Commit ba7d8ad7 authored by unknown's avatar unknown

Improve a comment.

parent 908ff34e
......@@ -1162,12 +1162,22 @@ public:
This is to track items changed during execution of a prepared
statement/stored procedure. It's created by
register_item_tree_change() in memory root of THD, and freed in
rollback_item_tree_changes(). For conventional execution it's always 0.
rollback_item_tree_changes(). For conventional execution it's always
empty.
*/
Item_change_list change_list;
/*
Current prepared Query_arena if there one, or 0
A permanent memory area of the statement. For conventional
execution, the parsed tree and execution runtime reside in the same
memory root. In this case current_arena points to THD. In case of
a prepared statement or a stored procedure statement, thd->mem_root
conventionally points to runtime memory, and thd->current_arena
points to the memory of the PS/SP, where the parsed tree of the
statement resides. Whenever you need to perform a permanent
transformation of a parsed tree, you should allocate new memory in
current_arena, to allow correct re-execution of PS/SP.
Note: in the parser, current_arena == thd, even for PS/SP.
*/
Query_arena *current_arena;
/*
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment