Add some comment to log system

and resolve review comment by deleting my questions.

fdbserver/ClusterController.actor.cpp

@@ -2091,6 +2091,7 @@ void registerWorker( RegisterWorkerRequest req, ClusterControllerData *self ) {
 			}
 		}
 	}
+	// Recruit storage cache role. The storage cache project is paused. Its code path is unlikely used.
 	Optional<uint16_t> newStorageCache = req.storageCacheInterf.present() ? req.storageCacheInterf.get().first : Optional<uint16_t>();
 	auto& cacheInfo = self->id_worker[w.locality.processId()].storageCacheInfo;
 	if (req.storageCacheInterf.present()) {

fdbserver/LogRouter.actor.cpp

@@ -235,6 +235,8 @@ ACTOR Future<Void> waitForVersion( LogRouterData *self, Version ver ) {
 	return Void();
 }
 
+// Log router (LR) asynchronously pull data from satellite tLogs (preferred) or primary tLogs at tag (self->routerTag)
+// for the version range from the LR's current version (exclusive) to its epoch's end version or recovery version.
 ACTOR Future<Void> pullAsyncData( LogRouterData *self ) {
 	state Future<Void> dbInfoChange = Void();
 	state Reference<ILogSystem::IPeekCursor> r;

fdbserver/LogSystem.h

@@ -60,7 +60,7 @@ public:
 	Reference<LocalitySet> logServerSet;
 	std::vector<int> logIndexArray;
 	std::vector<LocalityEntry> logEntryArray;
-	bool isLocal;
+	bool isLocal; // true if the LogSet is in primary DC or primary DC's satellite
 	int8_t locality;
 	Version startVersion;
 	std::vector<Future<TLogLockResult>> replies;

fdbserver/TagPartitionedLogSystem.actor.cpp

@@ -949,6 +949,8 @@ struct TagPartitionedLogSystem : ILogSystem, ReferenceCounted<TagPartitionedLogS
 		}
 	}
 
+	// Return a peek cursor that peeks data at tag from the begin version to either the recovery version if peeking at
+	// the latest epoch or the peek cursor's epoch's end version if peeking at an old epoch.
 	Reference<IPeekCursor> peekLogRouter(UID dbgid, Version begin, Tag tag) final {
 		bool found = false;
 		for (const auto& log : tLogs) {

fdbserver/WorkerInterface.actor.h

@@ -214,7 +214,6 @@ struct RecruitFromConfigurationReply {
 	Optional<Key> dcId; // dcId is where master is recruited. It prefers to be in configuration.primaryDcId, but
 	                    // it can be recruited from configuration.secondaryDc: The dcId will be the secondaryDcId and
 	                    // this generation's primaryDC in memory is different from configuration.primaryDcId.
-	                    // when is dcId set?
 	bool satelliteFallback;
 
 	RecruitFromConfigurationReply() : satelliteFallback(false) {}