Revert "SERVER-39870: Guarantee the oldest timestamp obeys any initial data timestamp constraints."

This reverts commit ef38b62f0de257cfa0c5a2940c67949b7402079b.

1 files changed, 8 insertions, 7 deletions

diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
index b4196565db7..1655591d191 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
@@ -1633,13 +1633,14 @@ void WiredTigerKVEngine::setOldestTimestampFromStable() {
         return;
     }
 
-    const Timestamp initDataTs = getInitialDataTimestamp();
-    if (!initDataTs.isNull() && newOldestTimestamp < initDataTs) {
-        // The oldest timestamp is used to tell WT how much history to keep as well as to guard
-        // readers from reading at too early of a timestamp. Readers may not read at a timestamp
-        // prior to the initial data timestamp. Data is not guaranteed to be consistent at that
-        // time.
-        newOldestTimestamp = initDataTs;
+    const auto oplogReadTimestamp = Timestamp(_oplogManager->getOplogReadTimestamp());
+    if (!oplogReadTimestamp.isNull() && newOldestTimestamp > oplogReadTimestamp) {
+        // Oplog visibility is updated asynchronously from replication updating the commit point.
+        // When force is not set, lag the `oldest_timestamp` to the possibly stale oplog read
+        // timestamp value. This guarantees an oplog reader's `read_timestamp` can always
+        // be serviced. When force is set, we respect the caller's request and do not lag the
+        // oldest timestamp.
+        newOldestTimestamp = oplogReadTimestamp;
     }
 
     setOldestTimestamp(newOldestTimestamp, false);