SERVER-9022 allow releasing sharded conn back to pool after read operation

4 files changed, 49 insertions, 3 deletions

diff --git a/src/mongo/db/dbcommands_generic.cpp b/src/mongo/db/dbcommands_generic.cpp
index ff128dbd1ff..0c842328993 100644
--- a/src/mongo/db/dbcommands_generic.cpp
+++ b/src/mongo/db/dbcommands_generic.cpp
@@ -41,6 +41,7 @@
 #include "../util/version.h"
 #include "../util/ramlog.h"
 #include "repl/multicmd.h"
+#include "mongo/s/shard.h"
 #include "server.h"
 
 namespace mongo {
@@ -165,6 +166,10 @@ namespace mongo {
             if (all || cmdObj.hasElement("replIndexPrefetch")) {
                 result.append("replIndexPrefetch", fetchReplIndexPrefetchParam());
             }
+            if (all || cmdObj.hasElement("releaseConnectionsAfterResponse")) {
+                result.append("releaseConnectionsAfterResponse", 
+                              ShardConnection::releaseConnectionsAfterResponse);
+            }
             if ( before == result.len() ) {
                 errmsg = "no option found to get";
                 return false;
@@ -254,6 +259,15 @@ namespace mongo {
                         cmdObj["replMonitorMaxFailedChecks"].numberInt() );
                 s++;
             }
+            if( cmdObj.hasElement( "releaseConnectionsAfterResponse" ) ) {
+                if ( s == 0 ) {
+                    result.append( "was", 
+                                   ShardConnection::releaseConnectionsAfterResponse );
+                }
+                ShardConnection::releaseConnectionsAfterResponse = 
+                    cmdObj["releaseConnectionsAfterResponse"].trueValue();
+                s++;
+            }
 
             if( s == 0 && !found ) {
                 errmsg = "no option found to set, use help:true to see options ";
diff --git a/src/mongo/s/server.cpp b/src/mongo/s/server.cpp
index e7a963078c1..065069d5a3a 100644
--- a/src/mongo/s/server.cpp
+++ b/src/mongo/s/server.cpp
@@ -102,6 +102,12 @@ namespace mongo {
             try {
                 r.init();
                 r.process();
+
+                // Release connections after non-write op 
+                if ( ShardConnection::releaseConnectionsAfterResponse && r.expectResponse() ) {
+                    LOG(2) << "release thread local connections back to pool" << endl;
+                    ShardConnection::releaseMyConnections();
+                }
             }
             catch ( AssertionException & e ) {
                 LOG( e.isUserAssertion() ? 1 : 0 ) << "AssertionException while processing op type : " << m.operation() << " to : " << r.getns() << causedBy(e) << endl;
diff --git a/src/mongo/s/shard.h b/src/mongo/s/shard.h
index ccb76a923a0..e2d5b2ab980 100644
--- a/src/mongo/s/shard.h
+++ b/src/mongo/s/shard.h
@@ -284,6 +284,18 @@ namespace mongo {
         /** checks all of my thread local connections for the version of this ns */
         static void checkMyConnectionVersions( const string & ns );
 
+        /**
+         * Whether or not we should release all connections after an operation with
+         * a response.
+         */
+        static bool releaseConnectionsAfterResponse;
+
+        /**
+         * Returns all the current sharded connections to the pool.
+         * Note: This is *dangerous* if we have GLE state.
+         */
+        static void releaseMyConnections();
+
     private:
         void _init();
         void _finishInit();
diff --git a/src/mongo/s/shardconnection.cpp b/src/mongo/s/shardconnection.cpp
index 325ad5f3776..0c884b7f764 100644
--- a/src/mongo/s/shardconnection.cpp
+++ b/src/mongo/s/shardconnection.cpp
@@ -116,7 +116,15 @@ namespace mongo {
             // Stop tracking these client connections
             activeClientConnections.remove( this );
 
-            // No longer need spinlock protection
+            releaseAll( true );
+        }
+
+        void releaseAll( bool fromDestructor = false ) {
+
+            // Don't need spinlock protection because if not in the destructor, we don't 
+            // modify _hosts, and if in the destructor we are not accessible to external
+            // threads.
+
             for ( HostMap::iterator i=_hosts.begin(); i!=_hosts.end(); ++i ) {
                 string addr = i->first;
                 Status* ss = i->second;
@@ -132,9 +140,9 @@ namespace mongo {
                         release( addr , ss->avail );
                     ss->avail = 0;
                 }
-                delete ss;
+                if ( fromDestructor ) delete ss;
             }
-            _hosts.clear();
+            if ( fromDestructor ) _hosts.clear();
         }
 
         DBClientBase * get( const string& addr , const string& ns ) {
@@ -372,6 +380,12 @@ namespace mongo {
         ClientConnections::threadInstance()->checkVersions( ns );
     }
 
+    bool ShardConnection::releaseConnectionsAfterResponse( false );
+
+    void ShardConnection::releaseMyConnections() {
+        ClientConnections::threadInstance()->releaseAll();
+    }
+
     ShardConnection::~ShardConnection() {
         if ( _conn ) {
             if ( ! _conn->isFailed() ) {