Re: problem connecting to db.
- From: Charles Hooper <hooperc2000@xxxxxxxxx>
- Date: Thu, 27 Dec 2007 09:11:49 -0800 (PST)
On Dec 27, 6:26 am, "Mr. X." <no_spam_please@xxxxxxxxxxxxxxxxx> wrote:
Hello,
In my VB 6.0 code, I have tried to connect to oracle-database,
but program just hang (even there is no exception !!!)
Code is :
In alert.log there is a massage (it sometimes occurs when the above hang,
but not always when the program hangs) :
SMON: Parallel transaction recovery tried
The code in brief:
--------------------
Public OraCon As New ADODB.Connection
Public mainConnectionStr As String
...
public sub connectToDB
On Error GoTo connectToDB_err
mainConnectionStr = ...
OraCon.ConnectionString = mainConnectionStr
Call OraCon.Open ' ***** here programs hang sometimes ******
' ***** also, when hang - not always there
is a line on alert.log, but sometimes there is. ******
goto end_proc
connectToDB_err:
' ****** when the above error, this code is never reachable *******
msgBox "" & err.number & "," & err.description
end_proc:
end sub
What may be the cause for the above problem ?
Thanks :)
Just a couple suggestions. Before the Call OraCon.Open line (note
that the word Call is unnecessary), add the following:
OraCon.ConnectionTimeout = 30
OraCon.CursorLocation = adUseClient
Have you checked the listener log file on the database server? The
log file may be very large, so you may either want to examine just the
tail of the log, or copy it to another computer for viewing. It is
possible that the computer is trying to find the database using DNS or
something similar. Make certain that the TNSNAMES.ORA file on the
client is correct, and that the connection string that you are
specifying in VB6 matches that in the TNSNAMES.ORA file. For example,
if the TNSNAMES.ORA on the client contains the following:
LT =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = AIRFORCE_1)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = MYDB1)
)
)
In this case, the VB6 connection string should specify LT, and not
MYDB1. In the above, the Oracle client would be looking for a server
named AIRFORCE_1. If the DNS server is down, the client would likely
experience at least a 30 second delay before the computer used another
method to resolve the IP address of the AIRFORCE_1 server - it might
be a good idea to see what would happen if you specify the server's IP
address in the TNSNAMES.ORA file on the client.
There is a Usenet posting from 2004 that implies that the error in the
alert log may be related to the initialization parameters used by the
Oracle instance:
http://groups.google.com/group/comp.databases.oracle.server/browse_thread/thread/86ca345ebfabc168
If possible, post the list of initialization parameters used by the
database instance.
If you do not have physical access to the server, I suggest running a
Wireshark/Ethereal trace on the client while attempting to connect to
the database. If you see a DNS lookup request, and then a 30+ second
pause, that likely means that the DNS server was unavailable to
resolve the database server name - check the status of the internal
DNS server. If you see a response from the DNS server, and then a
connection request to Oracle, but no response back from the server
hosting the Oracle database, then the problem is likely in/on the
Oracle server or the network segment between the server and the
client. A couple weeks ago I saw a similar problem, where the limit
set for processes in the initialization parameters was hit - in some
cases the clients would hang when attempting to connect to the
database, and in others the clients would be told that the connection
request failed. The listener log file showed that it could not hand
off the connection requests to the database instance.
Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc.
.
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