Implement MarkM optimization request to avoid redundnat packet exchange

in cursors.


libmysql/libmysql.c:
  - reset_stmt_handle(): don't reset the server side just because we have 
    an open cursor: the server will close the cursor automatically if 
    needed
sql/sql_prepare.cc:
  - implement Prepared_statement::close_cursor,
  - implicitly close an open cursor in mysql_stmt_execute instead of 
    issuing an error (to reduce the need to explicitly close cursors
    and save network bandwidth).
  - cleanup
sql/sql_select.cc:
  Remove a destructor: cursor destruction can not be done by simply
  calling a destructor, because of cross-references between cursor
  and statement memory.
sql/sql_select.h:
  - add an empty Cursor destructor
tests/mysql_client_test.c:
  - remove a test for dropped functionality

libmysql/libmysql.c

@@ -4907,13 +4907,12 @@ static my_bool reset_stmt_handle(MYSQL_STMT *stmt, uint flags)
   {
     MYSQL *mysql= stmt->mysql;
     MYSQL_DATA *result= &stmt->result;
-    my_bool has_cursor= stmt->read_row_func == stmt_read_row_from_cursor;
 
     /*
       Reset stored result set if so was requested or it's a part
       of cursor fetch.
     */
-    if (result->data && (has_cursor || (flags & RESET_STORE_RESULT)))
+    if (result->data && (flags & RESET_STORE_RESULT))
     {
       /* Result buffered */
       free_root(&result->alloc, MYF(MY_KEEP_PREALLOC));
@@ -4944,7 +4943,7 @@ static my_bool reset_stmt_handle(MYSQL_STMT *stmt, uint flags)
           mysql->status= MYSQL_STATUS_READY;
         }
       }
-      if (has_cursor || (flags & RESET_SERVER_SIDE))
+      if (flags & RESET_SERVER_SIDE)
       {
         /*
           Reset the server side statement and close the server side

sql/sql_prepare.cc

@@ -106,6 +106,7 @@ class Prepared_statement: public Statement
   virtual ~Prepared_statement();
   void setup_set_params();
   virtual Query_arena::Type type() const;
+  virtual void close_cursor();
 };
 
 static void execute_stmt(THD *thd, Prepared_statement *stmt,
@@ -1986,10 +1987,7 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
 
   cursor= stmt->cursor;
   if (cursor && cursor->is_open())
-  {
-    my_error(ER_EXEC_STMT_WITH_OPEN_CURSOR, MYF(0));
-    DBUG_VOID_RETURN;
-  }
+    stmt->close_cursor();
 
   DBUG_ASSERT(thd->free_list == NULL);
   mysql_reset_thd_for_next_command(thd);
@@ -2284,6 +2282,7 @@ void mysql_stmt_reset(THD *thd, char *packet)
   if (!(stmt= find_prepared_statement(thd, stmt_id, "mysql_stmt_reset")))
     DBUG_VOID_RETURN;
 
+  stmt->close_cursor();                    /* will reset statement params */
   cursor= stmt->cursor;
   if (cursor && cursor->is_open())
   {
@@ -2295,12 +2294,6 @@ void mysql_stmt_reset(THD *thd, char *packet)
 
   stmt->state= Query_arena::PREPARED;
 
-  /*
-    Clear parameters from data which could be set by
-    mysql_stmt_send_long_data() call.
-  */
-  reset_stmt_params(stmt);
-
   mysql_reset_thd_for_next_command(thd);
   send_ok(thd);
 
@@ -2448,10 +2441,17 @@ void Prepared_statement::setup_set_params()
 Prepared_statement::~Prepared_statement()
 {
   if (cursor)
+  {
+    if (cursor->is_open())
+    {
+      cursor->close(FALSE);
+      free_items();
+      free_root(cursor->mem_root, MYF(0));
+    }
     cursor->Cursor::~Cursor();
-  free_items();
-  if (cursor)
-    free_root(cursor->mem_root, MYF(0));
+  }
+  else
+    free_items();
   delete lex->result;
 }
 
@@ -2460,3 +2460,20 @@ Query_arena::Type Prepared_statement::type() const
 {
   return PREPARED_STATEMENT;
 }
+
+
+void Prepared_statement::close_cursor()
+{
+  if (cursor && cursor->is_open())
+  {
+    thd->change_list= cursor->change_list;
+    cursor->close(FALSE);
+    cleanup_stmt_and_thd_after_use(this, thd);
+    free_root(cursor->mem_root, MYF(0));
+  }
+  /*
+    Clear parameters from data which could be set by
+    mysql_stmt_send_long_data() call.
+  */
+  reset_stmt_params(this);
+}

sql/sql_select.cc

@@ -1915,12 +1915,6 @@ Cursor::close(bool is_active)
 }
 
 
-Cursor::~Cursor()
-{
-  if (is_open())
-    close(FALSE);
-}
-
 /*********************************************************************/
 
 /*

sql/sql_select.h

@@ -408,7 +408,7 @@ class Cursor: public Sql_alloc, public Query_arena
 
   void set_unit(SELECT_LEX_UNIT *unit_arg) { unit= unit_arg; }
   Cursor(THD *thd);
-  ~Cursor();
+  ~Cursor() {}
 };
 
 

tests/mysql_client_test.c

@@ -13050,27 +13050,6 @@ static void test_bug9478()
     check_execute(stmt, rc);
     if (!opt_silent && i == 0)
       printf("Fetched row: %s\n", a);
-    /*
-      Although protocol-wise an attempt to execute a statement which
-      already has an open cursor associated with it will yield an error,
-      the client library behavior tested here is consistent with
-      the non-cursor execution scenario: mysql_stmt_execute will
-      silently close the cursor if necessary.
-    */
-    {
-      char buff[9];
-      /* Fill in the execute packet */
-      int4store(buff, stmt->stmt_id);
-      buff[4]= 0;                               /* Flag */
-      int4store(buff+5, 1);                     /* Reserved for array bind */
-      rc= ((*mysql->methods->advanced_command)(mysql, COM_STMT_EXECUTE, buff,
-                                               sizeof(buff), 0,0,1) ||
-           (*mysql->methods->read_query_result)(mysql));
-      DIE_UNLESS(rc);
-      if (!opt_silent && i == 0)
-        printf("Got error (as expected): %s\n", mysql_error(mysql));
-    }
-
     rc= mysql_stmt_execute(stmt);
     check_execute(stmt, rc);
 
@@ -13429,7 +13408,7 @@ static void test_bug10794()
   bind[1].length= &a_len;
   rc= mysql_stmt_bind_param(stmt, bind);
   check_execute(stmt, rc);
-  for (i= 0; i < 34; i++)
+  for (i= 0; i < 42; i++)
   {
     id_val= (i+1)*10;
     sprintf(a, "a%d", i);