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Re: Review request for a fix for MDEV-5506


Hi, Alexander!

On Jan 27, Alexander Barkov wrote:
> On 01/26/2014 11:23 PM, Sergei Golubchik wrote:
> >
> > Okay, I understand what you did. But I don't understand why.
> > What was the problem? Why there was a crash?
> - Item_func_make_set::val_str() returns &my_empty_string
> After the fix my_empty_string:
> - remembers that it is null terminated and does not call realloc() from
>    c_ptr_safe()
> - remembers that it is read-only and protects itself from realloc() by

I'd rather fix Item_func_make_set instead. Now it seems to be the only
Item that uses it (there's also SELECT ... OUTFILE, but that's

And Item_func_make_set has String tmp_str property, which is already
used as an internal storage.

So, I'd remove my_empty_string usage from Item_func_make_set whatsoever.
Simply with

-   String *result=&my_empty_string;
+   String *result=&tmp_str;
+   tmp_str.length(0);

In fact, perhaps Item_func_make_set::tmp_str is not needed at all, and
Item:str_value can be used instead:

-   String *result=&my_empty_string;
+   String *result=make_empty_result();


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