debug: Added detailed parseMessages logging to identify root cause

Phase 9: Root Cause Identified - Disk Cache Not Updated on Flush

Analysis:
  - Consumer stops at offset 600/601 (pattern repeats at multiples of ~600)
  - Buffer state shows: startOffset=601, bufferStart=602 (data flushed!)
  - Disk read attempts to read offset 601
  - Disk cache contains ONLY offsets 0-100 (first flush)
  - Subsequent flushes (101-150, 151-200, ..., 551-601) NOT in cache

Flush logs confirm regular flushes:
  - offset 51: First flush (0-50)
  - offset 101: Second flush (51-100)
  - offset 151, 201, 251, ..., 602: Subsequent flushes
  - ALL flushes succeed, but cache not updated!

ROOT CAUSE:
  The disk cache (diskChunkCache) is only populated on the FIRST
  flush. Subsequent flushes write to disk successfully, but the
  cache is never updated with the new chunk boundaries.

  When a consumer requests offset 601:
  1. Buffer has flushed, so bufferStart=602
  2. Code correctly tries disk read
  3. Cache has chunk 0-100, returns 'data not on disk'
  4. Code returns empty, consumer stalls

FIX NEEDED:
  Update diskChunkCache after EVERY flush, not just first one.
  OR invalidate cache more aggressively to force fresh reads.

Next: Fix diskChunkCache update in flush logic

weed/util/log_buffer/log_read_stateless.go

@@ -428,6 +428,7 @@ func parseMessagesFromBuffer(buf []byte, startOffset int64, maxMessages int, max
 	totalBytes = 0
 	foundStart := false
 
+	messagesInBuffer := 0
 	for pos := 0; pos+4 < len(buf) && len(messages) < maxMessages && totalBytes < maxBytes; {
 		// Read message size
 		size := util.BytesToUint32(buf[pos : pos+4])
@@ -447,14 +448,18 @@ func parseMessagesFromBuffer(buf []byte, startOffset int64, maxMessages int, max
 			continue
 		}
 
+		messagesInBuffer++
+
 		// Initialize foundStart from first message
 		if !foundStart {
 			// Find the first message at or after startOffset
 			if logEntry.Offset >= startOffset {
+				glog.Infof("[parseMessages] Found first message at/after startOffset %d: logEntry.Offset=%d", startOffset, logEntry.Offset)
 				foundStart = true
 				nextOffset = logEntry.Offset
 			} else {
 				// Skip messages before startOffset
+				glog.V(3).Infof("[parseMessages] Skipping message at offset %d (before startOffset %d)", logEntry.Offset, startOffset)
 				pos += 4 + int(size)
 				continue
 			}
@@ -462,6 +467,7 @@ func parseMessagesFromBuffer(buf []byte, startOffset int64, maxMessages int, max
 
 		// Check if this message matches expected offset
 		if foundStart && logEntry.Offset >= startOffset {
+			glog.V(3).Infof("[parseMessages] Adding message at offset %d (count=%d)", logEntry.Offset, len(messages)+1)
 			messages = append(messages, logEntry)
 			totalBytes += 4 + int(size)
 			nextOffset = logEntry.Offset + 1
@@ -470,6 +476,9 @@ func parseMessagesFromBuffer(buf []byte, startOffset int64, maxMessages int, max
 		pos += 4 + int(size)
 	}
 
+	glog.Infof("[parseMessages] Parsed buffer: requested startOffset=%d, messagesInBuffer=%d, messagesReturned=%d, nextOffset=%d",
+		startOffset, messagesInBuffer, len(messages), nextOffset)
+
 	glog.V(4).Infof("[parseMessages] Parsed %d messages, nextOffset=%d, totalBytes=%d",
 		len(messages), nextOffset, totalBytes)