SERVER-20213 ReIndex must make majority reads wait for complete visibility

2 files changed, 20 insertions, 3 deletions

diff --git a/jstests/noPassthrough/read_majority.js b/jstests/noPassthrough/read_majority.js
index 14d3ae38226..64f287590aa 100644
--- a/jstests/noPassthrough/read_majority.js
+++ b/jstests/noPassthrough/read_majority.js
@@ -117,6 +117,14 @@ assertNoReadMajoritySnapshotAvailable();
 assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot6}));
 assert.eq(getReadMajorityCursor().itcount(), 10);
 
+// Reindex bumps the min snapshot.
+t.reIndex();
+assertNoReadMajoritySnapshotAvailable();
+var snapshot7 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
+assertNoReadMajoritySnapshotAvailable();
+assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot7}));
+assert.eq(getReadMajorityCursor().itcount(), 10);
+
 // Dropping the collection is visible in the committed snapshot, even though it hasn't been marked
 // committed yet. This is allowed by the current specification even though it violates strict
 // read-committed semantics since we don't guarantee them on metadata operations.
@@ -125,11 +133,11 @@ assert.eq(getReadMajorityCursor().itcount(), 0);
 
 // Creating a new collection with the same name hides the collection until that operation is in the
 // committed view.
-t.insert({_id:0, version: 7});
+t.insert({_id:0, version: 8});
 assertNoReadMajoritySnapshotAvailable();
-var snapshot7 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
+var snapshot8 = assert.commandWorked(db.adminCommand("makeSnapshot")).name;
 assertNoReadMajoritySnapshotAvailable();
-assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot7}));
+assert.commandWorked(db.adminCommand({"setCommittedSnapshot": snapshot8}));
 assert.eq(getReadMajorityCursor().itcount(), 1);
 
 MongoRunner.stopMongod(testServer);
diff --git a/src/mongo/db/commands/drop_indexes.cpp b/src/mongo/db/commands/drop_indexes.cpp
index d0e6ac633a5..96757af0834 100644
--- a/src/mongo/db/commands/drop_indexes.cpp
+++ b/src/mongo/db/commands/drop_indexes.cpp
@@ -191,6 +191,15 @@ public:
             wunit.commit();
         }
 
+        // Do not allow majority reads from this collection until all original indexes are visible.
+        // This was also done when dropAllIndexes() committed, but we need to ensure that no one
+        // tries to read in the intermediate state where all indexes are newer than the current
+        // snapshot so are unable to be used.
+        auto replCoord = repl::ReplicationCoordinator::get(txn);
+        auto snapshotName = replCoord->reserveSnapshotName(txn);
+        replCoord->forceSnapshotCreation();  // Ensures a newer snapshot gets created even if idle.
+        collection->setMinimumVisibleSnapshot(snapshotName);
+
         result.append("nIndexes", (int)all.size());
         result.append("indexes", all);