Detecting backend failures via libpq / DBD::Pg

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I am working on enhancing the ping() method of DBD::Pg. The goal of that
is for a user to be able to determine if the connection to the database
is still valid. The basic way we do this is to send a simple SELECT via
PQexec and then check for a valid return value (and when in doubt, we check
PQstatus). This works fine for most transaction statuses, including idle,
active, and idle in transaction. It even works for copy in and copy out,
although it obviously invalidates the current COPY (caveat emptor!).
The problem comes when ping() is called and we are in a failed transaction.
After some experimenting, the best solution I found is to send the PQexec,
and then check if PQresultErrorField(result, 'C') is '25P02'. If it is, then
all is "well", in that the server is still alive. If it is not, then we
can assume the backend is bad (for example, PQerrorMessage gives a
"could not receive data from server: Bad file descriptor"). Being that we
cannot do a rollback before calling the PQexec, is this a decent solution?
Can we depend on really serious errors always trumping the expected 25P02?

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Greg Sabino Mullane greg(at)turnstep(dot)com
End Point Corporation http://www.endpoint.com/
PGP Key: 0x14964AC8 201412291942
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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