Hello,

I'm trying to devise a strategy for when the connection to the server fails. I'm using zeos but I also tried with sqldb and I couldn't find a way. I open a connection to the server, then I stop the server and subsequent operations (e.g. refreshing a query) fail (obviously since the connection has been severed).
However, for the same reason, I cannot close the connection (with sqldb by setting PQConnection.connected:=false or with zeos by calling ZConnection.Disconnect), since it raises an exception :-( With zeos I tried to get hold of the underlying handle and call PQReset before closing the connection.
The PQreset works, but the connection cannot be closed because it tries to release prepared statements that don't exist in the new connection so postgresql returns an error.....

Is there a way to force the closing of a connection in this case so I can try and reopen it again?

TIA

Try using forcedclose in SQLDb:

TheDatabase.Close(True);

Michael.

El 15/05/18 a les 20:44, Michael Van Canneyt ha escrit:

Project project1 raised exception class 'EPQDatabaseError' with message: PQConnection1: connection pointer is NULL
(PostgreSQL:)

In file 'fcl-db/src/sqldb/postgres/pqconnection.pp' ad line 725:
raise E;

TDatabase.DoDisconnect calls CloseDatasets which in turn calls Unprepare (in TCustomSQLQuery.SetActive)->
FStatement.Unprepare->
DoUnprepare->
Database.UnPrepareStatement(FCursor)->
TPQConnection.UnprepareStatement which eventually fails.

Bye

I will need to check this, but the purpose of Close(True) is exactly to ignore errors while closing for a reconnect.
It was introduced and tested in the case of MySQL, but normally should work on any database.

Can you please post a small sample program in the bugtracker ?

Michael.

El 15/05/18 a les 21:11, Michael Van Canneyt via Lazarus ha escrit:

Done

https://bugs.freepascal.org/view.php?id=33737

Thank you

El 15/05/18 a les 21:43, Luca Olivetti via Lazarus ha escrit:

Using the same project as in the bug report, almost every time I set the "Active" property of the SQLQuery1 component to true in the object inspector I get an "Access violation" and the selection tree in the object inspector gets messed up.
It doesn't happen if I use zeos.
I tried both with the original fcl-db and the one modified as my last message in the bug report (I rebuild lazarus every time I changed fcl-db). Fpc 3.0.4/lazarus 1.8.2, win32 and linux (64 bits)/qt

The access violation happens inside
TComponentTreeView.UpdateComponentsNodesValues, UpdateComponentNode, line "if APersistent is TComponent", when Anode is the first TSQLDBFieldDef in the sqlquery

Bye

El 17/5/18 a les 9:50, Luca Olivetti via Lazarus ha escrit:

I added a couple of comments to that bug (that I cannot reopen).

Bye

I reopened it. If you can implement a patch that checks forcedClosed for postgres, I will be glad to check & apply it...

Michael.

El 24/8/22 a les 12:50, Michael Van Canneyt ha escrit:

As you can see from the bug report, I tried, I failed, I gave up :-( I'll use the nuclear option that I used 4 years ago, i.e. brutally close the app if the connection to the database is severed, then a watchdog app will restart it.
In this case the client app and the postgresql server will run in the same pc so it shouldn't be a big issue (crossing fingers).

Bye

El 24/8/22 a les 13:15, Luca Olivetti via lazarus ha escrit:

Wait, it seems it's a simple fix. I'll attach a patch later if I see it works.

Bye