allow majority to be all nodes SERVER-3672

4 files changed, 83 insertions, 13 deletions

diff --git a/db/repl/rs_config.cpp b/db/repl/rs_config.cpp
index 13352b19783..c451d468105 100644
--- a/db/repl/rs_config.cpp
+++ b/db/repl/rs_config.cpp
@@ -296,6 +296,26 @@ namespace mongo {
         _ok = false;
     }
 
+    void ReplSetConfig::setMajority() {
+        int total = members.size();
+        int nonArbiters = total;
+        int strictMajority = total/2+1;
+
+        for (vector<MemberCfg>::iterator it = members.begin(); it < members.end(); it++) {
+            if ((*it).arbiterOnly) {
+                nonArbiters--;
+            }
+        }
+
+        // majority should be all "normal" members if we have something like 4
+        // arbiters & 3 normal members
+        _majority = (strictMajority > nonArbiters) ? nonArbiters : strictMajority;
+    }
+
+    int ReplSetConfig::getMajority() const {
+        return _majority;
+    }
+
     void ReplSetConfig::checkRsConfig() const {
         uassert(13132,
                 "nonmatching repl set name in _id field; check --replSet command line",
@@ -533,6 +553,9 @@ namespace mongo {
             try { getLastErrorDefaults = settings["getLastErrorDefaults"].Obj().copy(); }
             catch(...) { }
         }
+
+        // figure out the majority for this config
+        setMajority();
     }
 
     static inline void configAssert(bool expr) {
diff --git a/db/repl/rs_config.h b/db/repl/rs_config.h
index b22b61e5318..da6552a0d27 100644
--- a/db/repl/rs_config.h
+++ b/db/repl/rs_config.h
@@ -135,9 +135,20 @@ namespace mongo {
 
         BSONObj asBson() const;
 
+        /**
+         * Getter and setter for _majority. This is almost always
+         * members.size()/2+1, but can be the number of non-arbiter members if
+         * there are more arbiters than non-arbiters (writing to 3 out of 7
+         * servers is safe if 4 of the servers are arbiters).
+         */
+        void setMajority();
+        int getMajority() const;
+
         bool _constructed;
     private:
         bool _ok;
+        int _majority;
+
         void from(BSONObj);
         void clear();
 
diff --git a/db/repl_block.cpp b/db/repl_block.cpp
index dcac1218199..840bbb2730e 100644
--- a/db/repl_block.cpp
+++ b/db/repl_block.cpp
@@ -175,7 +175,7 @@ namespace mongo {
             if (wStr == "majority") {
                 // use the entire set, including arbiters, to prevent writing
                 // to a majority of the set but not a majority of voters
-                return replicatedToNum(op, theReplSet->config().members.size()/2+1);
+                return replicatedToNum(op, theReplSet->config().getMajority());
             }
 
             map<string,ReplSetConfig::TagRule*>::const_iterator it = theReplSet->config().rules.find(wStr);
diff --git a/jstests/replsets/majority.js b/jstests/replsets/majority.js
index 6df1a41c694..5bb3cde33f0 100644
--- a/jstests/replsets/majority.js
+++ b/jstests/replsets/majority.js
@@ -1,4 +1,11 @@
-var num = 5;
+var testInsert = function() {
+    master.getDB("foo").bar.insert({x:1});
+    var result = master.getDB("foo").runCommand({getLastError:1, w:"majority", wtimeout:timeout});
+    printjson(result);
+    return result;
+};
+
+var num = 7;
 var host = getHostName();
 var name = "tags";
 var timeout = 10000;
@@ -6,28 +13,57 @@ var timeout = 10000;
 var replTest = new ReplSetTest( {name: name, nodes: num, startPort:31000} );
 var nodes = replTest.startSet();
 var port = replTest.ports;
-replTest.initiate({_id : name, members :
+var config = {_id : name, members :
         [
          {_id:0, host : host+":"+port[0], priority : 2},
-         {_id:1, host : host+":"+port[1]},
+         {_id:1, host : host+":"+port[1], votes : 3},
          {_id:2, host : host+":"+port[2]},
          {_id:3, host : host+":"+port[3], arbiterOnly : true},
          {_id:4, host : host+":"+port[4], arbiterOnly : true},
+         {_id:5, host : host+":"+port[5], arbiterOnly : true},
+         {_id:6, host : host+":"+port[6], arbiterOnly : true},
         ],
-                  });
+             };
+replTest.initiate(config);
 
 replTest.awaitReplication();
-replTest.bridge();
-
-var testInsert = function() {
-    master.getDB("foo").bar.insert({x:1});
-    var result = master.getDB("foo").runCommand({getLastError:1, w:"majority", wtimeout:timeout});
-    printjson(result);
-    return result;
-};
 
 var master = replTest.getMaster();
 
+print("try taking down 4 arbiters");
+replTest.stop(3);
+replTest.stop(4);
+
+replTest.stop(6);
+replTest.remove(6);
+replTest.stop(5);
+replTest.remove(5);
+
+print("should still be able to write to a majority");
+assert.eq(testInsert().err, null);
+
+print("start up some of the arbiters again");
+replTest.restart(3);
+replTest.restart(4);
+
+print("remove 2 of the arbiters");
+config.version = 2;
+config.members.pop();
+config.members.pop();
+
+try {
+    master.getDB("admin").runCommand({replSetReconfig : config});
+}
+catch (e) {
+    print("reconfig error: "+e);
+}
+
+replTest.awaitReplication();
+
+replTest.bridge();
+
+master = replTest.getMaster();
+
 print("get back in the groove");
 testInsert();
 replTest.awaitReplication();