Обсуждение: Toast and slice of toast

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Toast and slice of toast

От
Rémi Cura
Дата:
Hey Dear List,
could somebody point me to some ressources about getting only parts of toasted data?

I have a very big custom type and I would like to take blocks of it (like byte A to B then byte C to D  then... ).

I found a function in http://doxygen.postgresql.org/tuptoaster_8c.html# called toast_fetch_datum_slice, is it the right way to use it
(a for loop and calling it several time?).

Thanks,

Cheers

Rémi-C

Re: Toast and slice of toast

От
Haribabu Kommi
Дата:
On Sun, Feb 16, 2014 at 9:38 PM, Rémi Cura <remi.cura@gmail.com> wrote:
Hey Dear List,
could somebody point me to some ressources about getting only parts of toasted data?

I have a very big custom type and I would like to take blocks of it (like byte A to B then byte C to D  then... ).

I found a function in http://doxygen.postgresql.org/tuptoaster_8c.html# called toast_fetch_datum_slice, is it the right way to use it
(a for loop and calling it several time?).

"pg_detoast_datum_slice" is the function which will solve your problem.
 
Regards,
Hari Babu
Fujitsu Australia

Re: Toast and slice of toast

От
Andres Freund
Дата:
On 2014-02-17 14:16:33 +1100, Haribabu Kommi wrote:
> On Sun, Feb 16, 2014 at 9:38 PM, Rémi Cura <remi.cura@gmail.com> wrote:
>
> > Hey Dear List,
> > could somebody point me to some ressources about getting only parts of
> > toasted data?
> >
> > I have a very big custom type and I would like to take blocks of it (like
> > byte A to B then byte C to D  then... ).
> >
> > I found a function in http://doxygen.postgresql.org/tuptoaster_8c.html#called toast_fetch_datum_slice, is it the
rightway to use it 
> > (a for loop and calling it several time?).
> >
>
> "pg_detoast_datum_slice" is the function which will solve your problem.

Note that you need to prevent your type/column from being compressed for
that being effective. Check the storage options for CREATE TABLE et al.

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Re: Toast and slice of toast

От
Rémi Cura
Дата:
Thanks everybody !

Cheers,

Rémi-C


2014-02-17 10:37 GMT+01:00 Andres Freund <andres@2ndquadrant.com>:
On 2014-02-17 14:16:33 +1100, Haribabu Kommi wrote:
> On Sun, Feb 16, 2014 at 9:38 PM, Rémi Cura <remi.cura@gmail.com> wrote:
>
> > Hey Dear List,
> > could somebody point me to some ressources about getting only parts of
> > toasted data?
> >
> > I have a very big custom type and I would like to take blocks of it (like
> > byte A to B then byte C to D  then... ).
> >
> > I found a function in http://doxygen.postgresql.org/tuptoaster_8c.html#called toast_fetch_datum_slice, is it the right way to use it
> > (a for loop and calling it several time?).
> >
>
> "pg_detoast_datum_slice" is the function which will solve your problem.

Note that you need to prevent your type/column from being compressed for
that being effective. Check the storage options for CREATE TABLE et al.

Greetings,

Andres Freund

--
 Andres Freund                     http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services