[kepler-users] Database Connection and Database Query

[Frank Steinmann]

Hi,

I am using Database Queries in several parts of a complex workflow (i.e. 
in different composite actors). Because the queries are all sent to the 
same database, I am creating a single database connection and send it to 
all actors needing it. Some of the composite actors which have a 
Database Query inside need to be fired several times, therefore I am 
using the repeat actor to send the database connection token several times.

But the Database Query actor only takes the first token and once it has 
a database connection it does not read tokens from the dbcon port 
anymore. Looking deeply into the bowels of the SDF kernel I found out 
that each port has a queue and the capacity of this queue may be finite 
or infinite, where infinite capacity is the default. For some reason the 
capacity of the dbcon port of the Database Query actor is set to one 
(strangely, this happens only the first time I run the workflow after 
opening it, in every following run it is not set explicitely and 
therefore infinite).
Now what happens should be clear: When the composite actor (containing 
the Database Query) is fired the first time, the db connection token is 
send to and taken by the Database Query. When fired the second time, 
again a db connection token is send to the Database Query but it is not 
taken. When fired the third time, another db connection token shall be 
sent to the Database Query, but as the queue capacity is one and there 
is already the token from the last iteration in the queue, the token 
cannot be sent, which leads to an exception.

How should I handle this correctly? I think in a clean solution the 
connection token would be sent only once. But I get an exception when 
trying to fire the composite actor without having sent a token to the db 
connection port.
Is there a way to fire a composite actor without having tokens at all 
input ports (in SDF or DDF domain)?
If not, is there a way to set the capacity of the queue of the dbcon 
port to infitity (I would not like this solution, but with infinite 
queue capacity it would at least work).
Is there a totally different solution?

Thanks in advance,
Frank


-- 
Dipl.-Inf. Frank Steinmann
Knowledge Management Department
DFKI GmbH

Tel.:    +49 (0)631 20575 - 114
Sekr.:   +49 (0)631 20575 - 101
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E-Mail: Frank.Steinmann at dfki.de
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