libpq - PQsendQuery wait for complete result

Question

I'm having problem with libpq's PQexec function hanging on intermittent connections. After looking around the mailing list, the solution is to use the asynchronous functions PQsendQuery/PQgetResult and implement your own timeout.

Now the issue I'm facing is that PQgetResult needs to be called multiple times until it returns null and then you know it's done. However, the rest of my application expects a single PQresult object per query.

So my question is:

1. Is there a way to concatenate/join the multiple PQresults?
2. Can I somehow use PQisBusy & PQconsumeInput to wait until all the results are ready before calling PQgetResult?

Answer 1

credits to Laurenz Albe to who answered this over on the postgresql mailing list.

If you have a single SQL statement, you will get only one PQresult. You get more than one if you send a query string with more than one statement, e.g.

PQsendQuery(conn, "SELECT 42; SELECT 'Hello'"); 

would result in two PQresults.

You can get multiple PQresults only using asynchronous command processing; the corresponding PQexec would return only the PQresult of the last statement executed.

So you can get the same behaviour as PQexec by discarding all PQresults except for the last one.