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MySql - Lost Connection to mySql during query

Posted on 2009-05-06
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Last Modified: 2013-11-07
Hi,

I am supporting an application written in VB.net with MySql 5.0 as a backend
Recently  the application started to give error messages stating "Lost Connection to MySQL server during query"

This error can popup every then and now during any query, regardless of the  anything - just random....

I have changed timeouts, packetsizes - In short tried any suggestions that I could find on the MySql web site and other web resources

I have strong feeling that this is networking issue but I have no experience in troubleshooting such issues so I am lost at this point and need your help.

Any suggestions on what could be done?
Please note that this is production database and I am very limited in what I can do with it (at least I will need some good reasons to restart mySql or such things)

Please help!!!
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Question by:Michael_D
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Expert Comment

by:louislietaer
ID: 24317578
How long is your query ?
What the select command look like?


As your database is in production, you could install one mysql server on your pc very easily to make tour test. a dump and restore will be enough to restore data on your pc and the to run your tests without any streess ;)
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Expert Comment

by:oobayly
ID: 24318403
I find Wireshark invaluable for troubleshooting Network issues, especially for apps that maintain an open connection to a server. Monitor any traffic on port 3306, look for large amounts of retransmissions or RST packets.

http://www.wireshark.org/
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Author Comment

by:Michael_D
ID: 24318497
The problem is that it could be ANY query.
users get sometime this error when providing username and password to login to system.
select command looks like Select * from employee where empCode='bla-bla'
employee table have about 200 records with index on empCode

Also I noticed that this error most probably will appear after long idle time.
I am getting this errors even when I am working with database tools like Toad for MySql or SQLyog
let say I run a query that returns a result almost immediately. then I do something else for couple of minutes and refresh my query sometime the error to show up - there is no way to reproduce this - it just happens randomly. I realize that nothing can happen just "randomly" that why I am looking for a way to find what causing this.

As the production server - we do have another server for testing and development but the error never happens when I am connecting to that one - just on production server.
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Author Comment

by:Michael_D
ID: 24318751
>>> oobayly

Can you tell me how to configure the Wireshark so i can use the captured info? I am a software developer not a network administrator and have very limited knowledge of networks protocols. And my client is small family business and he cannot afford to hire a network professional to investigate this issue. But he paid for software and expect it work so it is kind of my responsibility to find and eliminate any issues...
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Accepted Solution

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oobayly earned 500 total points
ID: 24319379
Is the server on a remote site?

As for using WireShark, for a simple capture, just select "Options" from the "Capture" menu.
Select the correct Network Card
Enter "tcp port 3306" in the "Capture Filter" textbox.

Keep the capture going, and have a look at anything abnormal, when you get a lost connection. Abnormal would be repeated retransmissions, resets while a data is being recived.

Optionally, you can also set a display filter to show all the mysql commands by entering "mysql" in the Filter textbox on the toolbar while a capture is running. This will filter out any of the TCP entries, but will make it less clear when an error occurs.
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Author Comment

by:Michael_D
ID: 24355657
I have increased wait_timeout and seems like the amount of the lost connections decreased.

I am going to accept oobayly's suggestion to use WireShark as a tool to troubleshoot the issue. At least I have found that there is no abnormal packages traveling through network
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Author Closing Comment

by:Michael_D
ID: 31578549
Thank you!
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