2 files changed, 154 insertions, 0 deletions
diff --git a/jstests/sharding/reshard_collection_joins_existing_operation.js b/jstests/sharding/reshard_collection_joins_existing_operation.js
new file mode 100644
index 00000000000..0ee7dce2b64
--- /dev/null
+++ b/jstests/sharding/reshard_collection_joins_existing_operation.js
@@ -0,0 +1,115 @@
+/**
+ * Tests that if a _configsvrReshardCollection command is issued and then the same command gets
+ * issued again, the second command issued joins with the instance of resharding already in
+ * progress.
+ *
+ * Use _configsvrReshardCollection instead of reshardCollection to exercise the behavior of the
+ * config server in the absence of the distributed lock taken by _shardsvrReshardCollection on the
+ * primary shard for the database.
+ *
+ * @tags: [
+ *   requires_fcv_49,
+ *   uses_atclustertime,
+ * ]
+ */
+(function() {
+"use strict";
+
+load("jstests/libs/discover_topology.js");
+load("jstests/libs/parallelTester.js");
+load("jstests/sharding/libs/resharding_test_fixture.js");
+
+// Generates a new thread to run _configsvrReshardCollection.
+const makeConfigsvrReshardCollectionThread = (mongosConnString, configsvrReshardCollectionCmd) => {
+    return new Thread((mongosConnString, configsvrReshardCollectionCmd) => {
+        load("jstests/libs/discover_topology.js");
+        const mongos = new Mongo(mongosConnString);
+        const topology = DiscoverTopology.findConnectedNodes(mongos);
+        const configsvr = new Mongo(topology.configsvr.nodes[0]);
+        assert.commandWorked(configsvr.adminCommand(configsvrReshardCollectionCmd));
+    }, mongosConnString, configsvrReshardCollectionCmd);
+};
+
+const constructTempReshardingNs = (dbName, collName) => {
+    const sourceCollectionUUID = getUUIDFromListCollections(dbName, collName);
+    const sourceCollectionUUIDString = extractUUIDFromObject(sourceCollectionUUID);
+    return `${dbName}.system.resharding.${sourceCollectionUUIDString}`;
+};
+
+// Callers must ensure the temporary collection has actually been created by the time this is
+// called.
+const getTempUUID = (tempNs) => {
+    const tempCollection = mongos.getCollection(tempNs);
+    return getUUIDFromConfigCollections(mongos, tempCollection.getFullName());
+};
+
+const st = new ShardingTest({
+    mongos: 1,
+    config: 1,
+    shards: 2,
+    rs: {nodes: 2},
+});
+
+const sourceCollection = st.s.getCollection("reshardingDb.coll");
+
+CreateShardedCollectionUtil.shardCollectionWithChunks(sourceCollection, {oldKey: 1}, [
+    {min: {oldKey: MinKey}, max: {oldKey: MaxKey}, shard: st.shard0.shardName},
+]);
+
+const reshardKey = {
+    newKey: 1
+};
+const configsvrReshardCollectionCmd = {
+    _configsvrReshardCollection: sourceCollection.getFullName(),
+    key: reshardKey,
+    writeConcern: {w: "majority"}
+};
+
+// Before starting the actual resharding, get the source collection's UUID to construct the
+// namespace for the temporary collection that will be created.
+const sourceDBName = sourceCollection.getDB();
+const sourceCollName = sourceCollection.getName();
+const tempNs = constructTempReshardingNs(sourceDBName, sourceCollName);
+
+const mongos = sourceCollection.getMongo();
+const topology = DiscoverTopology.findConnectedNodes(mongos);
+const configsvr = new Mongo(topology.configsvr.nodes[0]);
+
+const reshardCollectionThread1 =
+    makeConfigsvrReshardCollectionThread(topology.mongos.nodes[0], configsvrReshardCollectionCmd);
+const pauseBeforeCloningFP =
+    configureFailPoint(configsvr, "reshardingPauseCoordinatorBeforeCloning");
+
+// Issue the first _configsvrReshardCollection command and pause after the temporary collection is
+// created but before its config.collections entry is replaced.
+reshardCollectionThread1.start();
+pauseBeforeCloningFP.wait();
+
+// The UUID of the temporary resharding collection should become the UUID of the original collection
+// once resharding has completed.
+const expectedUUIDAfterReshardingCompletes = getTempUUID(tempNs);
+
+const reshardCollectionJoinedFP =
+    configureFailPoint(configsvr, "reshardCollectionJoinedExistingOperation");
+const reshardCollectionThread2 =
+    makeConfigsvrReshardCollectionThread(topology.mongos.nodes[0], configsvrReshardCollectionCmd);
+
+// Hitting the reshardCollectionJoinedFP is additional confirmation that the second
+// _configsvrReshardCollection command (identical to the first) gets joined with the instance
+// created/running for the first command issued.
+reshardCollectionThread2.start();
+reshardCollectionJoinedFP.wait();
+
+reshardCollectionJoinedFP.off();
+pauseBeforeCloningFP.off();
+
+reshardCollectionThread2.join();
+reshardCollectionThread1.join();
+
+// Confirm the UUID for the namespace that was resharded is the same as the temporary collection's
+// UUID before the second reshardCollection command was issued.
+const finalSourceCollectionUUID = getUUIDFromListCollections(sourceDBName, sourceCollName);
+assert.eq(expectedUUIDAfterReshardingCompletes, finalSourceCollectionUUID);
+
+st.stop();
+})();
diff --git a/jstests/sharding/resharding_on_existing_key_is_noop.js b/jstests/sharding/resharding_on_existing_key_is_noop.js
new file mode 100644
index 00000000000..dcc3f68178e
--- /dev/null
+++ b/jstests/sharding/resharding_on_existing_key_is_noop.js
@@ -0,0 +1,39 @@
+/**
+ * Tests that trying to perform reshardCollection with a resharding key that matches the
+ * collection's existing shard key is a noop (which can be done by confirming the collection's UUID
+ * remains unchanged after the operation).
+ *
+ * @tags: [uses_atclustertime, requires_fcv_49,]
+ */
+(function() {
+"use strict";
+
+load("jstests/libs/uuid_util.js");
+load("jstests/sharding/libs/create_sharded_collection_util.js");
+
+const st = new ShardingTest({
+    mongos: 1,
+    config: 1,
+    shards: 2,
+    rs: {nodes: 2},
+});
+
+const sourceCollection = st.s.getCollection("reshardingDb.coll");
+
+CreateShardedCollectionUtil.shardCollectionWithChunks(sourceCollection, {key: 1}, [
+    {min: {key: MinKey}, max: {key: 0}, shard: st.shard0.shardName},
+    {min: {key: 0}, max: {key: MaxKey}, shard: st.shard1.shardName},
+]);
+
+const ns = sourceCollection.getFullName();
+const mongos = sourceCollection.getMongo();
+const sourceDB = sourceCollection.getDB();
+
+// The UUID should remain the same if the resharding key matches the existing shard key.
+const preReshardCollectionUUID = getUUIDFromListCollections(sourceDB, sourceCollection.getName());
+assert.commandWorked(mongos.adminCommand({reshardCollection: ns, key: {key: 1}}));
+const postReshardCollectionUUID = getUUIDFromListCollections(sourceDB, sourceCollection.getName());
+assert.eq(preReshardCollectionUUID, postReshardCollectionUUID);
+
+st.stop();
+})();