reuse cached records

weed/mq/kafka/integration/broker_client_subscribe.go

@@ -306,7 +306,24 @@ func (bc *BrokerClient) ReadRecordsFromOffset(ctx context.Context, session *Brok
 		// Update session state after successful seek
 		session.mu.Lock()
 		session.StartOffset = requestedOffset
-		session.consumedRecords = nil // Clear cache after seek
+
+		// CRITICAL: Only clear cache if seeking forward past cached data
+		// For backward seeks, keep cache to avoid re-reading same data from broker
+		shouldClearCache := true
+		if len(session.consumedRecords) > 0 {
+			cacheStartOffset := session.consumedRecords[0].Offset
+			cacheEndOffset := session.consumedRecords[len(session.consumedRecords)-1].Offset
+			// Keep cache if seeking to an offset within or before cached range
+			if requestedOffset <= cacheEndOffset {
+				shouldClearCache = false
+				glog.V(2).Infof("[FETCH] Keeping cache after seek to %d (cache: [%d-%d])",
+					requestedOffset, cacheStartOffset, cacheEndOffset)
+			}
+		}
+		if shouldClearCache {
+			session.consumedRecords = nil
+			glog.V(2).Infof("[FETCH] Cleared cache after forward seek to %d", requestedOffset)
+		}
 		session.mu.Unlock()
 
 		glog.V(2).Infof("[FETCH] Seek to offset %d successful", requestedOffset)
@@ -751,7 +768,17 @@ func (session *BrokerSubscriberSession) SeekToOffset(offset int64) error {
 
 	session.mu.Lock()
 	session.StartOffset = offset
-	session.consumedRecords = nil
+	// Only clear cache if seeking forward past cached data
+	shouldClearCache := true
+	if len(session.consumedRecords) > 0 {
+		cacheEndOffset := session.consumedRecords[len(session.consumedRecords)-1].Offset
+		if offset <= cacheEndOffset {
+			shouldClearCache = false
+		}
+	}
+	if shouldClearCache {
+		session.consumedRecords = nil
+	}
 	session.mu.Unlock()
 
 	glog.V(2).Infof("[SEEK] Seeked to offset %d for %s[%d]", offset, session.Topic, session.Partition)