diff --git a/src/common/inc/dataformat.h b/src/common/inc/dataformat.h
index 4e8afd4f0eec26b42842fd4b4ddfcff05d876a13..04fa7dcc7dd5e1cb8498b4fa4eb033dfcc92e7c3 100644
--- a/src/common/inc/dataformat.h
+++ b/src/common/inc/dataformat.h
@@ -110,7 +110,8 @@ typedef struct SDataCol {
   int     bytes;
   int     len;
   int     offset;
-  void *  pData;
+  void *  pData; // Original data
+  void *  pCData; // Compressed data
 } SDataCol;
 
 typedef struct {
diff --git a/src/common/src/dataformat.c b/src/common/src/dataformat.c
index 436426c86b5a3279587cb71e3f7b60bdbb2bc271..bff041df1b98c955b67bf9e8a44fa360362908f4 100644
--- a/src/common/src/dataformat.c
+++ b/src/common/src/dataformat.c
@@ -317,14 +317,17 @@ void tdInitDataCols(SDataCols *pCols, STSchema *pSchema) {
   pCols->numOfCols = schemaNCols(pSchema);
 
   pCols->cols[0].pData = pCols->buf;
+  int offset = TD_DATA_ROW_HEAD_SIZE;
   for (int i = 0; i < schemaNCols(pSchema); i++) {
     if (i > 0) {
       pCols->cols[i].pData = (char *)(pCols->cols[i - 1].pData) + schemaColAt(pSchema, i - 1)->bytes * pCols->maxPoints;
     }
     pCols->cols[i].type = colType(schemaColAt(pSchema, i));
     pCols->cols[i].bytes = colBytes(schemaColAt(pSchema, i));
-    pCols->cols[i].offset = colOffset(schemaColAt(pSchema, i));
+    pCols->cols[i].offset = offset;
     pCols->cols[i].colId = colColId(schemaColAt(pSchema, i));
+
+    offset += TYPE_BYTES[pCols->cols[i].type];
   }
 }
 
@@ -343,7 +346,6 @@ void tdResetDataCols(SDataCols *pCols) {
 }
 
 void tdAppendDataRowToDataCol(SDataRow row, SDataCols *pCols) {
-  TSKEY key = dataRowKey(row);
   for (int i = 0; i < pCols->numOfCols; i++) {
     SDataCol *pCol = pCols->cols + i;
     memcpy((void *)((char *)(pCol->pData) + pCol->len), dataRowAt(row, pCol->offset), pCol->bytes);
@@ -379,3 +381,7 @@ static int tdFLenFromSchema(STSchema *pSchema) {
 
   return ret;
 }
+
+int tdMergeDataCols(SDataCols *target, SDataCols *source) {
+  return 0;
+}
\ No newline at end of file
diff --git a/src/os/linux/inc/os.h b/src/os/linux/inc/os.h
index d3c401e3cfc3d4e6ee1d1ebca4baa6b7752355ba..ee75e1a0795323e83ed90243beb9f8ff11738485 100644
--- a/src/os/linux/inc/os.h
+++ b/src/os/linux/inc/os.h
@@ -205,6 +205,8 @@ ssize_t tsendfile(int dfd, int sfd, off_t *offset, size_t size);
 
 ssize_t twrite(int fd, void *buf, size_t n);
 
+ssize_t tread(int fd, void *buf, size_t count);
+
 bool taosCheckPthreadValid(pthread_t thread);
 
 void taosResetPthread(pthread_t *thread);
diff --git a/src/os/linux/src/tlinux.c b/src/os/linux/src/tlinux.c
index 780e2903a064c45211ea3877c3fb2fef3a6c8bef..b819514be7299b73158b3ff7e9dbc07f4109ea76 100644
--- a/src/os/linux/src/tlinux.c
+++ b/src/os/linux/src/tlinux.c
@@ -291,6 +291,30 @@ int taosInitTimer(void (*callback)(int), int ms) {
   return 0;
 }
 
+ssize_t tread(int fd, void *buf, size_t count) {
+  size_t  leftbytes = count;
+  ssize_t readbytes;
+  char *  tbuf = (char *)buf;
+
+  while (leftbytes > 0) {
+    readbytes = read(fd, (void *)tbuf, leftbytes);
+    if (readbytes < 0) {
+      if (errno == EINTR) {
+        continue;
+      } else {
+        return -1;
+      }
+    } else if (readbytes == 0) {
+      return (ssize_t)(count - leftbytes);
+    }
+
+    leftbytes -= readbytes;
+    tbuf += readbytes;
+  }
+
+  return (ssize_t)count;
+}
+
 ssize_t tsendfile(int dfd, int sfd, off_t *offset, size_t size) {
   size_t  leftbytes = size;
   ssize_t sentbytes;
@@ -308,6 +332,8 @@ ssize_t tsendfile(int dfd, int sfd, off_t *offset, size_t size) {
       else {
         return -1;
       }
+    } else if (sentbytes == 0) {
+      return (ssize_t)(size - leftbytes);
     }
 
     leftbytes -= sentbytes;
diff --git a/src/vnode/main/src/vnodeMain.c b/src/vnode/main/src/vnodeMain.c
index 1be9bbb64be2807c3c44d3ca83d789b82f563bb7..ea1859729e55ab4ca35e0aa86461164afa7feb51 100644
--- a/src/vnode/main/src/vnodeMain.c
+++ b/src/vnode/main/src/vnodeMain.c
@@ -32,6 +32,7 @@
 static void *tsDnodeVnodesHash;
 static void  vnodeCleanUp(SVnodeObj *pVnode);
 static void  vnodeBuildVloadMsg(char *pNode, void * param);
+static int   vnodeWALCallback(void *arg);
 
 static int   tsOpennedVnodes;
 static pthread_once_t  vnodeModuleInit = PTHREAD_ONCE_INIT;
@@ -120,24 +121,29 @@ int32_t vnodeOpen(int32_t vnode, char *rootDir) {
   vnodeObj.version  = 0;  
   SVnodeObj *pVnode = (SVnodeObj *)taosAddIntHash(tsDnodeVnodesHash, vnodeObj.vgId, (char *)(&vnodeObj));
 
-  sprintf(temp, "%s/tsdb", rootDir);
-  void *pTsdb = tsdbOpenRepo(temp);
-  if (pTsdb == NULL) {
-    dError("pVnode:%p vgId:%d, failed to open tsdb at %s(%s)", pVnode, pVnode->vgId, temp, tstrerror(terrno));
-    taosDeleteIntHash(tsDnodeVnodesHash, pVnode->vgId);
-    return terrno;
-  }
-
   pVnode->wqueue = dnodeAllocateWqueue(pVnode);
   pVnode->rqueue = dnodeAllocateRqueue(pVnode);
 
   sprintf(temp, "%s/wal", rootDir);
   pVnode->wal      = walOpen(temp, 3, tsCommitLog);
-  pVnode->tsdb     = pTsdb;
   pVnode->sync     = NULL;
   pVnode->events   = NULL;
   pVnode->cq       = NULL;
 
+  STsdbAppH appH = {0};
+  appH.appH = (void *)pVnode;
+  appH.walCallBack = vnodeWALCallback;
+
+  sprintf(temp, "%s/tsdb", rootDir);
+  void *pTsdb = tsdbOpenRepo(temp, &appH);
+  if (pTsdb == NULL) {
+    dError("pVnode:%p vgId:%d, failed to open tsdb at %s(%s)", pVnode, pVnode->vgId, temp, tstrerror(terrno));
+    taosDeleteIntHash(tsDnodeVnodesHash, pVnode->vgId);
+    return terrno;
+  }
+
+  pVnode->tsdb = pTsdb;
+
   walRestore(pVnode->wal, pVnode, vnodeWriteToQueue);
 
   pVnode->status = VN_STATUS_READY;
@@ -249,3 +255,8 @@ static void vnodeCleanUp(SVnodeObj *pVnode) {
 
   vnodeRelease(pVnode);
 }
+
+static int vnodeWALCallback(void *arg) {
+  SVnodeObj *pVnode = arg;
+  return walRenew(pVnode->wal);
+}
\ No newline at end of file
diff --git a/src/vnode/tsdb/inc/tsdb.h b/src/vnode/tsdb/inc/tsdb.h
index 85575e1a8b0f77f2456e29acb207ba70d7afd1f5..b20711df1dc4b4a515dad83105bc9977588f5483 100644
--- a/src/vnode/tsdb/inc/tsdb.h
+++ b/src/vnode/tsdb/inc/tsdb.h
@@ -34,6 +34,15 @@ extern "C" {
 
 #define TSDB_INVALID_SUPER_TABLE_ID -1
 
+// --------- TSDB APPLICATION HANDLE DEFINITION
+typedef struct {
+  // WAL handle
+  void *appH;
+  int (*walCallBack)(void *);
+  int (*eventCallBack)(void *);
+  int (*cqueryCallBack)(void *);
+} STsdbAppH;
+
 // --------- TSDB REPOSITORY CONFIGURATION DEFINITION
 typedef struct {
   int8_t  precision;
@@ -55,7 +64,7 @@ typedef void tsdb_repo_t;  // use void to hide implementation details from outsi
 
 int            tsdbCreateRepo(char *rootDir, STsdbCfg *pCfg, void *limiter);
 int32_t        tsdbDropRepo(tsdb_repo_t *repo);
-tsdb_repo_t *  tsdbOpenRepo(char *tsdbDir);
+tsdb_repo_t *  tsdbOpenRepo(char *tsdbDir, STsdbAppH *pAppH);
 int32_t        tsdbCloseRepo(tsdb_repo_t *repo);
 int32_t        tsdbConfigRepo(tsdb_repo_t *repo, STsdbCfg *pCfg);
 int32_t        tsdbTriggerCommit(tsdb_repo_t *repo);
diff --git a/src/vnode/tsdb/inc/tsdbMain.h b/src/vnode/tsdb/inc/tsdbMain.h
index a9021550451c387aa85643b17bec81f02fa03ae3..06f62ea6f728620f01b70a16794b566d6eae273b 100644
--- a/src/vnode/tsdb/inc/tsdbMain.h
+++ b/src/vnode/tsdb/inc/tsdbMain.h
@@ -322,6 +322,8 @@ typedef struct _tsdb_repo {
   // TSDB configuration
   STsdbCfg config;
 
+  STsdbAppH appH;
+
   // The meter meta handle of this TSDB repository
   STsdbMeta *tsdbMeta;
 
diff --git a/src/vnode/tsdb/src/tsdbMain.c b/src/vnode/tsdb/src/tsdbMain.c
index cb59c004efed1533326a8517e657f177aef16c29..1a8e50d0eeab0ded741d19ae71b796d9f19343fd 100644
--- a/src/vnode/tsdb/src/tsdbMain.c
+++ b/src/vnode/tsdb/src/tsdbMain.c
@@ -177,7 +177,7 @@ int32_t tsdbDropRepo(tsdb_repo_t *repo) {
  *
  * @return a TSDB repository handle on success, NULL for failure and the error number is set
  */
-tsdb_repo_t *tsdbOpenRepo(char *tsdbDir) {
+tsdb_repo_t *tsdbOpenRepo(char *tsdbDir, STsdbAppH *pAppH) {
   char dataDir[128] = "\0";
   if (access(tsdbDir, F_OK | W_OK | R_OK) < 0) {
     return NULL;
@@ -191,6 +191,7 @@ tsdb_repo_t *tsdbOpenRepo(char *tsdbDir) {
   pRepo->rootDir = strdup(tsdbDir);
 
   tsdbRestoreCfg(pRepo, &(pRepo->config));
+  if (pAppH) pRepo->appH = *pAppH;
 
   pRepo->tsdbMeta = tsdbInitMeta(tsdbDir, pRepo->config.maxTables);
   if (pRepo->tsdbMeta == NULL) {
diff --git a/src/vnode/tsdb/tests/tsdbTests.cpp b/src/vnode/tsdb/tests/tsdbTests.cpp
index d3a5b680aad5999d573442278f1a8928fad29ed9..9ee49d6a708a65b3344fc5fd56f458b0a9dd23cc 100644
--- a/src/vnode/tsdb/tests/tsdbTests.cpp
+++ b/src/vnode/tsdb/tests/tsdbTests.cpp
@@ -140,7 +140,7 @@ TEST(TsdbTest, createRepo) {
 
 // TEST(TsdbTest, DISABLED_openRepo) {
 TEST(TsdbTest, openRepo) {
-  tsdb_repo_t *repo = tsdbOpenRepo("/home/ubuntu/work/ttest/vnode0");
+  tsdb_repo_t *repo = tsdbOpenRepo("/home/ubuntu/work/ttest/vnode0", NULL);
   ASSERT_NE(repo, nullptr);
 
   STsdbRepo *pRepo = (STsdbRepo *)repo;