Re: invalid message format and I/O error while comunicating with backend

Yes, your are right

It is a problem related with multiple threads working on the same Prepared Statement.

I have modified the code to run with one single thread and it runs very smoothly.

Previously there were more than one thread working onthe same prepared statements (they were created at server startup) Even if the code already included some synchronization code, it seems I was loosing control of the threads.

I will modify the code, and make sure every thread has his own Prepared Statements.

I thought that sharing the same prepared statements was more efficient.

Thanks

Kris Jurka escribió:

This appears to be a thread safety related problem. I believe your code has one thread setting the parameter values and another thread executing the prepared statement at the same time. The executor does two passes through the parameter list, once to calculate a total message length and another time to send the values. If the contents change between the length calculation and the message sending we'll have the wrong length and the whole client-server communication gets messed up. The attached test case demonstrates this failure mode.

I'm unsure how hard we should try to fix this, there are a couple of approaches:

1) Do nothing. It's really a client problem and they shouldn't be setting and executing at the same time.

2) Just copy the parameters at execution time so we get a consistent view of them. This may not be exactly what the user wants though if the order things actually execute is: execute, set, copy instead of execute, copy, set.

3) Go through all the PreparedStatement functions making most of them synchronized so that you cannot set while an execute is running.

Kris Jurka

Sergi Vera wrote:

Hi!

I've been a little busy thoose days and was unable to work on this, but I've made the tcpdump session that you requested and

here are the results

Kris Jurka escribió:

Sergi Vera wrote:

Thanks Kris for the help

Adding loglevel=2 dind't add any more info on logs, and it will be not easy to make a self contained program, but I have attached the result of

The loglevel=2 logging will go to the driver's System.out not into the server error log.

tcpdump -vvv -i lo -w pgsqlerror2.dat

This only captures the start of each packet so it doesn't have the whole thing. Could you recapture with:

tcpdump -n -w pgsqlerror3.dat -s 1514 -i any tcp port 5432

This ups the capture size (-s 1514) and also filters out the unrelated UDP traffic you've got going on.

Browsing through the first failing pgsql data chunk, one can see that:

http://img139.imageshack.us/my.php?image=pantallazolm8.png

The last data has column lenght -1 which seems strange even if I don'k know anything of this particular protocol

-1 length indicates a NULL value, so that's expected.

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Sergio Vera

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