SERVER-19855 Use ShardConnection for migrations and splits

This ensures that prior to sending the operation on the wire, the host
will be primed to know that it is part of a sharded cluster.

4 files changed, 12 insertions, 14 deletions

diff --git a/src/mongo/s/chunk.cpp b/src/mongo/s/chunk.cpp
index da6cbc196df..23cbf463778 100644
--- a/src/mongo/s/chunk.cpp
+++ b/src/mongo/s/chunk.cpp
@@ -435,8 +435,6 @@ Status Chunk::multiSplit(OperationContext* txn, const vector<BSONObj>& m, BSONOb
     uassert(13333, "can't split a chunk in that many parts", m.size() < maxSplitPoints);
     uassert(13003, "can't split a chunk with only one distinct value", _min.woCompare(_max));
 
-    ScopedDbConnection conn(_getShardConnectionString());
-
     BSONObjBuilder cmd;
     cmd.append("splitChunk", _manager->getns());
     cmd.append("keyPattern", _manager->getShardKeyPattern().toBSON());
@@ -453,6 +451,7 @@ Status Chunk::multiSplit(OperationContext* txn, const vector<BSONObj>& m, BSONOb
         res = &dummy;
     }
 
+    ShardConnection conn(_getShardConnectionString(), "");
     if (!conn->runCommand("admin", cmdObj, *res)) {
         string msg(str::stream() << "splitChunk failed - cmd: " << cmdObj << " result: " << *res);
         warning() << msg;
@@ -481,17 +480,15 @@ bool Chunk::moveAndCommit(OperationContext* txn,
     log() << "moving chunk ns: " << _manager->getns() << " moving ( " << toString() << ") "
           << getShardId() << " -> " << toShardId;
 
-    const auto from = grid.shardRegistry()->getShard(getShardId());
-
     BSONObjBuilder builder;
     builder.append("moveChunk", _manager->getns());
-    builder.append("from", from->getConnString().toString());
+    builder.append("from", _getShardConnectionString().toString());
     {
         const auto toShard = grid.shardRegistry()->getShard(toShardId);
         builder.append("to", toShard->getConnString().toString());
     }
     // NEEDED FOR 2.0 COMPATIBILITY
-    builder.append("fromShard", from->getId());
+    builder.append("fromShard", getShardId());
     builder.append("toShard", toShardId);
     ///////////////////////////////
     builder.append("min", _min);
@@ -515,7 +512,7 @@ bool Chunk::moveAndCommit(OperationContext* txn,
     builder.append(LiteParsedQuery::cmdOptionMaxTimeMS, maxTimeMS);
     builder.append("epoch", _manager->getVersion().epoch());
 
-    ScopedDbConnection fromconn(from->getConnString());
+    ShardConnection fromconn(_getShardConnectionString(), "");
     bool worked = fromconn->runCommand("admin", builder.done(), res);
     fromconn.done();
 
@@ -626,9 +623,9 @@ bool Chunk::splitIfShould(OperationContext* txn, long dataWritten) const {
     }
 }
 
-std::string Chunk::_getShardConnectionString() const {
+ConnectionString Chunk::_getShardConnectionString() const {
     const auto shard = grid.shardRegistry()->getShard(getShardId());
-    return shard->getConnString().toString();
+    return shard->getConnString();
 }
 
 long Chunk::getPhysicalSize() const {
diff --git a/src/mongo/s/chunk.h b/src/mongo/s/chunk.h
index 1ec9a9447cb..822ac534380 100644
--- a/src/mongo/s/chunk.h
+++ b/src/mongo/s/chunk.h
@@ -261,7 +261,7 @@ private:
     /**
      * Returns the connection string for the shard on which this chunk resides.
      */
-    std::string _getShardConnectionString() const;
+    ConnectionString _getShardConnectionString() const;
 
     // if min/max key is pos/neg infinity
     bool _minIsInf() const;
diff --git a/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp b/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp
index 2c3802a8f3b..084b63661f3 100644
--- a/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp
+++ b/src/mongo/s/commands/cluster_merge_chunks_cmd.cpp
@@ -38,6 +38,7 @@
 #include "mongo/s/catalog/catalog_cache.h"
 #include "mongo/s/catalog/catalog_manager.h"
 #include "mongo/s/chunk_manager.h"
+#include "mongo/s/client/shard_connection.h"
 #include "mongo/s/client/shard_registry.h"
 #include "mongo/s/config.h"
 #include "mongo/s/grid.h"
@@ -179,6 +180,7 @@ public:
                              grid.shardRegistry()->getConfigServerConnectionString().toString());
         remoteCmdObjB.append(ClusterMergeChunksCommand::shardNameField(), firstChunk->getShardId());
 
+
         BSONObj remoteResult;
 
         // Throws, but handled at level above.  Don't want to rewrap to preserve exception
@@ -191,7 +193,7 @@ public:
                        str::stream() << "Can't find shard for chunk: " << firstChunk->toString()));
         }
 
-        ScopedDbConnection conn(shard->getConnString());
+        ShardConnection conn(shard->getConnString(), "");
         bool ok = conn->runCommand("admin", remoteCmdObjB.obj(), remoteResult);
         conn.done();
 
diff --git a/src/mongo/s/d_migrate.cpp b/src/mongo/s/d_migrate.cpp
index 269a6d5a5e7..4138c2242a9 100644
--- a/src/mongo/s/d_migrate.cpp
+++ b/src/mongo/s/d_migrate.cpp
@@ -573,7 +573,6 @@ public:
                 return false;
             }
 
-            ScopedDbConnection connTo(toShardCS);
             BSONObj res;
             bool ok;
 
@@ -596,7 +595,9 @@ public:
             }
 
             try {
+                ScopedDbConnection connTo(toShardCS);
                 ok = connTo->runCommand("admin", recvChunkStartBuilder.done(), res);
+                connTo.done();
             } catch (DBException& e) {
                 errmsg = str::stream() << "moveChunk could not contact to: shard " << toShardName
                                        << " to start transfer" << causedBy(e);
@@ -604,8 +605,6 @@ public:
                 return false;
             }
 
-            connTo.done();
-
             if (!ok) {
                 errmsg = "moveChunk failed to engage TO-shard in the data transfer: ";
                 verify(res["errmsg"].type());