Re: funny (cache (?)) bug in postgres (7.x tested)

On Thu, 28 Jun 2001, RISKO Gergely wrote:

> text *hupper (text *a) {
>     int hossz,i;
> 
>     hossz=a->vl_len;
>     for (i=0;i<hossz;i++)
>     {
>         char ch;
>         ch=a->vl_dat[i];
>         if ((ch>=97)&(ch<=122)) ch=ch-32;
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         else if (ch=='�') ch='�';
>         a->vl_dat[i]=ch;
>     }
> 
>     return a;
> }
(Rest snipped).

You are not supposed to write directly to the argument you are given. You
must construct a new text value (by allocating space via palloc) and
copy your string there. By overwriting existing values, you potentially
corrupt postgres' cache, resulting in your behaviour.