Update vendorized version of dsync that relaxes read quorum to N/2 (#2874)

vendor/github.com/minio/dsync/drwmutex.go

@@ -211,7 +211,8 @@ func lock(clnts []RPC, locks *[]string, lockName string, isReadLock bool) bool {
 					(*locks)[grant.index] = grant.lockUid
 				} else {
 					locksFailed++
-					if locksFailed > dnodeCount-dquorum {
+					if !isReadLock && locksFailed > dnodeCount-dquorum ||
+						isReadLock && locksFailed > dnodeCount-dquorumReads {
 						// We know that we are not going to get the lock anymore, so exit out
 						// and release any locks that did get acquired
 						done = true
@@ -223,7 +224,7 @@ func lock(clnts []RPC, locks *[]string, lockName string, isReadLock bool) bool {
 				done = true
 				// timeout happened, maybe one of the nodes is slow, count
 				// number of locks to check whether we have quorum or not
-				if !quorumMet(locks) {
+				if !quorumMet(locks, isReadLock) {
 					releaseAll(clnts, locks, lockName, isReadLock)
 				}
 			}
@@ -234,7 +235,7 @@ func lock(clnts []RPC, locks *[]string, lockName string, isReadLock bool) bool {
 		}
 
 		// Count locks in order to determine whterh we have quorum or not
-		quorum = quorumMet(locks)
+		quorum = quorumMet(locks, isReadLock)
 
 		// Signal that we have the quorum
 		wg.Done()
@@ -263,8 +264,8 @@ func lock(clnts []RPC, locks *[]string, lockName string, isReadLock bool) bool {
 	return quorum
 }
 
-// quorumMet determines whether we have acquired n/2+1 underlying locks or not
+// quorumMet determines whether we have acquired the required quorum of underlying locks or not
-func quorumMet(locks *[]string) bool {
+func quorumMet(locks *[]string, isReadLock bool) bool {
 
 	count := 0
 	for _, uid := range *locks {
@@ -273,7 +274,11 @@ func quorumMet(locks *[]string) bool {
 		}
 	}
 
-	return count >= dquorum
+	if isReadLock {
+		return count >= dquorumReads
+	} else {
+		return count >= dquorum
+	}
 }
 
 // releaseAll releases all locks that are marked as locked

vendor/github.com/minio/dsync/dsync.go

@@ -34,6 +34,8 @@ var ownNode int
 
 // Simple majority based quorum, set to dNodeCount/2+1
 var dquorum int
+// Simple quorum for read operations, set to dNodeCount/2
+var dquorumReads int
 
 // SetNodesWithPath - initializes package-level global state variables such as clnts.
 // N B - This function should be called only once inside any program that uses
@@ -47,15 +49,17 @@ func SetNodesWithClients(rpcClnts []RPC, rpcOwnNode int) (err error) {
 		return errors.New("Dsync not designed for less than 4 nodes")
 	} else if len(rpcClnts) > 16 {
 		return errors.New("Dsync not designed for more than 16 nodes")
+	} else if len(rpcClnts)&1 == 1 {
+		return errors.New("Dsync not designed for an uneven number of nodes")
 	}
 
 	if rpcOwnNode > len(rpcClnts) {
 		return errors.New("Index for own node is too large")
 	}
 
-
 	dnodeCount = len(rpcClnts)
 	dquorum = dnodeCount/2 + 1
+	dquorumReads = dnodeCount/2
 	// Initialize node name and rpc path for each RPCClient object.
 	clnts = make([]RPC, dnodeCount)
 	copy(clnts, rpcClnts)

vendor/vendor.json

@@ -111,10 +111,10 @@
 			"revisionTime": "2015-11-18T20:00:48-08:00"
 		},
 		{
-			"checksumSHA1": "0wc4gxRamjyjVSiZF73KIaCRC6k=",
+			"checksumSHA1": "5DKBTLXf5GY5RkVC9DGP2XFMabc=",
 			"path": "github.com/minio/dsync",
-			"revision": "531818cd6458e24e30eec2c67136a8bcb24520af",
+			"revision": "66c2a42bf14fcaad0322e9f06d9ab85dd6dba9b7",
-			"revisionTime": "2016-09-15T18:37:01Z"
+			"revisionTime": "2016-10-07T07:30:36Z"
 		},
 		{
 			"path": "github.com/minio/go-homedir",