2011/11/11 Mateusz Łoskot <mate...@loskot.net> > Hi Dmitriy, > > 2011/11/11 Dmitriy Igrishin <dmit...@gmail.com>: > > 2011/11/11 Mateusz Łoskot <mate...@loskot.net> > >> > >> Considering query for binary data stored directly in tables > >> using libpq API, I'm trying to understand what is the difference > >> between specifying binary format in functions like > >> PQexecParams and use of BINARY CURSOR. > >> > >> For example, with query like this: > >> > >> SELECT large_image FROM tbl; > >> > >> where large_image is a custom type, > >> is there a big difference between binary format specified > >> to libpq and use of BINARY CURSOR? > >> Is it client-side binary vs server-side binary processing? > >> > >> Simply, I'd like to avoid textual<->binary conversions at any stage. > >> > >> (Endianness is not an issue here.) > >> > >> Best regards, > > > > "...The concept of a binary cursor as such is thus obsolete when using > > extended query protocol — any cursor can be treated as either text or > > binary. ..." from > > http://www.postgresql.org/docs/9.1/static/sql-declare.html > > Thanks, this is interesting. > I've been reading more about this and the picture seems to be clear: > > "Note: The choice between text and binary output is determined by the > format > codes given in Bind, regardless of the SQL command involved." > > > http://www.postgresql.org/docs/9.1/static/protocol-flow.html#PROTOCOL-FLOW-EXT-QUERY > > However, I'm not sure how I can utilise this feature of the extended > query protocol > with libpq API. Concretely, how to translate the binding with format > specification here > > "choice between text and binary output is determined by the format > codes given in Bind" > > Does it mean the protocol automagically switches between text/binary > depending on > format code (0|1) specified to PQexecParams and friends? > The Bind(F) message contains array with the parameter format codes. So, yes, all you need is to pass array with format codes to ::PQexecParams and libpq will let it go.
> > Side question, is this new feature of the extended query protocol in 9.x > line? > The "extended query" sub-protocol introduced in protocol version 3.0. -- // Dmitriy.
