Re: PQexecParams with binary resultFormat vs BINARY CURSOR

[Dmitriy Igrishin <dmitigr@xxxxxxxxx>]

2011/11/11 Mateusz Łoskot <mateusz@xxxxxxxxxx>

Hi Dmitriy,

2011/11/11 Dmitriy Igrishin <dmitigr@xxxxxxxxx>:

> 2011/11/11 Mateusz Łoskot <mateusz@xxxxxxxxxx>
>>
>> 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.