Message-ID: <53F379CF.5090100@vmware.com>
Date: Tue, 19 Aug 2014 19:22:39 +0300
From: Heikki Linnakangas <hlinnakangas@vmware.com>
Organization: VMware
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To: Alvaro Herrera <alvherre@2ndquadrant.com>, Stephen Frost
 <sfrost@snowman.net>
CC: PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: PQgetssl() and alternative SSL implementations
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 <20140819154436.GD16422@tamriel.snowman.net>
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On 08/19/2014 07:10 PM, Alvaro Herrera wrote:
> Stephen Frost wrote:
>> * Heikki Linnakangas (hlinnakangas@vmware.com) wrote:
>>
>>> Indeed, the ODBC driver only uses libpq for authentication, then
>>> calls PQgetssl(), and takes over the whole show calling SSL_read()
>>> and SSL_write() itself. Ideally, we'd modify psqlodbc to stop doing
>>> that, but that's not an easy job. In the short-term, I think we need
>>> to export pqsecure_read() and pqsecure_write() functions in libpq,
>>> so that the ODBC driver can use those instead of SSL_read() and
>>> SSL_write().
>>
>> Yeah, that's what I remembered.  There was an attempt to make that
>> change at one point, but it was reverted due to the lack of batching
>> ability in libpq (without resorting to cursors, as I recall...),
>> requiring double the memory usage.  Still, if pqsecure_read and
>> pqsecure_write are sufficient to make the ODBC driver work, that's good
>> news.  I had been worried it did other things with the OpenSSL struct
>> beyond just using those.
>
> Um, libpq has recently gained the ability to return result fragments,
> right?  Those didn't exist when libpq-ification of odbc was attempted,
> as I recall -- perhaps it's possible now.

IIRC the thing that psqlodbc does that libpq doesn't support is sending 
multiple queries to the backend, and then wait for *all* the replies to 
arrive, in a single round-trip. The closest thing is using PQexec("foo; 
bar;"), but that's quite limited.

- Heikki


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