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Symptom:
When trying to do “edit table” or “query data” (as below) in pl/sql developer or try to run any SQL statement, the program will hang. Although schema browse works and connection to database server can be made withouth issue.

Trouble shooting:
I updated Oracle client to 11.2.0.3, upgrade pl/sql developer to the lasted version 9.0.6, no help.  I fired up TCPView (from www.sysinternals.com) and found there were 2 connections to server:


While on server side, we only got one:

I did a few more test, and turned out, sometimes, the first connection you made to the database may disappear on server side, when that happens, plsqldeveloper will hang.   So I traced server side Oracle process using “strace” as below (the number after –p is process ID as in above picture 32641/oracle….)
strace –p 32641
and in the trace file, I got:
write(20, "\2\274\0\0\6\0\0\0\0\0ssed\25\1\0\1\7 EHCC Query H"..., 700) = -1 ECONNRESET (Connection reset by peer)

that means the connection was reset, and that is mostly a software bug to me. To confirm the network reset was sent by plsqldeveoper, I downloaded wireshark (http://www.wireshark.org/) and did a client network capture, but there’s no reset packet was sent from client side. So I have to suspect the problem was on the network.
On my PC, I only got one network card (NIC) which is from Intel, but since sometimes I need to use VPN (Cisco VPN) to connect to production server, the VPN is always on. I disconnected VPN and try the same operation again, now everything works just as expected.
I did some other test using other tools like sqlplus and sqldeveloper, both works without issue on Cisco VPN.
Root cause:
There’s something wrong when use plsqldevelop and Cisco VPN together or maybe there’s some settings on VPN side caused the problem. Anyway I this case, I need to disable VPN to make plsql developer work.

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