MDEV-4260 Don't create frm files for temporary tables

* Don't write frm for tmp tables
* pass frm image down to open_table_uncached, when possible
* don't use truncate-by-recreate for temp tables - cannot recreate
  without frm, and delete_all_rows is faster anyway

mysql-test/r/temp_table_frm.result

+create table t1 select * from information_schema.session_status where variable_name like 'Opened%';
+create temporary table t2 (a int) engine=memory;
+select variable_name, session_status.variable_value - t1.variable_value
+from information_schema.session_status join t1 using (variable_name);
+variable_name	session_status.variable_value - t1.variable_value
+OPENED_FILES	0
+OPENED_PLUGIN_LIBRARIES	0
+OPENED_TABLE_DEFINITIONS	2
+OPENED_TABLES	2
+OPENED_VIEWS	0
+truncate table t2;
+select variable_name, session_status.variable_value - t1.variable_value
+from information_schema.session_status join t1 using (variable_name);
+variable_name	session_status.variable_value - t1.variable_value
+OPENED_FILES	0
+OPENED_PLUGIN_LIBRARIES	0
+OPENED_TABLE_DEFINITIONS	2
+OPENED_TABLES	2
+OPENED_VIEWS	0
+drop table t1;

mysql-test/t/temp_table_frm.test

+#
+# MDEV-4260 Don't create frm files for temporary tables
+#
+create table t1 select * from information_schema.session_status where variable_name like 'Opened%';
+create temporary table t2 (a int) engine=memory;
+select variable_name, session_status.variable_value - t1.variable_value
+from information_schema.session_status join t1 using (variable_name);
+let $tmpdir= `select @@tmpdir`;
+--list_files $tmpdir/
+truncate table t2;
+select variable_name, session_status.variable_value - t1.variable_value
+from information_schema.session_status join t1 using (variable_name);
+drop table t1;

sql/sql_base.cc

@@ -5508,6 +5508,7 @@ void close_tables_for_reopen(THD *thd, TABLE_LIST **tables,
   @param thd                          Thread context.
   @param hton                         Storage engine of the table, if known,
                                       or NULL otherwise.
+  @param frm                          frm image
   @param path                         Path (without .frm)
   @param db                           Database name.
   @param table_name                   Table name.
@@ -5527,6 +5528,7 @@ void close_tables_for_reopen(THD *thd, TABLE_LIST **tables,
 */
 
 TABLE *open_table_uncached(THD *thd, handlerton *hton,
+                           LEX_CUSTRING *frm,
                            const char *path, const char *db,
                            const char *table_name,
                            bool add_to_temporary_tables_list,
@@ -5561,7 +5563,17 @@ TABLE *open_table_uncached(THD *thd, handlerton *hton,
                        strend(saved_cache_key)+1, tmp_path);
   share->db_plugin= ha_lock_engine(thd, hton);
 
-  if (open_table_def(thd, share, GTS_TABLE | GTS_USE_DISCOVERY))
+  /*
+    Use the frm image, if possible, open the file otherwise.
+
+    The image might be unavailable in ALTER TABLE, when the discovering
+    engine took over the ownership (see TABLE::read_frm_image).
+  */
+  int res= frm->str
+    ? share->init_from_binary_frm_image(thd, false, frm->str, frm->length)
+    : open_table_def(thd, share, GTS_TABLE | GTS_USE_DISCOVERY);
+
+  if (res)
   {
     /* No need to lock share->mutex as this is not needed for tmp tables */
     free_table_share(share);

sql/sql_base.h

@@ -127,7 +127,8 @@ bool open_new_frm(THD *thd, TABLE_SHARE *share, const char *alias,
 
 bool get_key_map_from_key_list(key_map *map, TABLE *table,
                                List<String> *index_list);
-TABLE *open_table_uncached(THD *thd, handlerton *hton, const char *path,
+TABLE *open_table_uncached(THD *thd, handlerton *hton,
+                           LEX_CUSTRING *frm, const char *path,
                            const char *db, const char *table_name,
                            bool add_to_temporary_tables_list,
                            bool open_in_engine);

sql/sql_table.cc

@@ -4847,7 +4847,7 @@ int create_table_impl(THD *thd,
       THD::temporary_tables list.
     */
 
-    TABLE *table= open_table_uncached(thd, create_info->db_type, path,
+    TABLE *table= open_table_uncached(thd, create_info->db_type, frm, path,
                                       db, table_name, true, true);
 
     if (!table)
@@ -8691,7 +8691,7 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
     // We assume that the table is non-temporary.
     DBUG_ASSERT(!table->s->tmp_table);
 
-    if (!(altered_table= open_table_uncached(thd, new_db_type,
+    if (!(altered_table= open_table_uncached(thd, new_db_type, &frm,
                                              alter_ctx.get_tmp_path(),
                                              alter_ctx.new_db,
                                              alter_ctx.tmp_name,
@@ -8845,7 +8845,7 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
 
   if (create_info->tmp_table())
   {
-    if (!open_table_uncached(thd, new_db_type,
+    if (!open_table_uncached(thd, new_db_type, &frm,
                              alter_ctx.get_tmp_path(),
                              alter_ctx.new_db, alter_ctx.tmp_name,
                              true, true))
@@ -8867,7 +8867,8 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
   {
     /* table is a normal table: Create temporary table in same directory */
     /* Open our intermediate table. */
-    new_table= open_table_uncached(thd, new_db_type, alter_ctx.get_tmp_path(),
+    new_table= open_table_uncached(thd, new_db_type, &frm,
+                                   alter_ctx.get_tmp_path(),
                                    alter_ctx.new_db, alter_ctx.tmp_name,
                                    true, true);
   }

sql/sql_truncate.cc

@@ -261,52 +261,6 @@ Sql_cmd_truncate_table::handler_truncate(THD *thd, TABLE_LIST *table_ref,
 }
 
 
-/*
-  Close and recreate a temporary table. In case of success,
-  write truncate statement into the binary log if in statement
-  mode.
-
-  @param  thd     Thread context.
-  @param  table   The temporary table.
-
-  @retval  FALSE  Success.
-  @retval  TRUE   Error.
-*/
-
-static bool recreate_temporary_table(THD *thd, TABLE *table)
-{
-  bool error= TRUE;
-  TABLE_SHARE *share= table->s;
-  handlerton *table_type= table->s->db_type();
-  TABLE *new_table;
-  DBUG_ENTER("recreate_temporary_table");
-
-  table->file->info(HA_STATUS_AUTO | HA_STATUS_NO_LOCK);
-
-  /* Don't free share. */
-  close_temporary_table(thd, table, FALSE, FALSE);
-
-  dd_recreate_table(thd, share->db.str, share->table_name.str,
-                    share->normalized_path.str);
-
-  if ((new_table= open_table_uncached(thd, table_type, share->path.str,
-                                      share->db.str,
-                                      share->table_name.str, true, true)))
-  {
-    error= FALSE;
-    thd->thread_specific_used= TRUE;
-    new_table->s->table_creation_was_logged= share->table_creation_was_logged;
-  }
-  else
-    rm_temporary_table(table_type, share->path.str);
-
-  free_table_share(share);
-  my_free(table);
-
-  DBUG_RETURN(error);
-}
-
-
 /*
   Handle locking a base table for truncate.
 
@@ -441,30 +395,10 @@ bool Sql_cmd_truncate_table::truncate_table(THD *thd, TABLE_LIST *table_ref)
   /* If it is a temporary table, no need to take locks. */
   if (is_temporary_table(table_ref))
   {
-    TABLE *tmp_table= table_ref->table;
-
     /* In RBR, the statement is not binlogged if the table is temporary. */
     binlog_stmt= !thd->is_current_stmt_binlog_format_row();
 
-    /* Note that a temporary table cannot be partitioned. */
-    if (ha_check_storage_engine_flag(tmp_table->s->db_type(),
-                                     HTON_CAN_RECREATE))
-    {
-      if ((error= recreate_temporary_table(thd, tmp_table)))
-        binlog_stmt= FALSE; /* No need to binlog failed truncate-by-recreate. */
-
-      DBUG_ASSERT(! thd->transaction.stmt.modified_non_trans_table);
-    }
-    else
-    {
-      /*
-        The engine does not support truncate-by-recreate. Open the
-        table and invoke the handler truncate. In such a manner this
-        can in fact open several tables if it's a temporary MyISAMMRG
-        table.
-      */
     error= handler_truncate(thd, table_ref, TRUE);
-    }
 
     /*
       No need to invalidate the query cache, queries with temporary

sql/unireg.cc

@@ -354,8 +354,7 @@ int rea_create_table(THD *thd, LEX_CUSTRING *frm,
 {
   DBUG_ENTER("rea_create_table");
 
-  // TODO don't write frm for temp tables
-  if (no_ha_create_table || create_info->tmp_table())
+  if (no_ha_create_table)
   {
     if (writefrm(path, db, table_name, true, frm->str, frm->length))
       goto err_frm;