Simon Riggs <simon@2ndquadrant.com> writes: > On 11 June 2015 at 22:12, Shay Rojansky <roji@roji.org> wrote: >> Just in case it's interesting to you... The reason we implemented things >> this way is in order to avoid a deadlock situation - if we send two queries >> as P1/D1/B1/E1/P2/D2/B2/E2, and the first query has a large resultset, >> PostgreSQL may block writing the resultset, since Npgsql isn't reading it >> at that point. Npgsql on its part may get stuck writing the second query >> (if it's big enough) since PostgreSQL isn't reading on its end (thanks to >> Emil Lenngren for pointing this out originally).
> That part does sound like a problem that we have no good answer to. Sounds > worth starting a new thread on that.
I do not accept that the backend needs to deal with that; it's the responsibility of the client side to manage buffering properly if it is trying to overlap sending the next query with receipt of data from a previous one. See commit 2a3f6e368 for a related issue in libpq.
Then it's our responsibility to define what "manage buffering properly" means and document it.
People should be able to talk to us without risk of deadlock.
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
