Do not make extra ZK RTTs in inserts. [#CLICKHOUSE-3]

Resolves #2054

dbms/src/Storages/MergeTree/AbandonableLockInZooKeeper.h

@@ -108,6 +108,12 @@ public:
         ops.emplace_back(std::make_shared<zkutil::Op::Remove>(holder_path, -1));
     }
 
+    /// Do not delete nodes in destructor
+    void setIsUnlocked()
+    {
+        holder_path = "";
+    }
+
     void checkCreated() const
     {
         if (!isCreated())

dbms/src/Storages/MergeTree/ReplicatedMergeTreeBlockOutputStream.cpp

@@ -370,6 +370,9 @@ void ReplicatedMergeTreeBlockOutputStream::commitPart(zkutil::ZooKeeperPtr & zoo
     {
         transaction.commit();
         storage.merge_selecting_event.set();
+
+        /// Lock nodes have been already deleted, do not delete them in destructor
+        block_number_lock.setIsUnlocked();
     }
     else if (zkutil::isUserError(info.code))
     {