diff --git a/source/dnode/vnode/src/tsdb/tsdbRead2.c b/source/dnode/vnode/src/tsdb/tsdbRead2.c
index ea8801bf1f..ca1ce02210 100644
--- a/source/dnode/vnode/src/tsdb/tsdbRead2.c
+++ b/source/dnode/vnode/src/tsdb/tsdbRead2.c
@@ -76,7 +76,7 @@ static void          updateComposedBlockInfo(STsdbReader* pReader, double el, ST
 
 static bool outOfTimeWindow(int64_t ts, STimeWindow* pWindow) { return (ts > pWindow->ekey) || (ts < pWindow->skey); }
 
-static void resetProcMemTableListIndex(SReaderStatus* pStatus);
+static void resetPreFilesetMemTableListIndex(SReaderStatus* pStatus);
 
 static int32_t setColumnIdSlotList(SBlockLoadSuppInfo* pSupInfo, SColumnInfo* pCols, const int32_t* pSlotIdList,
                                    int32_t numOfCols) {
@@ -2567,9 +2567,9 @@ static void prepareDurationForNextFileSet(STsdbReader* pReader) {
   }
 
   if (pReader->status.bProcMemPreFileset) {
-    uInfo("has mem preset");
+    tsdbDebug("will start pre-fileset %d buffer processing. %s", fid, pReader->idStr);
     pReader->status.procMemUidList.tableUidList = pReader->status.uidList.tableUidList;
-    resetProcMemTableListIndex(&pReader->status);
+    resetPreFilesetMemTableListIndex(&pReader->status);
   }
 
   if (!pReader->status.bProcMemPreFileset) {
@@ -2577,7 +2577,7 @@ static void prepareDurationForNextFileSet(STsdbReader* pReader) {
       STsdReaderNotifyInfo info = {0};
       info.duration.filesetId = fid;
       pReader->notifyFn(TSD_READER_NOTIFY_DURATION_START, &info, pReader->notifyParam);
-      uInfo("new duration notification. %d", fid);
+      tsdbDebug("new duration %d start notification when no buffer preceeding fileset, %s", fid, pReader->idStr);
     }
   }
 
@@ -2648,7 +2648,7 @@ static void resetTableListIndex(SReaderStatus* pStatus) {
   pStatus->pTableIter = tSimpleHashGet(pStatus->pTableMap, &uid, sizeof(uid));
 }
 
-static void resetProcMemTableListIndex(SReaderStatus* pStatus) {
+static void resetPreFilesetMemTableListIndex(SReaderStatus* pStatus) {
   STableUidList* pList = &pStatus->procMemUidList;
 
   pList->currentIndex = 0;
@@ -2668,14 +2668,15 @@ static bool moveToNextTable(STableUidList* pOrderedCheckInfo, SReaderStatus* pSt
   return (pStatus->pTableIter != NULL);
 }
 
-static bool moveToNextTablePreFileSet(STableUidList* pOrderedCheckInfo, SReaderStatus* pStatus) {
-  pOrderedCheckInfo->currentIndex += 1;
-  if (pOrderedCheckInfo->currentIndex >= tSimpleHashGetSize(pStatus->pTableMap)) {
+static bool moveToNextTableForPreFileSetMem(SReaderStatus* pStatus) {
+  STableUidList* pUidList = &pStatus->procMemUidList;
+  pUidList->currentIndex += 1;
+  if (pUidList->currentIndex >= tSimpleHashGetSize(pStatus->pTableMap)) {
     pStatus->pProcMemTableIter = NULL;
     return false;
   }
 
-  uint64_t uid = pOrderedCheckInfo->tableUidList[pOrderedCheckInfo->currentIndex];
+  uint64_t uid = pUidList->tableUidList[pUidList->currentIndex];
   pStatus->pProcMemTableIter = tSimpleHashGet(pStatus->pTableMap, &uid, sizeof(uid));
   return (pStatus->pProcMemTableIter != NULL);
 }
@@ -2914,11 +2915,10 @@ static int32_t doBuildDataBlock(STsdbReader* pReader) {
   return (pReader->code != TSDB_CODE_SUCCESS) ? pReader->code : code;
 }
 
-static int32_t buildBlockFromBufferPreFilesetSequentially(STsdbReader* pReader, int64_t endKey) {
+static int32_t buildBlockFromBufferSeqForPreFileset(STsdbReader* pReader, int64_t endKey) {
   SReaderStatus* pStatus = &pReader->status;
-  STableUidList* pUidList = &pStatus->procMemUidList;
 
-  tsdbDebug("seq load data blocks from cache, %s", pReader->idStr);
+  tsdbDebug("seq load data blocks from cache that preceeds fileset %d, %s", pReader->status.pCurrentFileset->fid, pReader->idStr);
 
   while (1) {
     if (pReader->code != TSDB_CODE_SUCCESS) {
@@ -2929,7 +2929,7 @@ static int32_t buildBlockFromBufferPreFilesetSequentially(STsdbReader* pReader,
     STableBlockScanInfo** pBlockScanInfo = pStatus->pProcMemTableIter;
     if (pReader->pIgnoreTables &&
         taosHashGet(*pReader->pIgnoreTables, &(*pBlockScanInfo)->uid, sizeof((*pBlockScanInfo)->uid))) {
-      bool hasNexTable = moveToNextTablePreFileSet(pUidList, pStatus);
+      bool hasNexTable = moveToNextTableForPreFileSetMem(pStatus);
       if (!hasNexTable) {
         return TSDB_CODE_SUCCESS;
       }
@@ -2949,7 +2949,7 @@ static int32_t buildBlockFromBufferPreFilesetSequentially(STsdbReader* pReader,
     }
 
     // current table is exhausted, let's try next table
-    bool hasNexTable = moveToNextTablePreFileSet(pUidList, pStatus);
+    bool hasNexTable = moveToNextTableForPreFileSetMem(pStatus);
     if (!hasNexTable) {
       return TSDB_CODE_SUCCESS;
     }
@@ -4311,7 +4311,7 @@ _err:
   return code;
 }
 
-static int32_t buildMemoryBlockPreFileset(STsdbReader* pReader) {
+static int32_t buildFromPreFilesetBuffer(STsdbReader* pReader) {
   int32_t code = TSDB_CODE_SUCCESS;
   SReaderStatus* pStatus = &pReader->status;
 
@@ -4322,21 +4322,22 @@ static int32_t buildMemoryBlockPreFileset(STsdbReader* pReader) {
   tsdbFidKeyRange(fid, pReader->pTsdb->keepCfg.days, pReader->pTsdb->keepCfg.precision, &win.skey, &win.ekey);
 
   int64_t endKey = (ASCENDING_TRAVERSE(pReader->info.order)) ? win.skey : win.ekey;
-  code = buildBlockFromBufferPreFilesetSequentially(pReader, endKey);
-  uInfo("zsl mem block rows: %ld", pBlock->info.rows);
+  code = buildBlockFromBufferSeqForPreFileset(pReader, endKey);
   if (code != TSDB_CODE_SUCCESS || pBlock->info.rows > 0) {
     return code;
   } else {
+    tsdbDebug("finished pre-fileset %d buffer processing. %s", fid, pReader->idStr);
     pStatus->bProcMemPreFileset = false;
     if (pReader->notifyFn) {
       STsdReaderNotifyInfo info = {0};
       info.duration.filesetId = fid;
       pReader->notifyFn(TSD_READER_NOTIFY_DURATION_START, &info, pReader->notifyParam);
-      uInfo("new duration notification. mem pre fileset : %d", fid);
+      tsdbDebug("new duration %d start notification when no buffer preceeding fileset, %s", fid, pReader->idStr);
     }
-    if (pStatus->pNextFileBlock && pStatus->pNextFileBlock->info.rows > 0) {
-      copyDataBlock(pBlock, pStatus->pNextFileBlock);
-      blockDataDestroy(pStatus->pNextFileBlock);
+    if (pStatus->pNextFilesetBlock && pStatus->pNextFilesetBlock->info.rows > 0) {
+      tsdbDebug("return the saved block from fileset %d files, %s", fid, pReader->idStr);
+      copyDataBlock(pBlock, pStatus->pNextFilesetBlock);
+      blockDataDestroy(pStatus->pNextFilesetBlock);
     }
   }
   return code;
@@ -4349,7 +4350,7 @@ static int32_t doTsdbNextDataBlockFilesetDelimited(STsdbReader* pReader) {
 
   if (pStatus->loadFromFile) {
     if (pStatus->bProcMemPreFileset) {
-      code = buildMemoryBlockPreFileset(pReader);
+      code = buildFromPreFilesetBuffer(pReader);
       if (code != TSDB_CODE_SUCCESS || pBlock->info.rows > 0) {
         return code;
       }
@@ -4359,18 +4360,16 @@ static int32_t doTsdbNextDataBlockFilesetDelimited(STsdbReader* pReader) {
     if (code != TSDB_CODE_SUCCESS) {
       return code;
     }
+
     if (pStatus->bProcMemPreFileset && pBlock->info.rows > 0) {
-      pStatus->pNextFileBlock = createOneDataBlock(pBlock, true);
+      pStatus->pNextFilesetBlock = createOneDataBlock(pBlock, true);
       blockDataCleanup(pBlock);
-      code = buildMemoryBlockPreFileset(pReader);
+      code = buildFromPreFilesetBuffer(pReader);
       if (code != TSDB_CODE_SUCCESS || pBlock->info.rows > 0) {
         return code;
       }
     }
     
-
-    uInfo("zsl file block rows %ld", pBlock->info.rows);
-
     if (pBlock->info.rows <= 0) {
       resetTableListIndex(&pReader->status);
       int64_t endKey = (ASCENDING_TRAVERSE(pReader->info.order)) ? INT64_MAX : INT64_MIN;
diff --git a/source/dnode/vnode/src/tsdb/tsdbReadUtil.h b/source/dnode/vnode/src/tsdb/tsdbReadUtil.h
index 09ab064806..fe3441d058 100644
--- a/source/dnode/vnode/src/tsdb/tsdbReadUtil.h
+++ b/source/dnode/vnode/src/tsdb/tsdbReadUtil.h
@@ -210,6 +210,8 @@ typedef struct SReaderStatus {
   SArray*               pLDataIterArray;
   SRowMerger            merger;
   SColumnInfoData*      pPrimaryTsCol;  // primary time stamp output col info data
+  // the following for preceeds fileset memory processing 
+  // TODO: refactor into seperate struct
   bool                  bProcMemPreFileset;
   int64_t               memTableMaxKey;
   int64_t               memTableMinKey;
@@ -218,7 +220,7 @@ typedef struct SReaderStatus {
   bool                  bProcMemFirstFileset;
   STableUidList         procMemUidList;
   STableBlockScanInfo** pProcMemTableIter;
-  SSDataBlock*           pNextFileBlock;
+  SSDataBlock*           pNextFilesetBlock;
 } SReaderStatus;
 
 struct STsdbReader {