Thread: DETOAST Datum

Hi,<br />I have defined some function and also used NDBOX structure that having variable length.<br /><br />typedef
structNDBOX<br />{<br />    int32        vl_len_;        /* varlena length */<br />    unsigned int dim;<br />   
double       x[1];<br /> } NDBOX;<br /><br />When i called my function, it gives NDBOX to be null<br />On debugging, i
foundout ,FunctionInvokeCall invokes fmgr_oldstyle function, for getting argument<br /><br />if
(fnextra->arg_toastable[i])   //this returns false, not able to get arguments<br />             fcinfo->arg[i] =
PointerGetDatum(PG_DETOAST_DATUM(fcinfo->arg[i]));<br/>    } <br /><br />"How to get arguments toastable??" and even
mytable pg_class.reltoastrelid entry is zero.<br />Can i have to tell explicitly to toast?<br /><br />If i commented
thatif conditions then, it got stuck below:<br /><br />struct varlena *<br />pg_detoast_datum(struct varlena *
datum)<br/>{<br />    if (VARATT_IS_EXTENDED(datum))      //My code get stuck here<br />        return
heap_tuple_untoast_attr(datum);<br/>     else<br />        return datum;<br />}<br /><br />Can anyone tell me what
VARATT_IS_EXTENDED(datum)mean?<br /><br />Thanks<br /> 

On Mon, May 16, 2011 at 3:41 AM, Nick Raj <nickrajjain@gmail.com> wrote:
> When i called my function, it gives NDBOX to be null
> On debugging, i found out ,FunctionInvokeCall invokes fmgr_oldstyle
> function, for getting argument
>
> if (fnextra->arg_toastable[i])    //this returns false, not able to get
> arguments
>             fcinfo->arg[i] =
> PointerGetDatum(PG_DETOAST_DATUM(fcinfo->arg[i]));
>     }
>
> "How to get arguments toastable??" and even my table pg_class.reltoastrelid
> entry is zero.

It's pretty hard to guess what's going wrong here from the information
you've provided.  But reltoastid should not be 0 if you're using a
variable-length data type.  It's not exactly clear what you've done
wrong though.  Are you sure that the type is defined properly, as a
variable-length type?

> Can i have to tell explicitly to toast?

No, you don't have to tell it that.

> If i commented that if conditions then, it got stuck below:
>
> struct varlena *
> pg_detoast_datum(struct varlena * datum)
> {
>     if (VARATT_IS_EXTENDED(datum))      //My code get stuck here
>         return heap_tuple_untoast_attr(datum);
>     else
>         return datum;
> }
>
> Can anyone tell me what VARATT_IS_EXTENDED(datum) mean?

VARATT_IS_EXTENDED() returns true for datums that can be detoasted,
because they are (1) they are stored out-of-line in the TOAST table,
(2) compressed, or (3) unaligned, using a 1-byte header.  See
src/include/postgres.h.  But I seriously doubt that you need to debug
pg_detoast_datum().  If you're getting a failure there, it's because
something wasn't done right much earlier on in the process.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, May 16, 2011 at 3:41 AM, Nick Raj <nickrajjain@gmail.com> wrote:
>> "How to get arguments toastable??" and even my table pg_class.reltoastrelid
>> entry is zero.

> It's pretty hard to guess what's going wrong here from the information
> you've provided.  But reltoastid should not be 0 if you're using a
> variable-length data type.

It could be if the type is not marked toastable (ie, has storage class
PLAIN, which I think is the default even for varlena types).

But in any case I suspect that 90% of the problem here is an incorrect
declaration of the *function* not the type.  We haven't seen the C
function declaration, nor the SQL CREATE FUNCTION command, but if it's
going through fmgr_oldstyle then there isn't a PG_FUNCTION_INFO_V1
marker, which maybe is the problem.
        regards, tom lane