SERVER-40105 Improve diagnostic information in currentOp for writeConflicts and prepareConflicts

2 files changed, 85 insertions, 1 deletions

diff --git a/jstests/core/txns/currentop_blocked_operations.js b/jstests/core/txns/currentop_blocked_operations.js
new file mode 100644
index 00000000000..8e51334bdff
--- /dev/null
+++ b/jstests/core/txns/currentop_blocked_operations.js
@@ -0,0 +1,83 @@
+/**
+ * Tests that currentOp reports debug information for operations that are blocked on transactions.
+ *
+ * @tags: [uses_transactions, uses_prepare_transaction]
+ */
+(function() {
+    "use strict";
+    load("jstests/core/txns/libs/prepare_helpers.js");
+
+    const dbName = "test";
+    const collName = "currentop_blocked_operations";
+    const testDB = db.getSiblingDB(dbName);
+    const testColl = testDB.getCollection(collName);
+
+    testColl.drop({writeConcern: {w: "majority"}});
+    assert.commandWorked(testDB.runCommand({create: collName, writeConcern: {w: "majority"}}));
+
+    const session = db.getMongo().startSession();
+    const sessionDB = session.getDatabase(dbName);
+    const sessionColl = sessionDB.getCollection(collName);
+
+    // Returns when the operation matching the 'matchExpr' is blocked, as evaluated by the
+    // 'isBlockedFunc'.
+    let waitForBlockedOp = function(matchExpr, isBlockedFunc) {
+        assert.soon(function() {
+            let cursor =
+                db.getSiblingDB("admin").aggregate([{$currentOp: {}}, {$match: matchExpr}]);
+            if (cursor.hasNext()) {
+                let op = cursor.next();
+                printjson(op);
+                return isBlockedFunc(op);
+            }
+            return false;
+        });
+    };
+
+    // This transaction will block conflicting non-transactional operations.
+    session.startTransaction();
+    assert.commandWorked(sessionColl.insert({_id: 2222}));
+
+    // This insert operation will encounter a WriteConflictException due to the unique key
+    // violation. It will block in an infinite write conflict loop until the transaction completes.
+    TestData.dbName = dbName;
+    TestData.collName = collName;
+    let awaitInsert = startParallelShell(function() {
+        let coll = db.getSiblingDB(TestData.dbName).getCollection(TestData.collName);
+        assert.commandWorked(coll.insert({_id: 2222, x: 0}));
+    });
+
+    // Wait for the counter to reach a high enough number to confirm the operation is retrying
+    // constantly.
+    waitForBlockedOp({"command.insert": collName}, function(op) {
+        return op.writeConflicts > 20;
+    });
+
+    assert.commandWorked(session.abortTransaction_forTesting());
+    awaitInsert();
+    assert.eq(1, testColl.find({_id: 2222, x: 0}).itcount());
+
+    // This prepared transaction will block conflicting non-transactional operations.
+    session.startTransaction();
+    assert.commandWorked(sessionColl.update({_id: 2222}, {$set: {x: 1}}));
+    PrepareHelpers.prepareTransaction(session);
+
+    // This update operation will encounter a prepare conflict due to the prepared transaction's
+    // modification to the same document. It will block without retrying until the prepared
+    // transaction completes.
+    TestData.dbName = dbName;
+    TestData.collName = collName;
+    let awaitUpdate = startParallelShell(function() {
+        let coll = db.getSiblingDB(TestData.dbName).getCollection(TestData.collName);
+        assert.commandWorked(coll.update({_id: 2222}, {$set: {x: 999}}));
+    });
+
+    // Expect at least one prepare conflict.
+    waitForBlockedOp({ns: testColl.getFullName(), op: "update"}, function(op) {
+        return op.prepareReadConflicts > 0;
+    });
+
+    assert.commandWorked(session.abortTransaction_forTesting());
+    awaitUpdate();
+    assert.eq(1, testColl.find({_id: 2222, x: 999}).itcount());
+})();
diff --git a/jstests/core/txns/write_conflicts_with_non_txns.js b/jstests/core/txns/write_conflicts_with_non_txns.js
index 5d7c1cdd589..c198c85084c 100644
--- a/jstests/core/txns/write_conflicts_with_non_txns.js
+++ b/jstests/core/txns/write_conflicts_with_non_txns.js
@@ -52,7 +52,8 @@
     // Returns true if a single document insert has started running on the server.
     function writeStarted() {
         return testDB.currentOp().inprog.some(op => {
-            return op.active && (op.ns === testColl.getFullName()) && (op.op === "insert");
+            return op.active && (op.ns === testColl.getFullName()) && (op.op === "insert") &&
+                (op.writeConflicts > 0);
         });
     }