diff --git a/source/libs/index/inc/index_cache.h b/source/libs/index/inc/index_cache.h
index 27f5a6fb20..0e7405869a 100644
--- a/source/libs/index/inc/index_cache.h
+++ b/source/libs/index/inc/index_cache.h
@@ -39,6 +39,7 @@ typedef struct IndexCache {
   int32_t    nTerm;
   int8_t     type;
 
+  pthread_mutex_t mtx;
 } IndexCache;
 
 #define CACHE_VERSION(cache) atomic_load_32(&cache->version)
@@ -71,7 +72,7 @@ void indexCacheUnRef(IndexCache* cache);
 
 void indexCacheDebug(IndexCache* cache);
 
-void indexCacheDestroySkiplist(SSkipList* slt);
+void indexCacheDestroyImm(IndexCache* cache);
 #ifdef __cplusplus
 }
 #endif
diff --git a/source/libs/index/src/index.c b/source/libs/index/src/index.c
index 23df5f9f9a..06e7e8ba44 100644
--- a/source/libs/index/src/index.c
+++ b/source/libs/index/src/index.c
@@ -436,9 +436,7 @@ int indexFlushCacheTFile(SIndex* sIdx, void* cache) {
     if (ret != 0) { indexError("faile to write into tindex "); }
   }
   // not free later, just put int table cache
-  SSkipList* timm = (SSkipList*)pCache->imm;
-  pCache->imm = NULL;  // or throw int bg thread
-  indexCacheDestroySkiplist(timm);
+  indexCacheDestroyImm(pCache);
 
   tfileWriteClose(tw);
   indexCacheIteratorDestroy(cacheIter);
diff --git a/source/libs/index/src/index_cache.c b/source/libs/index/src/index_cache.c
index 54aee8858b..3f99d04bc9 100644
--- a/source/libs/index/src/index_cache.c
+++ b/source/libs/index/src/index_cache.c
@@ -20,7 +20,7 @@
 
 #define MAX_INDEX_KEY_LEN 256  // test only, change later
 
-#define CACH_LIMIT 1000000
+#define MEM_TERM_LIMIT 1000000
 // ref index_cache.h:22
 //#define CACHE_KEY_LEN(p) \
 //  (sizeof(int32_t) + sizeof(uint16_t) + sizeof(p->colType) + sizeof(p->nColVal) + p->nColVal + sizeof(uint64_t) + sizeof(p->operType))
@@ -78,6 +78,7 @@ IndexCache* indexCacheCreate(SIndex* idx, const char* colName, int8_t type) {
   cache->index = idx;
   cache->version = 0;
 
+  pthread_mutex_init(&cache->mtx, NULL);
   indexCacheRef(cache);
   return cache;
 }
@@ -103,13 +104,21 @@ void indexCacheDestroySkiplist(SSkipList* slt) {
   }
   tSkipListDestroyIter(iter);
 }
+void indexCacheDestroyImm(IndexCache* cache) {
+  pthread_mutex_lock(&cache->mtx);
+  SSkipList* timm = (SSkipList*)cache->imm;
+  cache->imm = NULL;  // or throw int bg thread
+  pthread_mutex_unlock(&cache->mtx);
 
+  indexCacheDestroySkiplist(timm);
+}
 void indexCacheDestroy(void* cache) {
   IndexCache* pCache = cache;
   if (pCache == NULL) { return; }
   tSkipListDestroy(pCache->mem);
   tSkipListDestroy(pCache->imm);
   free(pCache->colName);
+
   free(pCache);
 }
 
@@ -170,6 +179,27 @@ int indexCacheSchedToMerge(IndexCache* pCache) {
 
   taosScheduleTask(indexQhandle, &schedMsg);
 }
+static void indexCacheMakeRoomForWrite(IndexCache* cache) {
+  while (true) {
+    if (cache->nTerm < MEM_TERM_LIMIT) {
+      cache->nTerm += 1;
+      break;
+    } else if (cache->imm != NULL) {
+      // TODO: wake up by condition variable
+      pthread_mutex_unlock(&cache->mtx);
+      taosMsleep(50);
+      pthread_mutex_lock(&cache->mtx);
+    } else {
+      cache->imm = cache->mem;
+      cache->mem = indexInternalCacheCreate(cache->type);
+      cache->nTerm = 1;
+      // sched to merge
+      // unref cache in bgwork
+      indexCacheSchedToMerge(cache);
+    }
+  }
+}
+
 int indexCachePut(void* cache, SIndexTerm* term, uint64_t uid) {
   if (cache == NULL) { return -1; }
 
@@ -188,23 +218,12 @@ int indexCachePut(void* cache, SIndexTerm* term, uint64_t uid) {
   ct->uid = uid;
   ct->operaType = term->operType;
 
+  // ugly code, refactor later
+  pthread_mutex_lock(&pCache->mtx);
+  indexCacheMakeRoomForWrite(pCache);
   tSkipListPut(pCache->mem, (char*)ct);
-  pCache->nTerm += 1;
+  pthread_mutex_unlock(&pCache->mtx);
 
-  if (pCache->nTerm >= CACH_LIMIT) {
-    pCache->nTerm = 0;
-
-    while (pCache->imm != NULL) {
-      // do nothong
-    }
-
-    pCache->imm = pCache->mem;
-    pCache->mem = indexInternalCacheCreate(pCache->type);
-
-    // sched to merge
-    // unref cache int bgwork
-    indexCacheSchedToMerge(pCache);
-  }
   indexCacheUnRef(pCache);
   return 0;
   // encode end