enh(query): enable the limit clause to be push down to the table scan operator.

source/libs/executor/inc/executorimpl.h

@@ -318,12 +318,11 @@ typedef struct {
 typedef struct STableScanInfo {
   STsdbReader*           dataReader;
   SReadHandle            readHandle;
-
+  SLimitInfo             limitInfo;
   SFileBlockLoadRecorder readRecorder;
   SScanInfo              scanInfo;
   int32_t                scanTimes;
   SNode*                 pFilterNode;  // filter info, which is push down by optimizer
-
   SSDataBlock*           pResBlock;
   SColMatchInfo          matchInfo;
   SExprSupp              pseudoSup;
@@ -334,7 +333,6 @@ typedef struct STableScanInfo {
   int32_t                currentGroupId;
   int32_t                currentTable;
   int8_t                 scanMode;
-  int8_t               noTable;
   SAggOptrPushDownInfo   pdInfo;
   int8_t                 assignBlockUid;
 } STableScanInfo;

source/libs/executor/src/projectoperator.c

@@ -210,8 +210,6 @@ SSDataBlock* doProjectOperation(SOperatorInfo* pOperator) {
     pOperator->status = OP_OPENED;
   }
 
-  qDebug("enter project");
-
   if (pOperator->status == OP_EXEC_DONE) {
     if (pTaskInfo->execModel == OPTR_EXEC_MODEL_QUEUE) {
       pOperator->status = OP_OPENED;

source/libs/executor/src/scanoperator.c

@@ -364,6 +364,7 @@ static int32_t loadDataBlock(SOperatorInfo* pOperator, STableScanInfo* pTableSca
 
   pCost->totalBlocks += 1;
   pCost->totalRows += pBlock->info.rows;
+
   bool loadSMA = false;
 
   *status = pInfo->dataBlockLoadFlag;
@@ -379,6 +380,7 @@ static int32_t loadDataBlock(SOperatorInfo* pOperator, STableScanInfo* pTableSca
     qDebug("%s data block filter out, brange:%" PRId64 "-%" PRId64 ", rows:%d", GET_TASKID(pTaskInfo),
            pBlockInfo->window.skey, pBlockInfo->window.ekey, pBlockInfo->rows);
     pCost->filterOutBlocks += 1;
+    pCost->totalRows += pBlock->info.rows;
     return TSDB_CODE_SUCCESS;
   } else if (*status == FUNC_DATA_REQUIRED_NOT_LOAD) {
     qDebug("%s data block skipped, brange:%" PRId64 "-%" PRId64 ", rows:%d", GET_TASKID(pTaskInfo),
@@ -447,6 +449,10 @@ static int32_t loadDataBlock(SOperatorInfo* pOperator, STableScanInfo* pTableSca
   doSetTagColumnData(pTableScanInfo, pBlock, pTaskInfo);
 
   if (pTableScanInfo->pFilterNode != NULL) {
+
+    // restore the previous value
+    pCost->totalRows -= pBlock->info.rows;
+
     int64_t st = taosGetTimestampUs();
     doFilter(pTableScanInfo->pFilterNode, pBlock, &pTableScanInfo->matchInfo, pOperator->exprSupp.pFilterInfo);
 
@@ -460,6 +466,22 @@ static int32_t loadDataBlock(SOperatorInfo* pOperator, STableScanInfo* pTableSca
     } else {
       qDebug("%s data block filter applied, elapsed time:%.2f ms", GET_TASKID(pTaskInfo), el);
     }
+
+    pCost->totalRows += pBlock->info.rows;
+  }
+
+  pInfo->limitInfo.numOfOutputRows = pCost->totalRows;
+  SLimit* pLimit = &pInfo->limitInfo.limit;
+
+  if (pLimit->limit != -1 && pLimit->limit < pInfo->limitInfo.numOfOutputRows && pBlock->info.rows > 0) {
+    // limit the output rows
+    int32_t overflowRows = pInfo->limitInfo.numOfOutputRows - pLimit->limit;
+    int32_t keep = pBlock->info.rows - overflowRows;
+
+    blockDataKeepFirstNRows(pBlock, keep);
+    qDebug("output limit %"PRId64" has reached, %s", pLimit->limit, GET_TASKID(pTaskInfo));
+    setTaskStatus(pTaskInfo, TASK_COMPLETED);
+    pOperator->status = OP_EXEC_DONE;
   }
 
   return TSDB_CODE_SUCCESS;
@@ -691,10 +713,6 @@ static SSDataBlock* doTableScan(SOperatorInfo* pOperator) {
 
   // if scan table by table
   if (pInfo->scanMode == TABLE_SCAN__TABLE_ORDER) {
-    if (pInfo->noTable) {
-      return NULL;
-    }
-
     int32_t numOfTables = taosArrayGetSize(pTaskInfo->tableqinfoList.pTableList);
 
     while (1) {
@@ -727,7 +745,6 @@ static SSDataBlock* doTableScan(SOperatorInfo* pOperator) {
     }
 
     SArray* tableList = taosArrayGetP(pTaskInfo->tableqinfoList.pGroupList, pInfo->currentGroupId);
-
     tsdbReaderClose(pInfo->dataReader);
 
     int32_t code = tsdbReaderOpen(pInfo->readHandle.vnode, &pInfo->cond, tableList, (STsdbReader**)&pInfo->dataReader,
@@ -749,9 +766,6 @@ static SSDataBlock* doTableScan(SOperatorInfo* pOperator) {
     return NULL;
   }
 
-  SArray* tableList = taosArrayGetP(pTaskInfo->tableqinfoList.pGroupList, pInfo->currentGroupId);
-  //  tsdbSetTableList(pInfo->dataReader, tableList);
-
   tsdbReaderReset(pInfo->dataReader, &pInfo->cond);
   pInfo->scanTimes = 0;
 
@@ -798,9 +812,15 @@ SOperatorInfo* createTableScanOperatorInfo(STableScanPhysiNode* pTableScanNode,
   }
 
   SDataBlockDescNode* pDescNode = pTableScanNode->scan.node.pOutputDataBlockDesc;
+
   int32_t numOfCols = 0;
   int32_t code = extractColMatchInfo(pTableScanNode->scan.pScanCols, pDescNode, &numOfCols, COL_MATCH_FROM_COL_ID,
                                      &pInfo->matchInfo);
+  if (code != TSDB_CODE_SUCCESS) {
+    goto _error;
+  }
+
+  initLimitInfo(pTableScanNode->scan.node.pLimit, pTableScanNode->scan.node.pSlimit, &pInfo->limitInfo);
 
   code = initQueryTableDataCond(&pInfo->cond, pTableScanNode);
   if (code != TSDB_CODE_SUCCESS) {
@@ -825,6 +845,9 @@ SOperatorInfo* createTableScanOperatorInfo(STableScanPhysiNode* pTableScanNode,
 
   if (pInfo->pFilterNode != NULL) {
     code = filterInitFromNode((SNode*)pInfo->pFilterNode, &pOperator->exprSupp.pFilterInfo, 0);
+    if (code != TSDB_CODE_OUT_OF_MEMORY) {
+      goto _error;
+    }
   }
 
   pInfo->scanFlag = MAIN_SCAN;

source/libs/planner/src/planOptimizer.c

@@ -2498,7 +2498,7 @@ static const SOptimizeRule optimizeRuleSet[] = {
   {.pName = "RewriteUnique",              .optimizeFunc = rewriteUniqueOptimize},
   {.pName = "LastRowScan",                .optimizeFunc = lastRowScanOptimize},
   {.pName = "TagScan",                    .optimizeFunc = tagScanOptimize},
-  // {.pName = "PushDownLimit",              .optimizeFunc = pushDownLimitOptimize}
+  {.pName = "PushDownLimit",              .optimizeFunc = pushDownLimitOptimize}
 };
 // clang-format on