wow, it was right under my nose. Thank you very much ! Cheers, Remi-C Le mar. 13 nov. 2018 à 19:00, Tom Lane <t...@sss.pgh.pa.us> a écrit :
> =?UTF-8?Q?R=C3=A9mi_Cura?= <remi.c...@gmail.com> writes: > > So the pgpointcloud store sometimes very large groups of points into one > > row (TOASTED), something along few kB to few MB. TOAST would be in > EXTERNAL > > mode (no compression). > > Sometimes we only want to access a part of this data (one or several > blocks > > within the full data). > >> From what I understand, for the moment it requires to fetch all the > data > > from disk, then de-toast it, then select only the part of the data we are > > interested in. > > > Yet I think it is possible to detoast only a subset of the data (and thus > > fetch only some part of the data), considering that the [doc on toast]( > > https://www.postgresql.org/docs/11/storage-toast.html) says > >> " Use of EXTERNAL will make substring operations on wide text and bytea > > columns faster > >> (at the penalty of increased storage space) because these operations are > > optimized > >> to fetch only the required parts of the out-of-line value when it is not > > compressed. " > > > So my question is how does it work, how easy would it be to implement for > > pgpointcloud? > > See PG_DETOAST_DATUM_SLICE and users of that macro. > > regards, tom lane >
