SERVER-32533 In oplog truncate with WT, don't use a start key.

Previously there was a performance benefit to tracking the first
expected key in the oplog. The performance issue is no longer
relevant, and supplying a key makes the code fragile (if the tracked
key gets out of sync with the real first key).

(cherry picked from commit f4ac177b55bc762e977dc093a40e442b7061f58c)

1 files changed, 14 insertions, 7 deletions

diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
index 5c323bc40f9..4d1d0a8faab 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_record_store.cpp
@@ -1221,15 +1221,22 @@ void WiredTigerRecordStore::reclaimOplog(OperationContext* txn) {
         try {
             WriteUnitOfWork wuow(txn);
 
-            WiredTigerCursor startwrap(_uri, _tableId, true, txn);
-            WT_CURSOR* start = startwrap.get();
-            start->set_key(start, _makeKey(_oplogStones->firstRecord));
+            WiredTigerCursor cwrap(_uri, _tableId, true, txn);
+            WT_CURSOR* cursor = cwrap.get();
 
-            WiredTigerCursor endwrap(_uri, _tableId, true, txn);
-            WT_CURSOR* end = endwrap.get();
-            end->set_key(end, _makeKey(stone->lastRecord));
+            // The first record in the oplog should be within the truncate range.
+            int ret = WT_READ_CHECK(cursor->next(cursor));
+            invariantWTOK(ret);
+            int64_t key;
+            invariantWTOK(cursor->get_key(cursor, &key));
+            RecordId firstRecord = _fromKey(key);
+            if (firstRecord < _oplogStones->firstRecord || firstRecord > stone->lastRecord) {
+                warning() << "First oplog record " << firstRecord << " is not in truncation range ("
+                          << _oplogStones->firstRecord << ", " << stone->lastRecord << ")";
+            }
 
-            invariantWTOK(session->truncate(session, nullptr, start, end, nullptr));
+            cursor->set_key(cursor, _makeKey(stone->lastRecord));
+            invariantWTOK(session->truncate(session, nullptr, nullptr, cursor, nullptr));
             _changeNumRecords(txn, -stone->records);
             _increaseDataSize(txn, -stone->bytes);