Getting SQL*Net more data from client waits when running a query through web based interface

Question

Hi, you all,
We are having this weird behavior when running query through web based interface, we get a lot of "SQL*Net more data from client" waits, the OEM indicates that the current wait event is SQL*Net more data from client
It's just a very simple query wich invokes a db link.
When I execute the same query on any PL/SQL tool like toad or sql developer it works fine, but that query inside an application executed through a web based interface, it hangs for ever.
Where can I start looking for the problem.
We are working on a 3 Node RAC 11gr2, both databases are on the same RAC.
Thanks.

Answer 1

Hi ,
we managed to reproduce the case in test environment, below are the steps:
1)have 2 databases on different machines, will call the first one local, the other one remote.
2)in the local database create:
a - DBLink to remote database.
b - read data from remote database(we simply used select count(*) from dummy_table )
c - insert data into a table on the local database
d - terminate the connection between the 2 databases (disconnect either machine from the network)
e - commit on local database.
what we noticed was the following:
1)when the local database is disconnected from the network(the machine is not connected to any network at the moment): almost immediately throws an error, and issuing the following:
select * from dba_2pc_pending;we found some data .
2) when the remote database was disconnected(the local database is still connected to the network):
after 7-8 seconds an error is thrown, and issuing the following:
select * from dba_2pc_pending;did not return any data.
since this is pretty similar to our case ,we concluded that it's a network issue.
is this the correct behavior ?
as a temporary solution till the network issue is fixed ,we did the following:
1) changed the call of the remote procedure to calling a local procedure that calls the remote procedure.
2) added pragma autonomous_transaction to the local procedure.
3) at the end of the local procedure rollback the autonomous transaction.
it seems that since the global transaction does not use the DBLink database does not issue a 2PC commit.
this works in my cases since the DBLink is only issed to read data.