SERVER-48452 Internal readers should default to reading without a timestamp

Removes ReadSource::kUnset in favor of kNoTimestamp as the default

Makes the following behavioral changes to AutoGetCollectionForRead:
* Removes special early-return handling for kNoTimestamp
* Only user or DBDirectClient operations are eligible to read at
  kLastApplied.
* Operations only read at kLastApplied when in the SECONDARY state, nothing
  else. This means most internal operations that use DBDirectClient do not need
  to use a ReadSourceScope to ensure they read at kNoTimestamp.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_kv_engine_test.cpp b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_kv_engine_test.cpp
index fcf49f74442..e249daed751 100644
--- a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_kv_engine_test.cpp
+++ b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_kv_engine_test.cpp
@@ -359,7 +359,7 @@ TEST_F(EphemeralForTestKVEngineTest, ReadOlderSnapshotsSimple) {
     ASSERT(!rs->findRecord(&opCtx, loc2, &rd));
 
     opCtx.recoveryUnit()->abandonSnapshot();
-    opCtx.recoveryUnit()->setTimestampReadSource(RecoveryUnit::ReadSource::kUnset);
+    opCtx.recoveryUnit()->setTimestampReadSource(RecoveryUnit::ReadSource::kNoTimestamp);
     ASSERT(rs->findRecord(&opCtx, loc1, &rd));
     ASSERT(rs->findRecord(&opCtx, loc2, &rd));
 }
@@ -452,7 +452,7 @@ TEST_F(EphemeralForTestKVEngineTest, SetReadTimestampBehindOldestTimestamp) {
     ASSERT_THROWS_CODE(rs->findRecord(&opCtx, loc2, &rd), DBException, ErrorCodes::SnapshotTooOld);
 
     opCtx.recoveryUnit()->abandonSnapshot();
-    opCtx.recoveryUnit()->setTimestampReadSource(RecoveryUnit::ReadSource::kUnset);
+    opCtx.recoveryUnit()->setTimestampReadSource(RecoveryUnit::ReadSource::kNoTimestamp);
     ASSERT(rs->findRecord(&opCtx, loc1, &rd));
     ASSERT(rs->findRecord(&opCtx, loc2, &rd));
 }