SERVER-29423 Prevent the balancer policy from scheduling migrations with the same source or destination

1 files changed, 54 insertions, 44 deletions

diff --git a/jstests/sharding/auto_rebalance_parallel.js b/jstests/sharding/auto_rebalance_parallel.js
index 4971fc19f7f..c7078a6898a 100644
--- a/jstests/sharding/auto_rebalance_parallel.js
+++ b/jstests/sharding/auto_rebalance_parallel.js
@@ -1,61 +1,71 @@
 /**
  * Tests that the cluster is balanced in parallel in one balancer round (standalone).
  */
+
 (function() {
     'use strict';
 
     var st = new ShardingTest({shards: 4});
+    var config = st.s0.getDB('config');
 
     assert.commandWorked(st.s0.adminCommand({enableSharding: 'TestDB'}));
     st.ensurePrimaryShard('TestDB', st.shard0.shardName);
-    assert.commandWorked(st.s0.adminCommand({shardCollection: 'TestDB.TestColl', key: {Key: 1}}));
-
-    var coll = st.s0.getDB('TestDB').TestColl;
-
-    // Create 4 chunks initially and ensure they get balanced within 1 balancer round
-    assert.writeOK(coll.insert({Key: 1, Value: 'Test value 1'}));
-    assert.writeOK(coll.insert({Key: 10, Value: 'Test value 10'}));
-    assert.writeOK(coll.insert({Key: 20, Value: 'Test value 20'}));
-    assert.writeOK(coll.insert({Key: 30, Value: 'Test value 30'}));
-
-    assert.commandWorked(st.splitAt('TestDB.TestColl', {Key: 10}));
-    assert.commandWorked(st.splitAt('TestDB.TestColl', {Key: 20}));
-    assert.commandWorked(st.splitAt('TestDB.TestColl', {Key: 30}));
-
-    // Move two of the chunks to shard0001 so we have option to do parallel balancing
-    assert.commandWorked(st.moveChunk('TestDB.TestColl', {Key: 20}, st.shard1.shardName));
-    assert.commandWorked(st.moveChunk('TestDB.TestColl', {Key: 30}, st.shard1.shardName));
-
-    assert.eq(2,
-              st.s0.getDB('config')
-                  .chunks.find({ns: "TestDB.TestColl", shard: st.shard0.shardName})
-                  .itcount());
-    assert.eq(2,
-              st.s0.getDB('config')
-                  .chunks.find({ns: "TestDB.TestColl", shard: st.shard1.shardName})
-                  .itcount());
-
-    // Do enable the balancer and wait for a single balancer round
+
+    function prepareCollectionForBalance(collName) {
+        assert.commandWorked(st.s0.adminCommand({shardCollection: collName, key: {Key: 1}}));
+
+        var coll = st.s0.getCollection(collName);
+
+        // Create 4 chunks initially and ensure they get balanced within 1 balancer round
+        assert.writeOK(coll.insert({Key: 1, Value: 'Test value 1'}));
+        assert.writeOK(coll.insert({Key: 10, Value: 'Test value 10'}));
+        assert.writeOK(coll.insert({Key: 20, Value: 'Test value 20'}));
+        assert.writeOK(coll.insert({Key: 30, Value: 'Test value 30'}));
+
+        assert.commandWorked(st.splitAt(collName, {Key: 10}));
+        assert.commandWorked(st.splitAt(collName, {Key: 20}));
+        assert.commandWorked(st.splitAt(collName, {Key: 30}));
+
+        // Move two of the chunks to shard0001 so we have option to do parallel balancing
+        assert.commandWorked(st.moveChunk(collName, {Key: 20}, st.shard1.shardName));
+        assert.commandWorked(st.moveChunk(collName, {Key: 30}, st.shard1.shardName));
+
+        assert.eq(2, config.chunks.find({ns: collName, shard: st.shard0.shardName}).itcount());
+        assert.eq(2, config.chunks.find({ns: collName, shard: st.shard1.shardName}).itcount());
+    }
+
+    function checkCollectionBalanced(collName) {
+        assert.eq(1, config.chunks.find({ns: collName, shard: st.shard0.shardName}).itcount());
+        assert.eq(1, config.chunks.find({ns: collName, shard: st.shard1.shardName}).itcount());
+        assert.eq(1, config.chunks.find({ns: collName, shard: st.shard2.shardName}).itcount());
+        assert.eq(1, config.chunks.find({ns: collName, shard: st.shard3.shardName}).itcount());
+    }
+
+    function countMoves(collName) {
+        return config.changelog.find({what: 'moveChunk.start', ns: collName}).itcount();
+    }
+
+    prepareCollectionForBalance('TestDB.TestColl1');
+    prepareCollectionForBalance('TestDB.TestColl2');
+
+    // Count the moveChunk start attempts accurately and ensure that only the correct number of
+    // migrations are scheduled
+    const testColl1InitialMoves = countMoves('TestDB.TestColl1');
+    const testColl2InitialMoves = countMoves('TestDB.TestColl2');
+
     st.startBalancer();
     st.awaitBalancerRound();
+    st.awaitBalancerRound();
     st.stopBalancer();
 
-    assert.eq(1,
-              st.s0.getDB('config')
-                  .chunks.find({ns: 'TestDB.TestColl', shard: st.shard0.shardName})
-                  .itcount());
-    assert.eq(1,
-              st.s0.getDB('config')
-                  .chunks.find({ns: 'TestDB.TestColl', shard: st.shard1.shardName})
-                  .itcount());
-    assert.eq(1,
-              st.s0.getDB('config')
-                  .chunks.find({ns: 'TestDB.TestColl', shard: st.shard2.shardName})
-                  .itcount());
-    assert.eq(1,
-              st.s0.getDB('config')
-                  .chunks.find({ns: 'TestDB.TestColl', shard: st.shard3.shardName})
-                  .itcount());
+    checkCollectionBalanced('TestDB.TestColl1');
+    checkCollectionBalanced('TestDB.TestColl2');
+
+    assert.eq(2, countMoves('TestDB.TestColl1') - testColl1InitialMoves);
+    assert.eq(2, countMoves('TestDB.TestColl2') - testColl2InitialMoves);
+
+    // Ensure there are no migration errors reported
+    assert.eq(0, config.changelog.find({what: 'moveChunk.error'}).itcount());
 
     st.stop();
 })();