fix(query): add query cache implementation file

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

+/*
+ * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
+ *
+ * This program is free software: you can use, redistribute, and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3
+ * or later ("AGPL"), as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "taoserror.h"
+#include "tarray.h"
+#include "tcommon.h"
+#include "tsdb.h"
+
+#define LASTROW_RETRIEVE_TYPE_ALL        0x1
+#define LASTROW_RETRIEVE_TYPE_SINGLE     0x2
+
+// todo parse the stsrow and set the results
+static void keepOneRow(const STSRow* pRow, SSDataBlock* pBlock) {
+  int32_t rowIndex = pBlock->info.rows;
+  size_t  numOfCols = taosArrayGetSize(pBlock->pDataBlock);
+  for (int32_t i = 0; i < numOfCols; ++i) {
+    SColumnInfoData* pColInfoData = taosArrayGet(pBlock->pDataBlock, i);
+
+    // todo extract the value of specified column id from STSRow
+    const char* p = NULL;
+    colDataAppend(pColInfoData, rowIndex, p, false);
+  }
+
+  pBlock->info.rows += 1;
+}
+
+int32_t tsdbRetrieveLastRow(void* pVnode, const SArray* pTableIdList, int32_t type, SSDataBlock* pResBlock) {
+  if (pVnode == NULL || pTableIdList == NULL || pResBlock == NULL) {
+    return TSDB_CODE_INVALID_PARA;
+  }
+
+  SVnode* pv = pVnode;
+  STSRow* pRow = NULL;
+  size_t numOfTables = taosArrayGetSize(pTableIdList);
+
+  // retrieve the only one last row of all tables in the uid list.
+  if (type == LASTROW_RETRIEVE_TYPE_SINGLE) {
+    int64_t lastKey = INT64_MIN;
+    bool    internalResult = false;
+    for (int32_t i = 0; i < numOfTables; ++i) {
+      tb_uid_t* uid = taosArrayGet(pTableIdList, i);
+
+      int32_t code = tsdbCacheGetLastrow(pv->pTsdb->lruCache, *uid, &pRow);
+      if (code != TSDB_CODE_SUCCESS) {
+        return code;
+      }
+
+      if (pRow == NULL) {
+        continue;
+      }
+
+      if (pRow->ts > lastKey) {
+        // Set result row into the same rowIndex repeatly, so we need to check if the internal result row has already
+        // appended or not.
+        if (internalResult) {
+          pResBlock->info.rows -= 1;
+        }
+
+        keepOneRow(pRow, pResBlock);
+        internalResult = true;
+        lastKey = pRow->ts;
+      }
+    }
+  } else if (type == LASTROW_RETRIEVE_TYPE_ALL) {
+    for (int32_t i = 0; i < numOfTables; ++i) {
+      tb_uid_t* uid = taosArrayGet(pTableIdList, i);
+
+      int32_t code = tsdbCacheGetLastrow(pv->pTsdb->lruCache, *uid, &pRow);
+      if (code != TSDB_CODE_SUCCESS) {
+        return code;
+      }
+
+      // no data in the table of Uid
+      if (pRow == NULL) {
+        continue;
+      }
+
+      keepOneRow(pRow, pResBlock);
+    }
+  } else {
+    return TSDB_CODE_INVALID_PARA;
+  }
+
+  return TSDB_CODE_SUCCESS;
+}