diff --git a/src/tsdb/inc/tsdbFS.h b/src/tsdb/inc/tsdbFS.h
index 281ee7dc682858a1f84e3affc3fb6457b090dc78..9b7ad04b7cc06fb6e8b2a6b8ba866df6103ce44f 100644
--- a/src/tsdb/inc/tsdbFS.h
+++ b/src/tsdb/inc/tsdbFS.h
@@ -25,7 +25,7 @@ extern "C" {
 // ================== CURRENT file header info
 typedef struct {
   uint32_t version;  // Current file version
-  uint32_t len;
+  uint32_t len;      // Encode content length (including checksum)
 } SFSHeader;
 
 // ================== TSDB File System Meta
@@ -38,6 +38,7 @@ typedef struct {
 // ==================
 typedef struct {
   STsdbFSMeta meta;  // FS meta
+  SMFile*     pmf;   // meta file pointer
   SMFile      mf;    // meta file
   SArray*     df;    // data file array
 } SFSStatus;
@@ -45,12 +46,10 @@ typedef struct {
 typedef struct {
   pthread_rwlock_t lock;
 
-  SFSStatus* cstatus;    // current stage
-  SHashObj*  metaCache;  // meta
-
+  SFSStatus* cstatus;    // current status
+  SHashObj*  metaCache;  // meta cache
   bool       intxn;
-  SFSStatus* nstatus;
-  SList*     metaDelta;
+  SFSStatus* nstatus;  // new status
 } STsdbFS;
 
 #define FS_CURRENT_STATUS(pfs) ((pfs)->cstatus)
@@ -58,12 +57,17 @@ typedef struct {
 #define FS_IN_TXN(pfs) (pfs)->intxn
 
 typedef struct {
+  int        direction;
   uint64_t   version;  // current FS version
-  int        index;
-  int        fid;
+  STsdbFS*   pfs;
+  int        index;  // used to position next fset when version the same
+  int        fid;    // used to seek when version is changed
   SDFileSet* pSet;
 } SFSIter;
 
+#define TSDB_FS_ITER_FORWARD TSDB_ORDER_ASC
+#define TSDB_FS_ITER_BACKWARD TSDB_ORDER_DESC
+
 #if 0
 int        tsdbOpenFS(STsdbRepo* pRepo);
 void       tsdbCloseFS(STsdbRepo* pRepo);
diff --git a/src/tsdb/inc/tsdbFile.h b/src/tsdb/inc/tsdbFile.h
index 7e62f6acef7afc1cfc3408609c1a118c4c4f7803..182fc9d443da8dacfe30d1094ed2ab867b073713 100644
--- a/src/tsdb/inc/tsdbFile.h
+++ b/src/tsdb/inc/tsdbFile.h
@@ -23,12 +23,14 @@ extern "C" {
 #define TSDB_FILE_HEAD_SIZE 512
 #define TSDB_FILE_DELIMITER 0xF00AFA0F
 #define TSDB_FILE_INIT_MAGIC 0xFFFFFFFF
+#define TSDB_IVLD_FID INT_MIN
 
 #define TSDB_FILE_INFO(tf) (&((tf)->info))
 #define TSDB_FILE_F(tf) (&((tf)->f))
 #define TSDB_FILE_FD(tf) ((tf)->fd)
 #define TSDB_FILE_FULL_NAME(tf) TFILE_NAME(TSDB_FILE_F(tf))
 #define TSDB_FILE_OPENED(tf) (TSDB_FILE_FD(tf) >= 0)
+#define TSDB_FILE_CLOSED(tf) (!TSDB_FILE_OPENED(tf))
 #define TSDB_FILE_SET_CLOSED(f) (TSDB_FILE_FD(f) = -1)
 #define TSDB_FILE_LEVEL(tf) TFILE_LEVEL(TSDB_FILE_F(tf))
 #define TSDB_FILE_ID(tf) TFILE_ID(TSDB_FILE_F(tf))
@@ -61,6 +63,7 @@ void  tsdbInitMFile(SMFile* pMFile, SDiskID did, int vid, int ver);
 void  tsdbInitMFileEx(SMFile* pMFile, SMFile* pOMFile);
 int   tsdbEncodeSMFile(void** buf, SMFile* pMFile);
 void* tsdbDecodeSMFile(void* buf, SMFile* pMFile);
+int   tsdbApplyMFileChange(const SMFile* from, const SMFile* to);
 
 static FORCE_INLINE int tsdbOpenMFile(SMFile* pMFile, int flags) {
   ASSERT(!TSDB_FILE_OPENED(pMFile));
@@ -288,6 +291,7 @@ void  tsdbInitDFileSet(SDFileSet* pSet, SDiskID did, int vid, int fid, int ver);
 void  tsdbInitDFileSetEx(SDFileSet* pSet, SDFileSet* pOSet);
 int   tsdbEncodeDFileSet(void** buf, SDFileSet* pSet);
 void* tsdbDecodeDFileSet(void* buf, SDFileSet* pSet);
+int   tsdbApplyDFileSetChange(const SDFileSet* from, const SDFileSet* to);
 
 static FORCE_INLINE void tsdbCloseDFileSet(SDFileSet* pSet) {
   for (TSDB_FILE_T ftype = 0; ftype < TSDB_FILE_MAX; ftype++) {
diff --git a/src/tsdb/src/tsdbCommit.c b/src/tsdb/src/tsdbCommit.c
index 5dd3dc70bcc567e420568b3b21f3e3fdb48ae185..7901c4fb8e2067fe16b03ef77f59f38397326107 100644
--- a/src/tsdb/src/tsdbCommit.c
+++ b/src/tsdb/src/tsdbCommit.c
@@ -14,7 +14,6 @@
  */
 #include "tsdbint.h"
 
-#define TSDB_IVLD_FID INT_MIN
 #define TSDB_MAX_SUBBLOCKS 8
 #define TSDB_KEY_FID(key, days, precision) ((key) / tsMsPerDay[(precision)] / (days))
 
diff --git a/src/tsdb/src/tsdbFS.c b/src/tsdb/src/tsdbFS.c
index 7bdbe35c38517075eba2009f9837002e94cdd7b9..1e748c0286b2093a61cc2fdc504c3027a491e25b 100644
--- a/src/tsdb/src/tsdbFS.c
+++ b/src/tsdb/src/tsdbFS.c
@@ -15,6 +15,8 @@
 
 #include "tsdbint.h"
 
+#define TSDB_FS_CURRENT_FNAME "current"
+#define TSDB_FS_TEMP_FNAME "current.t"
 #define TSDB_MAX_FSETS(keep, days) ((keep) / (days) + 3)
 
 // ================== CURRENT file header info
@@ -27,9 +29,9 @@ static int tsdbEncodeFSHeader(void **buf, SFSHeader *pHeader) {
   return tlen;
 }
 
-static void *tsdbEncodeFSHeader(void *buf, SFSHeader *pHeader) {
-  buf = taosEncodeFixedU32(buf, &(pHeader->version));
-  buf = taosEncodeFixedU32(buf, &(pHeader->len));
+static void *tsdbDecodeFSHeader(void *buf, SFSHeader *pHeader) {
+  buf = taosDecodeFixedU32(buf, &(pHeader->version));
+  buf = taosDecodeFixedU32(buf, &(pHeader->len));
 
   return buf;
 }
@@ -76,8 +78,6 @@ static int tsdbDecodeDFileSetArray(void *buf, SArray *pArray) {
 
   buf = taosDecodeFixedU64(buf, &nset);
   for (size_t i = 0; i < nset; i++) {
-    SDFileSet *pSet = taosArrayGet(pArray, i);
-
     buf = tsdbDecodeDFileSet(buf, &dset);
     taosArrayPush(pArray, (void *)(&dset));
   }
@@ -85,19 +85,22 @@ static int tsdbDecodeDFileSetArray(void *buf, SArray *pArray) {
 }
 
 static int tsdbEncodeFSStatus(void **buf, SFSStatus *pStatus) {
+  ASSERT(pStatus->pmf);
+
   int tlen = 0;
 
-  tlen += tsdbEncodeFSMeta(buf, &(pStatus->meta));
-  tlen += tsdbEncodeSMFile(buf, &(pStatus->mf));
+  tlen += tsdbEncodeSMFile(buf, &(pStatus->pmf));
   tlen += tsdbEncodeDFileSetArray(buf, pStatus->df);
 
   return tlen;
 }
 
 static void *tsdbDecodeFSStatus(void *buf, SFSStatus *pStatus) {
-  buf = taosDecodeFixedU32(buf, pStatus->fsVer);
-  buf = tsdbDecodeFSMeta(buf, &(pStatus->meta));
-  buf = tsdbDecodeSMFile(buf, &(pStatus->mf));
+  tsdbResetFSStatus(pStatus);
+
+  pStatus->pmf = &(pStatus->mf);
+
+  buf = tsdbDecodeSMFile(buf, pStatus->pmf);
   buf = tsdbDecodeDFileSetArray(buf, pStatus->df);
 
   return buf;
@@ -111,7 +114,7 @@ static SFSStatus *tsdbNewFSStatus(int maxFSet) {
   }
 
   pStatus->df = taosArrayInit(maxFSet, sizeof(SDFileSet));
-  if (pStatus->df) {
+  if (pStatus->df == NULL) {
     terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
     free(pStatus);
     return NULL;
@@ -134,62 +137,79 @@ static void tsdbResetFSStatus(SFSStatus *pStatus) {
     return;
   }
 
+  pStatus->pmf = NULL;
   taosArrayClear(pStatus->df);
 }
 
+static void tsdbSetStatusMFile(SFSStatus *pStatus, const SMFile *pMFile) {
+  ASSERT(pStatus->pmf == NULL && TSDB_FILE_CLOSED(pMFile));
+
+  pStatus->pmf = &(pStatus->mf);
+  *(pStatus->pmf) = *pMFile;
+}
+
+static int tsdbAddDFileSetToStatus(SFSStatus *pStatus, const SDFileSet *pSet) {
+  ASSERT(TSDB_FILE_CLOSED(&(pSet->files[0])));
+  ASSERT(TSDB_FILE_CLOSED(&(pSet->files[1])));
+  ASSERT(TSDB_FILE_CLOSED(&(pSet->files[2])));
+
+  if (taosArrayPush(pStatus->df, (void *)pStatus) == NULL) {
+    terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
+    return -1;
+  }
+
+  return 0;
+}
+
 // ================== STsdbFS
-STsdbFS *tsdbNewFS(int maxFSet) {
-  STsdbFS *pFs = (STsdbFS *)calloc(1, sizeof(*pFs));
-  if (pFs == NULL) {
+STsdbFS *tsdbNewFS(int keep, int days) {
+  int      maxFSet = TSDB_MAX_FSETS(keep, days);
+  STsdbFS *pfs;
+
+  pfs = (STsdbFS *)calloc(1, sizeof(*pfs));
+  if (pfs == NULL) {
     terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
     return NULL;
   }
 
-  int code = pthread_rwlock_init(&(pFs->lock), NULL);
+  int code = pthread_rwlock_init(&(pfs->lock), NULL);
   if (code) {
     terrno = TAOS_SYSTEM_ERROR(code);
-    free(pFs);
+    free(pfs);
     return NULL;
   }
 
-  pFs->cstatus = tsdbNewFSStatus(maxFSet);
-  if (pFs->cstatus == NULL) {
-    tsdbFreeFS(pFs);
+  pfs->cstatus = tsdbNewFSStatus(maxFSet);
+  if (pfs->cstatus == NULL) {
+    tsdbFreeFS(pfs);
     return NULL;
   }
 
-  pFs->metaCache = taosHashInit(4096, taosGetDefaultHashFunction(TSDB_DATA_TYPE_BIGINT), true, false);
-  if (pFs->metaCache == NULL) {
+  pfs->metaCache = taosHashInit(4096, taosGetDefaultHashFunction(TSDB_DATA_TYPE_BIGINT), true, HASH_NO_LOCK);
+  if (pfs->metaCache == NULL) {
     terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
-    tsdbFreeFS(pFs);
+    tsdbFreeFS(pfs);
     return NULL;
   }
 
-  pFs->nstatus = tsdbNewFSStatus(maxFSet);
-  if (pFs->nstatus == NULL) {
-    tsdbFreeFS(pFs);
+  pfs->nstatus = tsdbNewFSStatus(maxFSet);
+  if (pfs->nstatus == NULL) {
+    tsdbFreeFS(pfs);
     return NULL;
   }
 
-  pFs->metaDelta = tdListNew(sizeof(SKVRecord));
-  if (pFs->metaDelta == NULL) {
-    terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
-    tsdbFreeFS(pFs);
-    return NULL;
-  }
-
-  return NULL;
+  return pfs;
 }
 
-void *tsdbFreeFS(STsdbFS *pFs) {
-  if (pFs) {
-    pFs->metaDelta = tdListFree(pFs->metaDelta);
-    pFs->nstatus = tsdbFreeFSStatus(pFs->nstatus);
-    taosHashCleanup(pFs->metaCache);
-    pFs->metaCache = NULL;
-    pFs->cstatus = tsdbFreeFSStatus(pFs->cstatus);
-    pthread_rwlock_destroy(&(pFs->lock));
+void *tsdbFreeFS(STsdbFS *pfs) {
+  if (pfs) {
+    pfs->nstatus = tsdbFreeFSStatus(pfs->nstatus);
+    taosHashCleanup(pfs->metaCache);
+    pfs->metaCache = NULL;
+    pfs->cstatus = tsdbFreeFSStatus(pfs->cstatus);
+    pthread_rwlock_destroy(&(pfs->lock));
   }
+
   return NULL;
 }
 
@@ -203,428 +223,271 @@ void tsdbCloseFS(STsdbFS *pFs) {
   // TODO
 }
 
-int tsdbStartTxn(STsdbFS *pFs) {
-  tsdbResetFSStatus(pFs->nstatus);
-  tdListEmpty(pFs->metaDelta);
-  return 0;
-}
+// Start a new transaction to modify the file system
+int tsdbStartTxn(STsdbFS *pfs) {
+  ASSERT(pfs->intxn == false);
 
-int tsdbEndTxn(STsdbFS *pFs, bool hasError) {
-  SFSStatus *pTStatus;
+  pfs->intxn = true;
+  tsdbResetFSStatus(pfs->nstatus);
 
-  if (hasError) {
-    // TODO
-  } else {
-    // TODO 1. Create and open a new file current.t
+  return 0;
+}
 
-    // TODO 2. write new status to new file and fysnc and close
+int tsdbEndTxn(STsdbFS *pfs) {
+  ASSERT(FS_IN_TXN(pfs));
+  SFSStatus *pStatus;
 
-    // TODO 3. rename current.t to current
+  // Write current file system snapshot
+  if (tsdbUpdateFS(pfs) < 0) {
+    tsdbEndTxnWithError(pfs);
+    return -1;
+  }
 
-    // TODO 4. apply change to file
-    tsdbWLockFS(pFs);
-    pTStatus = pFs->cstatus;
-    pFs->cstatus = pFs->nstatus;
-    pFs->nstatus = pTStatus;
-    tsdbUnLockFS(pFs);
+  // Make new 
+  tsdbWLockFS(pfs);
+  pStatus = pfs->cstatus;
+  pfs->cstatus = pfs->nstatus;
+  pfs->nstatus = pStatus;
+  tsdbUnLockFS(pfs);
 
-    // TODO 5: apply meta change to cache
-  }
+  // Apply actual change to each file and SDFileSet
+  tsdbApplyFSChangeOnDisk(pfs);
 
+  pfs->intxn = false;
   return 0;
 }
 
-// ================== SFSIter
-void tsdbFSIterInit(STsdbFS *pFs, SFSIter *pIter) {
+int tsdbEndTxnWithError(STsdbFS *pfs) {
   // TODO
+  pfs->intxn = false;
+  return 0;
 }
 
-SDFileSet *tsdbFSIterNext(STsdbFS *pFs) {
-  // TODO
-  return NULL;
-}
+void tsdbUpdateMFile(STsdbFS *pfs, const SMFile *pMFile) { tsdbSetStatusMFile(pfs->nstatus, pMFile); }
 
-#if 0
-int tsdbOpenFS(STsdbRepo *pRepo) {
-  ASSERT(REPO_FS == NULL);
+int tsdbUpdateDFileSet(STsdbFS *pfs, const SDFileSet *pSet) { return tsdbAddDFileSetToStatus(pfs->nstatus, pSet); }
 
-  STsdbCfg *pCfg = TSDB_CFG(pRepo);
+static int tsdbUpdateFS(STsdbFS *pfs) {
+  ASSERT(FS_IN_TXN(pfs));
+  SFSHeader fsheader;
+  void *    pBuf = NULL;
+  void *    ptr;
+  char      hbuf[TSDB_FILE_HEAD_SIZE] = "\0";
 
-  // Create fs object
-  REPO_FS(pRepo) = tsdbNewFS(pCfg->keep, pCfg->daysPerFile);
-  if (REPO_FS(pRepo) == NULL) {
-    tsdbError("vgId:%d failed to open TSDB FS since %s", REPO_ID(pRepo), tstrerror(terrno));
+  int fd = open(TSDB_FS_TEMP_FNAME, O_WRONLY | O_CREAT | O_TRUNC, 0755);
+  if (fd < 0) {
+    terrno = TAOS_SYSTEM_ERROR(errno);
     return -1;
   }
 
-  // Load TSDB file system from disk
-  if (tsdbOpenFSImpl(pRepo) < 0) {
-    tsdbError("vgId:%d failed to open TSDB FS since %s", REPO_ID(pRepo), tstrerror(terrno));
-    tsdbCloseFS(pRepo);
-    return -1;
+  fsheader.version = TSDB_FS_VERSION;
+  if (pfs->nstatus->pmf == NULL) {
+    ASSERT(taosArrayGetSize(pfs->nstatus->df) == 0);
+    fsheader.len = 0;
+  } else {
+    fsheader.len = tsdbEncodeFSHeader(NULL, pfs->nstatus) + sizeof(TSCKSUM);
   }
 
-  return 0;
-}
+  // Encode header part and write
+  ptr = hbuf;
+  tsdbEncodeFSHeader(&ptr, &fsheader);
+  tsdbEncodeFSMeta(&ptr, &(pfs->nstatus->meta));
 
-void tsdbCloseFS(STsdbRepo *pRepo) {
-  REPO_FS(pRepo) = tsdbFreeFS(REPO_FS(pRepo));
-  return 0;
-}
-
-// Start a new FS transaction
-int tsdbFSNewTxn(STsdbRepo *pRepo) {
-  STsdbFS *pFs = REPO_FS(pRepo);
+  taosCalcChecksumAppend(0, (uint8_t *)hbuf, TSDB_FILE_HEAD_SIZE);
 
-  if (tsdbCopySnapshot(pFs->curr, pFs->new) < 0) {
+  if (taosWrite(fd, hbuf, TSDB_FILE_HEAD_SIZE) < TSDB_FILE_HEAD_SIZE) {
+    terrno = TAOS_SYSTEM_ERROR(errno);
+    close(fd);
+    remove(TSDB_FS_TEMP_FNAME);
     return -1;
   }
 
-  pFs->new->version++;
-
-  return 0;
-}
-
-// End an existing FS transaction
-int tsdbFSEndTxn(STsdbRepo *pRepo, bool hasError) {
-  STsdbFS *pFs = REPO_FS(pRepo);
-
-  if (hasError) { // roll back files
-
-  } else { // apply file change
-    if (tsdbSaveFSSnapshot(-1, pFs->new) < 0) {
-      // TODO
+  // Encode file status and write to file
+  if (fsheader.len > 0) {
+    if (tsdbMakeRoom(&(pBuf), fsheader.len) < 0) {
+      close(fd);
+      remove(TSDB_FS_TEMP_FNAME);
+      return -1;
     }
 
-    // rename();
-
-    // apply all file changes
-
-  }
-
-  return 0;
-}
+    ptr = pBuf;
+    tsdbEncodeFSStatus(&ptr, pfs->nstatus);
+    taosCalcChecksumAppend(0, (uint8_t *)pBuf, fsheader.len) 
 
-int tsdbUpdateMFile(STsdbRepo *pRepo, SMFile *pMFile) {
-  STsdbFS *pFs = REPO_FS(pRepo);
-  pFs->new->mf = *pMFile;
-  return 0;
-}
-
-int tsdbUpdateDFileSet(STsdbRepo *pRepo, SDFileSet *pSet) {
-  SFSStatus *pSnapshot = REPO_FS(pRepo)->new;
-  SDFileSet *  pOldSet;
-
-  pOldSet = tsdbSearchDFileSet(pSnapshot, pSet->id, TD_GE);
-  if (pOldSet == NULL) {
-    if (taosArrayPush(pSnapshot->df, pSet) == NULL) {
-      terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
+    if (taosWrite(fd, pBuf, fsheader.len) < fsheader.len) {
+      terrno = TAOS_SYSTEM_ERROR(errno);
+      close(fd);
+      remove(TSDB_FS_TEMP_FNAME);
+      taosTZfree(pBuf);
       return -1;
     }
-  } else {
-    int index = TARRAY_ELEM_IDX(pSnapshot->df, pOldSet);
-
-    if (pOldSet->id == pSet->id) {
-      taosArraySet(pSnapshot->df, index, pSet);
-    } else if (pOldSet->id > pSet->id) {
-      if (taosArrayInsert(pSnapshot->df, index, pSet) == NULL) {
-        terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
-        return -1;
-      }
-    } else {
-      ASSERT(0);
-    }
   }
 
-  return 0;
-}
-
-void tsdbRemoveExpiredDFileSet(STsdbRepo *pRepo, int mfid) {
-  SFSStatus *pSnapshot = REPO_FS(pRepo)->new;
-  while (taosArrayGetSize(pSnapshot->df) > 0) {
-    SDFileSet *pSet = (SDFileSet *)taosArrayGet(pSnapshot->df, 0);
-    if (pSet->id < mfid) {
-      taosArrayRemove(pSnapshot->df, 0);
-    }
+  // fsync, close and rename
+  if (fsync(fd) < 0) {
+    terrno = TAOS_SYSTEM_ERROR(errno);
+    close(fd);
+    remove(TSDB_FS_TEMP_FNAME);
+    taosTZfree(pBuf);
+    return -1;
   }
-}
-
 
-SDFileSet tsdbMoveDFileSet(SDFileSet *pOldSet, int to) {
-  // TODO
-}
+  (void)close(fd);
+  (void)rename(TSDB_FS_TEMP_FNAME, TSDB_FS_CURRENT_FNAME);
+  taosTZfree(pBuf);
 
-int tsdbInitFSIter(STsdbRepo *pRepo, SFSIter *pIter) {
-  // TODO
   return 0;
 }
 
-SDFileSet *tsdbFSIterNext(SFSIter *pIter) {
-  // TODO
-  return NULL;
-}
+static void tsdbApplyFSChangeOnDisk(SFSStatus *pFrom, SFSStatus *pTo) {
+  int        ifrom = 0;
+  int        ito = 0;
+  size_t     sizeFrom, sizeTo;
+  SDFileSet *pSetFrom;
+  SDFileSet *pSetTo;
 
-static int tsdbSaveFSSnapshot(int fd, SFSStatus *pSnapshot) {
-  // TODO
-  return 0;
-}
+  sizeFrom = taosArrayGetSize(pFrom->df);
+  sizeTo = taosArrayGetSize(pTo->df);
 
-static int tsdbLoadFSSnapshot(SFSStatus *pSnapshot) {
-  // TODO
-  return 0;
-}
+  // Apply meta file change
+  tsdbApplyMFileChange(pFrom->pmf, pTo->pmf);
 
-static int tsdbOpenFSImpl(STsdbRepo *pRepo) {
-  char manifest[TSDB_FILENAME_LEN] = "\0";
-
-  // TODO: use API here
-  sprintf(manifest, "%s/manifest", pRepo->rootDir);
-
-  if (access(manifest, F_OK) == 0) {
-    // manifest file exist, just load
-    // TODO
+  // Apply SDFileSet change
+  if (ifrom >= sizeFrom) {
+    pSetFrom = NULL;
   } else {
-    // manifest file not exists, scan all the files and construct 
-    // TODO
+    pSetFrom = taosArrayGet(pFrom->df, ifrom);
   }
 
-  return 0;
-}
-
+  if (ito >= sizeTo) {
+    pSetTo = NULL;
+  } else {
+    pSetTo = taosArrayGet(pTo->df, ito);
+  }
 
-static int tsdbEncodeFSMeta(void **buf, STsdbFSMeta *pMeta) {
-  int tlen = 0;
+  while (true) {
+    if ((pSetTo == NULL) && (pSetFrom == NULL)) break;
 
-  tlen += taosEncodeVariantI64(buf, pMeta->fsversion);
-  tlen += taosEncodeVariantI64(buf, pMeta->version);
-  tlen += taosEncodeVariantI64(buf, pMeta->totalPoints);
-  tlen += taosEncodeVariantI64(buf, pMeta->totalStorage);
+    if (pSetTo == NULL || (pSetFrom && pSetFrom->fid < pSetTo->fid)) {
+      tsdbApplyDFileSetChange(pSetFrom, NULL);
 
-  return tlen;
-}
+      ifrom++;
+      if (ifrom >= sizeFrom) {
+        pSetFrom = NULL;
+      } else {
+        pSetFrom = taosArrayGet(pFrom->df, ifrom);
+      }
+    } else if (pSetFrom == NULL || pSetFrom->fid > pSetTo->fid) {
+      // Do nothing
+      if (pSetFrom) {
+        ito++;
+        if (ito >= sizeTo) {
+          pSetTo = NULL;
+        } else {
+          pSetTo = taosArrayGet(pTo->df, ito);
+        }
+      }
+    } else {
+      tsdbApplyDFileSetChange(pSetFrom, pSetTo);
 
-static void *tsdbDecodeFSMeta(void *buf, STsdbFSMeta *pMeta) {
-  buf = taosDecodeVariantI64(buf, &(pMeta->fsversion));
-  buf = taosDecodeVariantI64(buf, &(pMeta->version));
-  buf = taosDecodeVariantI64(buf, &(pMeta->totalPoints));
-  buf = taosDecodeVariantI64(buf, &(pMeta->totalStorage));
+      ifrom++;
+      if (ifrom >= sizeFrom) {
+        pSetFrom = NULL;
+      } else {
+        pSetFrom = taosArrayGet(pFrom->df, ifrom);
+      }
 
-  return buf;
+      ito++;
+      if (ito >= sizeTo) {
+        pSetTo = NULL;
+      } else {
+        pSetTo = taosArrayGet(pTo->df, ito);
+      }
+    }
+  }
 }
 
-static int tsdbEncodeFSSnapshot(void **buf, SFSStatus *pSnapshot) {
-  int     tlen = 0;
-  int64_t size = 0;
-
-  // Encode meta file
-  tlen += tsdbEncodeMFile(buf, &(pSnapshot->mf));
-
-  // Encode data files
-  size = taosArrayGetSize(pSnapshot->df);
-  tlen += taosEncodeVariantI64(buf, size);
-  for (size_t index = 0; index < size; index++) {
-    SDFile *pFile = taosArrayGet(pSnapshot->df, index);
-    
-    tlen += tsdbEncodeDFInfo(buf, &pFile);
-  }
-  
+// ================== SFSIter
+// ASSUMPTIONS: the FS Should be read locked when calling these functions
+void tsdbFSIterInit(SFSIter *pIter, STsdbFS *pfs, int direction) {
+  pIter->pfs = pfs;
+  pIter->direction = direction;
 
-  return tlen;
-}
+  size_t size = taosArrayGetSize(pfs->cstatus->df);
 
-static void *tsdbDecodeFSSnapshot(void *buf, SFSStatus *pSnapshot) {
-  int64_t size = 0;
-  SDFile  df;
+  pIter->version = pfs->cstatus->meta.version;
 
-  // Decode meta file
-  buf = tsdbDecodeMFile(buf, &(pSnapshot->mf));
+  if (size == 0) {
+    pIter->index = -1;
+    pIter->fid = TSDB_IVLD_FID;
+  } else {
+    if (direction == TSDB_FS_ITER_FORWARD) {
+      pIter->index = 0;
+    } else {
+      pIter->index = size - 1;
+    }
 
-  // Decode data files
-  buf = taosDecodeVariantI64(buf, &size);
-  for (size_t index = 0; index < size; index++) {
-    buf = tsdbDecodeDFInfo(buf, &df);
-    taosArrayPush(pSnapshot->df, (void *)(&df));
+    pIter->fid = ((SDFileSet *)taosArrayGet(pfs->cstatus->df, pIter->index))->fid;
   }
-
-  return buf;
 }
 
-static SFSStatus *tsdbNewSnapshot(int32_t nfiles) {
-  SFSStatus *pSnapshot;
-
-  pSnapshot = (SFSStatus *)calloc(1, sizeof(pSnapshot));
-  if (pSnapshot == NULL) {
-    terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
-    return NULL;
-  }
+void tsdbFSIterSeek(SFSIter *pIter, int fid) {
+  STsdbFS *pfs = pIter->pfs;
+  size_t   size = taosArrayGetSize(pfs->cstatus->df);
 
-  pSnapshot->df = taosArrayInit(nfiles, sizeof(SDFileSet));
-  if (pSnapshot->df == NULL) {
-    terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
-    free(pSnapshot);
-    return NULL;
+  int flags;
+  if (pIter->direction == TSDB_FS_ITER_FORWARD) {
+    flags = TD_GE;
+  } else {
+    flags = TD_LE;
   }
 
-  return pSnapshot;
-}
-
-static SFSStatus *tsdbFreeSnapshot(SFSStatus *pSnapshot) {
-  if (pSnapshot) {
-    taosArrayDestroy(pSnapshot->df);
-    free(pSnapshot);
+  void *ptr = taosbsearch(&fid, pfs->cstatus->df->pData, size, sizeof(SDFileSet), , flags);
+  if (ptr == NULL) {
+    pIter->index = -1;
+    pIter->fid = TSDB_IVLD_FID;
+  } else {
+    pIter->index = TARRAY_ELEM_IDX(pfs->cstatus->df, ptr);
+    pIter->fid = ((SDFileSet *)ptr)->fid;
   }
-
-  return NULL;
 }
 
-static STsdbFS *tsdbNewFS(int32_t keep, int32_t days) {
-  STsdbFS *pFs;
-  int      code;
-  int32_t  nfiles;
-
-  pFs = (STsdbFS *)calloc(1, sizeof(*pFs));
-  if (pFs == NULL) {
-    terrno = TSDB_CODE_TDB_OUT_OF_MEMORY;
-    return NULL;
-  }
-
-  code = pthread_rwlock_init(&(pFs->lock));
-  if (code != 0) {
-    terrno = TAOS_SYSTEM_ERROR(code);
-    free(pFs);
-    return NULL;
-  }
+SDFileSet *tsdbFSIterNext(SFSIter *pIter) {
+  STsdbFS *  pfs = pIter->pfs;
+  SDFileSet *pSet;
 
-  nfiles = TSDB_MAX_DFILES(keep, days);
-  if (((pFs->curr = tsdbNewSnapshot(nfiles)) == NULL) || ((pFs->new = tsdbNewSnapshot(nfiles)) == NULL)) {
-    tsdbFreeFS(pFs);
+  if (pIter->index < 0) {
+    ASSERT(pIter->fid == TSDB_IVLD_FID);
     return NULL;
   }
 
-  return pFs;
-}
+  ASSERT(pIter->fid != TSDB_IVLD_FID);
 
-static STsdbFS *tsdbFreeFS(STsdbFS *pFs) {
-  if (pFs) {
-    pFs->new = tsdbFreeSnapshot(pFs->new);
-    pFs->curr = tsdbFreeSnapshot(pFs->curr);
-    pthread_rwlock_destroy(&(pFs->lock));
-    free(pFs);
+  if (pIter->version != pfs->cstatus->meta.version) {
+    tsdbFSIterSeek(pIter, pIter->fid);
   }
 
-  return NULL;
-}
-
-static int tsdbCopySnapshot(SFSStatus *src, SFSStatus *dst) {
-  dst->meta = src->meta;
-  dst->mf = src->meta;
-  taosArrayCopy(dst->df, src->df);
-  return 0;
-}
-
-static int tsdbCompFSetId(const void *key1, const void *key2) {
-  int        id = *(int *)key1;
-  SDFileSet *pSet = (SDFileSet *)key2;
-
-  if (id < pSet->id) {
-    return -1;
-  } else if (id == pSet->id) {
-    return 0;
-  } else {
-    return 1;
+  if (pIter->index < 0) {
+    return NULL;
   }
-}
-
-static SDFileSet *tsdbSearchDFileSet(SFSStatus *pSnapshot, int fid, int flags) {
-  void *ptr = taosArraySearch(pSnapshot->df, (void *)(&fid), tsdbCompFSetId, flags);
-  return (ptr == NULL) ? NULL : ((SDFileSet *)ptr);
-}
 
-static int tsdbMakeFSChange(STsdbRepo *pRepo) {
-  tsdbMakeFSMFileChange(pRepo);
-  tsdbMakeFSDFileChange(pRepo);
-  return 0;
-}
+  pSet = (SDFileSet *)taosArrayGet(pfs->cstatus->df, pIter->index);
+  ASSERT(pSet->fid == pIter->fid);
 
-static int tsdbMakeFSMFileChange(STsdbRepo *pRepo) {
-  STsdbFS *pFs = REPO_FS(pRepo);
-  SMFile * pDstMFile = &(pFs->curr->mf);
-  SMFile * pSrcMFile = &(pFs->new->mf);
-
-  if (tfsIsSameFile(&(pDstMFile->f), &(pSrcMFile->f))) { // the same file
-    if (pDstMFile->info != pSrcMFile->info) {
-      if (pDstMFile->info.size > pDstMFile->info.size) {
-        // Commit succeed, do nothing
-      } else if (pDstMFile->info.size < pDstMFile->info.size) {
-        // Commit failed, back
-        // TODO
-      } else {
-        ASSERT(0);
-      }
+  if (pIter->direction == TSDB_FS_ITER_FORWARD) {
+    pIter->index++;
+    if (pIter->index >= taosArrayGetSize(pfs->cstatus->df)) {
+      pIter->index = -1;
     }
   } else {
-    tfsremove(&(pSrcMFile->f));
+    pIter->index--;
   }
 
-  return 0;
-}
-
-static int tsdbMakeFSDFileChange(STsdbRepo *pRepo) {
-  STsdbFS *  pFs = REPO_FS(pRepo);
-  int        cidx = 0;
-  int        nidx = 0;
-  SDFileSet *pCSet = NULL;
-  SDFileSet *pNSet = NULL;
-
-  if (cidx < taosArrayGetSize(pFs->curr->df)) {
-    pCSet = taosArrayGet(pFs->curr->df, cidx);
-  } else {
-    pCSet = NULL;
-  }
-
-  if (nidx < taosArrayGetSize(pFs->new->df)) {
-    pNSet = taosArrayGet(pFs->new->df, nidx);
+  if (pIter->index > 0) {
+    pIter->fid = ((SDFileSet *)taosArrayGet(pfs->cstatus->df, pIter->index))->fid;
   } else {
-    pNSet = NULL;
-  }
-
-  while (true) {
-    if (pCSet == NULL && pNSet == NULL) break;
-
-    if (pCSet == NULL || (pNSet != NULL && pCSet->id > pNSet->id)) {
-      tsdbRemoveDFileSet(pNSet);
-
-      nidx++;
-      if (nidx < taosArrayGetSize(pFs->new->df)) {
-        pNSet = taosArrayGet(pFs->new->df, nidx);
-      } else {
-        pNSet = NULL;
-      }
-    } else if (pNSet == NULL || (pCSet != NULL && pCSet->id < pNSet->id)) {
-      cidx++;
-      if (cidx < taosArrayGetSize(pFs->curr->df)) {
-        pCSet = taosArrayGet(pFs->curr->df, cidx);
-      } else {
-        pCSet = NULL;
-      }
-    } else {
-      // TODO: apply dfileset change
-      nidx++;
-      if (nidx < taosArrayGetSize(pFs->new->df)) {
-        pNSet = taosArrayGet(pFs->new->df, nidx);
-      } else {
-        pNSet = NULL;
-      }
-
-      cidx++;
-      if (cidx < taosArrayGetSize(pFs->curr->df)) {
-        pCSet = taosArrayGet(pFs->curr->df, cidx);
-      } else {
-        pCSet = NULL;
-      }
-    }
+    pIter->fid = TSDB_IVLD_FID;
   }
 
-  return 0;
-}
-#endif
\ No newline at end of file
+  return pSet;
+}
\ No newline at end of file
diff --git a/src/tsdb/src/tsdbFile.c b/src/tsdb/src/tsdbFile.c
index 799eeb437b6e3b390852309e7baad6bc1a567082..53b36448c444126813a7ea4a858c93828a9547ac 100644
--- a/src/tsdb/src/tsdbFile.c
+++ b/src/tsdb/src/tsdbFile.c
@@ -58,6 +58,48 @@ void *tsdbDecodeSMFile(void *buf, SMFile *pMFile) {
   return buf;
 }
 
+int tsdbApplyMFileChange(SMFile *from, SMFile *to) {
+  ASSERT(from != NULL || to != NULL);
+
+  if (from != NULL) {
+    if (to == NULL) {
+      tsdbRemoveMFile(from);
+    } else {
+      if (tfsIsSameFile(TSDB_FILE_F(from), TSDB_FILE_F(to))) {
+        if (from->info.size > to->info.size) {
+          tsdbRollbackMFile(to);
+        }
+      } else {
+        tsdbRemoveMFile(from);
+      }
+    }
+  }
+
+  return 0;
+}
+
+static int tsdbRollBackMFile(const SMFile *pMFile) {
+  SMFile mf = *pMFile;
+
+  if (tsdbOpenMFile(&mf, O_WRONLY) < 0) {
+    return -1;
+  }
+
+  if (taosFtruncate(TSDB_FILE_FD(&mf), pMFile->info.size) < 0) {
+    terrno = TAOS_SYSTEM_ERROR(errno);
+    tsdbCloseMFile(&mf);
+    return -1;
+  }
+
+  if (tsdbUpdateMFileHeader(&mf) < 0) {
+    tsdbCloseMFile(&mf);
+    return -1;
+  }
+
+  tsdbCloseMFile(&mf);
+  return 0;
+}
+
 int tsdbCreateMFile(SMFile *pMFile) {
   ASSERT(pMFile->info.size == 0 && pMFile->info.magic == TSDB_FILE_INIT_MAGIC);
 
@@ -220,6 +262,48 @@ static void *tsdbDecodeDFInfo(void *buf, SDFInfo *pInfo) {
   return buf;
 }
 
+static int tsdbApplyDFileChange(SDFile *from, SDFile *to) {
+  ASSERT(from != NULL || to != NULL);
+
+  if (from != NULL) {
+    if (to == NULL) {
+      tsdbRemoveDFile(from);
+    } else {
+      if (tfsIsSameFile(TSDB_FILE_F(from), TSDB_FILE_F(to))) {
+        if (from->info.size > to->info.size) {
+          tsdbRollbackDFile(to);
+        }
+      } else {
+        tsdbRemoveDFile(from);
+      }
+    }
+  }
+
+  return 0;
+}
+
+static int tsdbRollBackDFile(const SDFile *pDFile) {
+  SDFile df = *pDFile;
+
+  if (tsdbOpenDFile(&df, O_WRONLY) < 0) {
+    return -1;
+  }
+
+  if (taosFtruncate(TSDB_FILE_FD(&df), pDFile->info.size) < 0) {
+    terrno = TAOS_SYSTEM_ERROR(errno);
+    tsdbCloseDFile(&df);
+    return -1;
+  }
+
+  if (tsdbUpdateDFileHeader(&df) < 0) {
+    tsdbCloseDFile(&df);
+    return -1;
+  }
+
+  tsdbCloseDFile(&df);
+  return 0;
+}
+
 // ============== Operations on SDFileSet
 void tsdbInitDFileSet(SDFileSet *pSet, SDiskID did, int vid, int fid, uint32_t ver) {
   pSet->fid = fid;
@@ -254,6 +338,16 @@ void *tsdbDecodeDFileSet(void *buf, SDFileSet *pSet) {
   return buf;
 }
 
+int tsdbApplyDFileSetChange(const SDFileSet *from, const SDFileSet *to) {
+  for (TSDB_FILE_T ftype = 0; ftype < TSDB_FILE_MAX; ftype++) {
+    if (tsdbApplyDFileChange(TSDB_DFILE_IN_SET(from, ftype), TSDB_DFILE_IN_SET(to, ftype)) < 0) {
+      return -1;
+    }
+  }
+
+  return 0;
+}
+
 int tsdbCreateDFileSet(SDFileSet *pSet) {
   for (TSDB_FILE_T ftype = 0; ftype < TSDB_FILE_MAX; ftype++) {
     if (tsdbCreateDFile(TSDB_DFILE_IN_SET(pSet, ftype)) < 0) {