[TD-10870]<enhance>: [schemaless]add a NULL tag to accommodate influxDB tag is optional

src/client/src/tscParseLineProtocol.c

@@ -245,16 +245,19 @@ static int32_t buildDataPointSchemas(TAOS_SML_DATA_POINT* points, int numPoint,
       if (!point->childTableName) {
         buildSmlChildTableName(point, info);
       }
-      const char tagNullName[] = "`_tag_null`";
-      size_t* pTagNullIdx = taosHashGet(pStableSchema->tagHash, tagNullName, strlen(tagNullName));
+      char tagNullName[TSDB_COL_NAME_LEN] = {0};
+      int16_t nameLen = strlen(tsSmlTagNullName);
+      strncpy(tagNullName, tsSmlTagNullName, nameLen);
+      addEscapeCharToString(tagNullName, nameLen);
+      size_t* pTagNullIdx = taosHashGet(pStableSchema->tagHash, tagNullName, nameLen + TS_ESCAPE_CHAR_SIZE);
       if (!pTagNullIdx) {
         SSchema tagNull = {0};
         tagNull.type  = TSDB_DATA_TYPE_NCHAR;
-        tagNull.bytes = 6;
-        strncpy(tagNull.name, tagNullName, strlen(tagNullName));
+        tagNull.bytes = TSDB_NCHAR_SIZE + VARSTR_HEADER_SIZE;
+        strncpy(tagNull.name, tagNullName, nameLen + TS_ESCAPE_CHAR_SIZE);
         taosArrayPush(pStableSchema->tags, &tagNull);
         size_t tagNullIdx = taosArrayGetSize(pStableSchema->tags) - 1;
-        taosHashPut(pStableSchema->tagHash, tagNull.name, strlen(tagNullName), &tagNullIdx, sizeof(tagNullIdx));
+        taosHashPut(pStableSchema->tagHash, tagNull.name, nameLen + TS_ESCAPE_CHAR_SIZE, &tagNullIdx, sizeof(tagNullIdx));
       }
     }
 

src/common/inc/tglobal.h

@@ -237,6 +237,7 @@ extern int8_t tsDeadLockKillQuery;
 // schemaless
 extern char tsDefaultJSONStrType[];
 extern char tsSmlChildTableName[];
+extern char tsSmlTagNullName[];
 
 
 typedef struct {

src/common/src/tglobal.c

@@ -291,7 +291,11 @@ int8_t tsDeadLockKillQuery = 0;
 
 // default JSON string type
 char tsDefaultJSONStrType[7] = "nchar";
-char tsSmlChildTableName[TSDB_TABLE_NAME_LEN] = ""; //user defined child table name can be specified in tag value. If set to empty system will generate table name using MD5 hash.
+char tsSmlChildTableName[TSDB_TABLE_NAME_LEN] = ""; //user defined child table name can be specified in tag value.
+                                                    //If set to empty system will generate table name using MD5 hash.
+char tsSmlTagNullName[TSDB_COL_NAME_LEN] = "_tag_null"; //for line protocol if tag is omitted, add a tag with NULL value
+                                                        //to make sure inserted records belongs to the same measurement
+                                                        //default name is _tag_null and can be user configurable
 
 int32_t (*monStartSystemFp)() = NULL;
 void (*monStopSystemFp)() = NULL;
@@ -1701,6 +1705,17 @@ static void doInitGlobalConfig(void) {
   cfg.unitType = TAOS_CFG_UTYPE_NONE;
   taosInitConfigOption(cfg);
 
+  // name for a NULL value tag added for Line Protocol when tag fields are omitted
+  cfg.option = "smlTagNullName";
+  cfg.ptr = tsSmlTagNullName;
+  cfg.valType = TAOS_CFG_VTYPE_STRING;
+  cfg.cfgType = TSDB_CFG_CTYPE_B_CONFIG | TSDB_CFG_CTYPE_B_SHOW | TSDB_CFG_CTYPE_B_CLIENT;
+  cfg.minValue = 0;
+  cfg.maxValue = 0;
+  cfg.ptrLength = tListLen(tsSmlTagNullName);
+  cfg.unitType = TAOS_CFG_UTYPE_NONE;
+  taosInitConfigOption(cfg);
+
   // flush vnode wal file if walSize > walFlushSize and walSize > cache*0.5*blocks
   cfg.option = "walFlushSize";
   cfg.ptr = &tsdbWalFlushSize;