Re: TOAST (was: BLOB) - Mailing list pgsql-sql

Peter Eisentraut wrote:

> >     clob  is  a  user  defined,  very  simple varsize datatype, I
> >     created for testing.
>
> Keep it, it's SQL3.
   We don't need it later. At the time text is toastable, we can   simply create an alias for it and are done. And I
think blob   is bytea then, isn't it?
 

> >     Seems there's  something  wrong  in  our  deadlock  detection
> >     algorithm.
>
> Our deadlock detection "algorithm" is that when nothing happens for 1 sec
> then that's a deadlock. Increasing that number might make those messages
> go away but that's still far from an algorithm, of course.
   Really?  I  remember  that  someday it was "if I'm waiting 60   seconds for my lock, ...". What a change.
   What's the exact location of that parameter to change?

> >     I'll  need  alot  of  help  to  make  all  our existing types
> >     toastable,
>
> I'm wondering how transparent all of this will be. What is involved in
> making existing types toastable? How does that affect user defined
> datatypes now and in the future?
   Let's look at the input/output functions of clob:
   void *   clob_in(char *s)   {       void       *c;       int32       l;
       if (s == NULL)           return NULL;
       l = strlen(s);       c = (void *)palloc(VARHDRSZ + l);
       VARATT_SIZEP(c) = l + VARHDRSZ;       memcpy(VARATT_DATA(c), s, l);
       return c;   }

   char *   clob_out(void *c)   {       void       *p;       char       *s;       int32       l;
       if (c == NULL)       {           s = palloc(2);           s[0] = '-';           s[1] = '\0';           return s;
     }
 
       VARATT_GETPLAIN(c, p);
       l = VARATT_SIZE(p) - VARHDRSZ;       s = (char *)palloc(l + 1);       memcpy(s, VARATT_DATA(p), l);       s[l] =
'\0';
       VARATT_FREE(c, p);
       return s;   }
   So the input function doesn't change at all.  Only  functions   that  have  a  toastable type as argument need to
wraparound   with   a   local   variable   and   the    VARATT_GETPLAIN(),   VARATT_FREE() macros.
 
   VARATT_GETPLAIN(arg,  ptr)  places  the plain value of arg in   ptr.  If the argument wasn't toasted, it's assigned
asis. If   compressed   or   stored  external,  the  original  value  is   reconstructed in palloc()'d memory and
assignedto ptr.
 
   VARATT_FREE(arg, ptr) free()'s ptr if it  is  different  from   arg.
   It  all ain't that complicated. Easy enough to use it in user   defined types  too  (a  must  because  today's  user
defined   functions  usually  use  our base types too). Only that there   are hundreds of functions in utils/adt and
contribthat  need   to be looked at.
 


Jan

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