ * Tests that flow control outputs a log when it is maximally engaged on some cadence.
+ *
+ * @tags: [
+ *   requires_replication,
+ *   requires_majority_read_concern,
+ * ]
+ */
+(function() {
+    "use strict";
+
+    load("jstests/libs/check_log.js");
+
+    const replSet = new ReplSetTest({name: "flow_control_logging", nodes: 3});
+    replSet.startSet({
+        setParameter: {
+            enableFlowControl: true,
+            flowControlSamplePeriod:
+                1,  // Increase resolution to detect lag in a light write workload.
+            flowControlWarnThresholdSeconds: 1,
+            // Configure flow control to engage after one second of lag.
+            flowControlTargetLagSeconds: 1,
+            flowControlThresholdLagPercentage: 1,
+            // Use a speedy no-op writer to avoid needing a robust background writer.
+            writePeriodicNoops: true,
+            periodicNoopIntervalSecs:
+                2  // replSet.initiate() can hang with a one second interval for reasons.
+        }
+    });
+    replSet.initiate();
+
+    // Stop replication which will pin the commit point.
+    for (let sec of replSet.getSecondaries()) {
+        assert.commandWorked(sec.adminCommand({
+            configureFailPoint: "pauseBatchApplicationAfterWritingOplogEntries",
+            mode: "alwaysOn"
+        }));
+    }
+
+    const timeoutMilliseconds = 30 * 1000;
+    // The test has stopped replication and the primary's no-op writer is configured to create an
+    // oplog entry every other second. Once the primary notices the sustainer rate is not moving, it
+    // should start logging a warning once per second. This check waits for two log messages to make
+    // sure the appropriate state variables are being reset.
+    checkLog.containsWithCount(replSet.getPrimary(),
+                               "Flow control is engaged and the sustainer point is not moving.",
+                               2,
+                               timeoutMilliseconds);
+
+    // Restart replication so the replica set will shut down.
+    for (let sec of replSet.getSecondaries()) {
+        assert.commandWorked(sec.adminCommand(
+            {configureFailPoint: "pauseBatchApplicationAfterWritingOplogEntries", mode: "off"}));
+    }
+
+    replSet.stopSet();
+})();