Michael Van Canneyt wrote:
On Mon, 28 Sep 2015, Mark Morgan Lloyd wrote:
Michael Van Canneyt wrote:
On Fri, 11 Sep 2015, Mark Morgan Lloyd wrote:
PostgreSQL has a useful feature where application programs can send
notifications to each other, this tends to be much "cheaper" than
periodically polling a table for changes.
I've had this working on various CPUs and OSes in a number of
programs since at least 2.2.4, but it appears to have been broken at
some point between 2.6.0 and 2.6.4 with problems persisting through
to 3.0.0-rc1 and trunk. The specific fragment of code that's failing
looks like this:
result := badPoll;
if PQStatus(DbTF.PQConnection1.Handle) <> CONNECTION_OK then
exit;
pqConsumeResult := PQconsumeInput(DbTF.PQConnection1.Handle);
if PQStatus(DbTF.PQConnection1.Handle) <> CONNECTION_OK then
exit;
If DbTF.PQConnection1 is of type TPQConnection then I think this is
your problem. The low-level handle has been moved to the transaction.
DbTF.PQConnection1.Handle is then a stub, of no value.
Any chance of a hint where to find the new long-life handle, i.e. the
one that corresponds to the connect action with username, password
etc. properties?
pqconnection, start of the unit:
{ TPQTrans }
TPQTrans = Class(TSQLHandle)
protected
PGConn : PPGConn;
FList : TThreadList;
Procedure RegisterCursor(Cursor : TPQCursor);
Procedure UnRegisterCursor(Cursor : TPQCursor);
Public
Constructor Create;
Destructor Destroy; override;
end;
PGConn is what you're looking for.
TPQTrans is referenced in :
TPQCursor = Class(TSQLCursor)
protected
Statement : string;
StmtName : string;
tr : TPQTrans;
Thanks, I'll take another look but one of the handles I'm tracking is
that PGConn field.
I can see handles changing state in debug output from both
lazarus-1.0.0+2.6.0 and lazarus-1.0.14+2.6.4 (intermediate versions e.g.
lazarus-1.0.8+2.6.2 are more of a problem), and can see them behaving
differently. Knowing that there isn't a third one that I've not yet
located is a big help.
The change was between 2.6.2 and 2.6.4, I've been looking at sqldb.pp
and related files but so far haven't tracked it down.
Discussing this sort of thing elsewhere, at least PostgreSQL,
Firebird/Interbase and Oracle provide comparable notification/event
features with varying degrees of functionality. If encapsulating this
sort of thing in libraries or components, it would be highly desirable
to be able to rely on the availability of a persistent handle.
The above should be sufficient ?
But the mechanisms are different for each DB, so a unified mechanism is
not something we are considering, to my knowledge.
If you look at the pqeventmonitor unit, you will see that it bypasses
completely the usual TSQLConnection mechanisms.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
