cache/reader: move pLastCols into single block

source/dnode/vnode/src/tsdb/tsdbCacheRead.c

@@ -277,7 +277,6 @@ int32_t tsdbRetrieveCacheRows(void* pReader, SSDataBlock* pResBlock, const int32
   int32_t           code = TSDB_CODE_SUCCESS;
   SArray*           pRow = taosArrayInit(TARRAY_SIZE(pr->pCidList), sizeof(SLastCol));
   bool              hasRes = false;
-  SArray*           pLastCols = NULL;
 
   void** pRes = taosMemoryCalloc(pr->numOfCols, POINTER_BYTES);
   if (pRes == NULL) {
@@ -293,7 +292,18 @@ int32_t tsdbRetrieveCacheRows(void* pReader, SSDataBlock* pResBlock, const int32
     p->ts = INT64_MIN;
   }
 
-  pLastCols = taosArrayInit(pr->numOfCols, sizeof(SLastCol));
+  taosThreadMutexLock(&pr->readerMutex);
+  code = tsdbTakeReadSnap2((STsdbReader*)pr, tsdbCacheQueryReseek, &pr->pReadSnap);
+  if (code != TSDB_CODE_SUCCESS) {
+    goto _end;
+  }
+
+  int8_t         ltype = (pr->type & CACHESCAN_RETRIEVE_LAST) >> 3;
+  STableKeyInfo* pTableList = pr->pTableList;
+
+  // retrieve the only one last row of all tables in the uid list.
+  if (HASTYPE(pr->type, CACHESCAN_RETRIEVE_TYPE_SINGLE)) {
+    SArray* pLastCols = taosArrayInit(pr->numOfCols, sizeof(SLastCol));
     if (pLastCols == NULL) {
       code = TSDB_CODE_OUT_OF_MEMORY;
       goto _end;
@@ -310,17 +320,6 @@ int32_t tsdbRetrieveCacheRows(void* pReader, SSDataBlock* pResBlock, const int32
       taosArrayPush(pLastCols, &p);
     }
 
-  taosThreadMutexLock(&pr->readerMutex);
-  code = tsdbTakeReadSnap2((STsdbReader*)pr, tsdbCacheQueryReseek, &pr->pReadSnap);
-  if (code != TSDB_CODE_SUCCESS) {
-    goto _end;
-  }
-
-  int8_t         ltype = (pr->type & CACHESCAN_RETRIEVE_LAST) >> 3;
-  STableKeyInfo* pTableList = pr->pTableList;
-
-  // retrieve the only one last row of all tables in the uid list.
-  if (HASTYPE(pr->type, CACHESCAN_RETRIEVE_TYPE_SINGLE)) {
     int64_t st = taosGetTimestampUs();
     int64_t totalLastTs = INT64_MAX;
     for (int32_t i = 0; i < pr->numOfTables; ++i) {
@@ -398,6 +397,8 @@ int32_t tsdbRetrieveCacheRows(void* pReader, SSDataBlock* pResBlock, const int32
     if (hasRes) {
       saveOneRow(pLastCols, pResBlock, pr, slotIds, dstSlotIds, pRes, pr->idstr);
     }
+
+    taosArrayDestroyEx(pLastCols, freeItem);
   } else if (HASTYPE(pr->type, CACHESCAN_RETRIEVE_TYPE_ALL)) {
     for (int32_t i = pr->tableIndex; i < pr->numOfTables; ++i) {
       tb_uid_t uid = pTableList[i].uid;
@@ -440,7 +441,6 @@ _end:
 
   taosMemoryFree(pRes);
   taosArrayDestroy(pRow);
-  taosArrayDestroyEx(pLastCols, freeItem);
 
   return code;
 }