SERVER-23418 Use globally unique snapshot IDsr3.3.4

2 files changed, 11 insertions, 5 deletions

diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.cpp
index 64ef576378a..da241c5e20e 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.cpp
@@ -44,12 +44,18 @@
 #include "mongo/util/stacktrace.h"
 
 namespace mongo {
+namespace {
+// SnapshotIds need to be globally unique, as they are used in a WorkingSetMember to
+// determine if documents changed, but a different recovery unit may be used across a getMore,
+// so there is a chance the snapshot ID will be reused.
+AtomicUInt64 nextSnapshotId{1};
+}  // namespace
 
 WiredTigerRecoveryUnit::WiredTigerRecoveryUnit(WiredTigerSessionCache* sc)
     : _sessionCache(sc),
       _inUnitOfWork(false),
       _active(false),
-      _myTransactionCount(1),
+      _mySnapshotId(nextSnapshotId.fetchAndAdd(1)),
       _everStartedWrite(false) {}
 
 WiredTigerRecoveryUnit::~WiredTigerRecoveryUnit() {
@@ -61,7 +67,7 @@ void WiredTigerRecoveryUnit::reportState(BSONObjBuilder* b) const {
     b->append("wt_inUnitOfWork", _inUnitOfWork);
     b->append("wt_active", _active);
     b->append("wt_everStartedWrite", _everStartedWrite);
-    b->appendNumber("wt_myTransactionCount", static_cast<long long>(_myTransactionCount));
+    b->appendNumber("wt_mySnapshotId", static_cast<long long>(_mySnapshotId));
     if (_active)
         b->append("wt_millisSinceCommit", _timer.millis());
 }
@@ -206,12 +212,12 @@ void WiredTigerRecoveryUnit::_txnClose(bool commit) {
         LOG(3) << "WT rollback_transaction";
     }
     _active = false;
-    _myTransactionCount++;
+    _mySnapshotId = nextSnapshotId.fetchAndAdd(1);
 }
 
 SnapshotId WiredTigerRecoveryUnit::getSnapshotId() const {
     // TODO: use actual wiredtiger txn id
-    return SnapshotId(_myTransactionCount);
+    return SnapshotId(_mySnapshotId);
 }
 
 Status WiredTigerRecoveryUnit::setReadFromMajorityCommittedSnapshot() {
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.h b/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.h
index 63e49c06c86..cbd6ad955d5 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.h
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_recovery_unit.h
@@ -131,7 +131,7 @@ private:
     bool _areWriteUnitOfWorksBanned = false;
     bool _inUnitOfWork;
     bool _active;
-    uint64_t _myTransactionCount;
+    uint64_t _mySnapshotId;
     bool _everStartedWrite;
     Timer _timer;
     RecordId _oplogReadTill;