change gen first tag name

source/dnode/mnode/impl/src/mndStb.c

@@ -868,6 +868,9 @@ static int32_t mndGenIdxNameForFirstTag(char *fullname, char *dbname, char *tagn
     int8_t end = left >= 24 ? 24 : left - 1;
     // gen rand str len [base:end]
     // note: ignore rand performance issues
+
+    taosSeedRand(taosSafeRand());
+
     int64_t len = taosRand() % (end - start + 1) + start;
     taosRandStr2(randStr, len);
     sprintf(fullname, "%s.%s_%s", dbname, tagname, randStr);

source/os/src/osRand.c

@@ -86,8 +86,7 @@ void taosRandStr(char* str, int32_t size) {
 }
 
 void taosRandStr2(char* str, int32_t size) {
-
-  const char* set = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ@";
+  const char* set = "abcdefghijklmnopqrstuvwxyz0123456789@";
   int32_t     len = strlen(set);
 
   for (int32_t i = 0; i < size; ++i) {