SERVER-39719 Ensure that a node performing an initial sync from a secondary with a in-progress index build creates the index before initial sync is done

(cherry picked from commit efefc4f94203c3e6119916b89255017d117e982f)

2 files changed, 97 insertions, 0 deletions

diff --git a/jstests/replsets/secondary_as_sync_source.js b/jstests/replsets/secondary_as_sync_source.js
new file mode 100644
index 00000000000..6f446842daa
--- /dev/null
+++ b/jstests/replsets/secondary_as_sync_source.js
@@ -0,0 +1,88 @@
+/**
+ * Tests that a new replica set member performing an initial sync from a secondary node as the sync
+ * source, which has an in-progress index build will also build the index as part of the initial
+ * sync operation.
+ * @tags: [requires_replication]
+ */
+(function() {
+    'use strict';
+
+    load("jstests/replsets/rslib.js");
+
+    const dbName = "test";
+    const collName = "coll";
+
+    const firstIndexName = "_first";
+
+    function addTestDocuments(db) {
+        let size = 100;
+        jsTest.log("Creating " + size + " test documents.");
+        var bulk = db.getCollection(collName).initializeUnorderedBulkOp();
+        for (var i = 0; i < size; ++i) {
+            bulk.insert({i: i});
+        }
+        assert.writeOK(bulk.execute());
+    }
+
+    let replSet = new ReplSetTest({name: "indexBuilds", nodes: 2, useBridge: true});
+    let nodes = replSet.nodeList();
+
+    replSet.startSet({startClean: true});
+    replSet.initiate({
+        _id: "indexBuilds",
+        members: [
+            {_id: 0, host: nodes[0]},
+            {_id: 1, host: nodes[1], votes: 0, priority: 0},
+        ]
+    });
+
+    let primary = replSet.getPrimary();
+    let primaryDB = primary.getDB(dbName);
+
+    let secondary = replSet.getSecondary();
+    let secondaryDB = secondary.getDB(dbName);
+
+    addTestDocuments(primaryDB);
+
+    jsTest.log("Hanging index builds on the secondary node");
+    assert.commandWorked(secondaryDB.adminCommand(
+        {configureFailPoint: "hangAfterStartingIndexBuild", mode: "alwaysOn"}));
+
+    jsTest.log("Beginning index build: " + firstIndexName);
+    assert.commandWorked(primaryDB.runCommand({
+        createIndexes: collName,
+        indexes: [{key: {i: 1}, name: firstIndexName, background: true}],
+        writeConcern: {w: 2}
+    }));
+
+    jsTest.log("Adding a new node to the replica set");
+    let newNode = replSet.add({rsConfig: {votes: 0, priority: 0}});
+
+    // Ensure that the new node and primary cannot communicate to each other.
+    newNode.disconnect(primary);
+
+    replSet.reInitiate();
+
+    // Wait for the new node to finish initial sync.
+    waitForState(newNode, ReplSetTest.State.SECONDARY);
+
+    // Let the 'secondary' finish its index build.
+    jsTest.log("Removing index build hang on the secondary node to allow it to finish");
+    assert.commandWorked(
+        secondaryDB.adminCommand({configureFailPoint: "hangAfterStartingIndexBuild", mode: "off"}));
+
+    // Wait for the index builds to finish.
+    replSet.waitForAllIndexBuildsToFinish(dbName, collName);
+    jsTest.log("Checking if the indexes match between the new node and the secondary node");
+
+    let newNodeDB = newNode.getDB(dbName);
+    jsTest.log("New nodes indexes:");
+    printjson(newNodeDB.getCollection(collName).getIndexes());
+    jsTest.log("Secondary nodes indexes:");
+    printjson(secondaryDB.getCollection(collName).getIndexes());
+
+    assert.eq(newNodeDB.getCollection(collName).getIndexes().length,
+              secondaryDB.getCollection(collName).getIndexes().length);
+
+    replSet.stopSet();
+})();
diff --git a/src/mongo/shell/replsettest.js b/src/mongo/shell/replsettest.js
index aeae8d76eec..5848b2f288e 100644
--- a/src/mongo/shell/replsettest.js
+++ b/src/mongo/shell/replsettest.js
@@ -1475,6 +1475,15 @@ var ReplSetTest = function(opts) {
         }, "awaiting replication", timeout);
     };
 
+    this.waitForAllIndexBuildsToFinish = function(dbName, collName) {
+        // Run a no-op command and wait for it to be applied on secondaries. Due to the asynchronous
+        // completion nature of indexes on secondaries, we can guarantee an index build is complete
+        // on all secondaries once all secondaries have applied this collMod command.
+        assert.commandWorked(this.getPrimary().getDB(dbName).runCommand(
+            {collMod: collName, usePowerOf2Sizes: true}));
+        this.awaitReplication();
+    };
+
     this.getHashesUsingSessions = function(sessions, dbName, {
         filterCapped: filterCapped = true,
         filterMapReduce: filterMapReduce = true,