I run a java programm and try to use it with a hosted DB, I run the Vserver ubuntu 12.04 with Mysql myself, full root-access.
I changed the my.cnf to have more resources.
When I start the application it is fast, hardly any difference to a local database.
My problem is that after a while of inactivity the program freezes probably because the connection dropped.
There is no entry in any errorlog. If I kill the application and restart it, it is working again, nothing else but kill works, it is a linuxPC.
I used ?autoReconnect=true but I am not sure this is correct, the tables are innodb.
Does anyone have an idea how to avoid the connection to drop or how to make sure a reconnection is made?
PS [17.12.2015]
?autoReconnect=true was removed
today I got some details after a long wait
com.openbravo.basic.BasicException:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 2.435.471 milliseconds ago. The last packet sent successfully to the server was 959.832 milliseconds ago.
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException:
Communications link failure
The last packet successfully received from the server was 2.435.471 milliseconds ago. The last packet sent successfully to the server was 959.832 milliseconds ago.
java.net.SocketException:
Is this what happens when wait_timeout is too short?
After the "error" the program worked again!
Your question lacks specific info, but I guess what is happen. MySQL Server has a parameter called wait_timeout (See official doc).
When you have a connection that exceed that timeout, MySQL will close it, and if you don't manage SQLExceptions properly, your application will have problems.
You can try to increase wait_timeout or review your connection code to manage exceptions, but both are workarounds.
I wouldn't recommend you to relay on autoReconnect as an alternative for any problem, instead it would be better to encapsulate connection management into business logic in order to manage open/close connection every time you need. Maybe connection pooling can help you.
I mean, when you call a business method from you UI (it doesn't mind if it is web, ws, desktop or whatever) you have to manage open connection and start transaction, (and other cross cutting concerns as authorization, audit, log, ...). During all businesses logic, control possible exceptions, commit or rollback and free resources.
If you post some code, you will get more specific answers.
Hope it helps!
autoReconnect is dangerous for InnoDB. When the connection is lost in the middle of a transaction the previous actions in the transaction are rolled back. But the code proceeds to run as if the transaction continues. This can lead to subsequent writes not being consistent with the rolled back data.
You would be better off recognizing the lost connection and restarting the transaction.
I know this sort of question has been asked for a few times, I read some of them but did not get any smarter.
My Java application is connecting to a database server via JDBC through a SSH Tunnel. The tunnel is opened once at beginning. When starting I opened the database connection everytime it is used. Due to changes in the app I needed the connection opened on startup and decided to keep it open until my application is closed. When I close the app I sometimes, not always, get following error:
- Could not retrieve transation read-only status server
java.sql.SQLException: Could not retrieve transation read-only status server
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 369.901 milliseconds ago. The last packet sent successfully to the server was 8 milliseconds ago.
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
Could this be because of the always open database connection? I test the application only for short times. It will run on 4 computers all day long. Can I expect this error more often then? The connection is used every few minutes, so it should be more performant to keep it open, but maybe during break it is not used for half an hour.
What would you recommend me to do? Always reopen the connection or keep it like it is and find a workaround when I get this error? Do you maybe have another idea why this error appears?
Just ask if you need more error log, database code or whatever you need.
Thanks!
I'm going to say yes, your issue is probably due to the fact that you have a persistent connection open.
I took over a website a while ago and the guy before me had the same idea: Open a single connection, send the queries through it when needed, and never close it. A month after I took over the site, the database wouldn't return any more query results just like this.
As a general rule of thumb and for good programming practice, always clean up after yourself. If you're not using a variable, set it to null and delete it. Not using a connection? Terminate it. This is way less prominent in Java than it is in C++ as Java does all the cleaning up for you for the most part.
I am trying to insert the tens of millions of data into oracle database by through java application but after 850k data inserted I am getting the error:
java.sql.exception: IO Exception :Connection reset by peer socket
write error.
I have a similar issue in my aplication.
In my case, after a few minutes in which the connection has not used, oracle server resets the connection and when I had to use it again, this exception was thrown.
I found that the problem was that oracle sets the timeout for connection at 10 minutes in sqlora.net file.
Maybe you can try to increase this time interval or check if the connection is still valid instead to check if it is closed (a connection can be not valid even if it is not closed).
The last option works fine for me.
I hope this helps.
I am having a strange issue with an exisitng servlet based applications (a litte old one).
I cannot get any servlets to complete operation, if it has a mysql prepared statement running slower than 10 seconds (I only have prepared statements in this app).
I dont have a problem with faster queries (less than 10 second).
catelina.out does not have any trace nor the browser interface. When I inspect the browser request through fiddler it shows
"This session is not yet complete. Press F5 to refresh when session is
complete for updated statistics. Request Count: 1 Bytes Sent:
437 (headers:437; body:0) Bytes Received: 0 (headers:0; body:0)"
MySQL "SHOW FULL PROCESSLIST" command shows the prticular socket connection (of a slow query) running for about 12 seconds with COMMAND="Execute" and STATE="Sending Data", then changing to COMMAND="Sleep" and STATE="" and stays like this for a long time (more than 500 seconds).
Ideally this connection should not remain as a SLEEP for such a long time, but close after completion of sending data.
netstat -ab command shows the same connection as ESTABLISHED under tomcat6.exe and mysqld.exe.
Ideally this should stay as TIME_WAIT once the query execution is finished till the "TcpTimedWaitDelay" value.
Expected payload of this query is pretty nominal (around 2kbytes).
MySQL connect_timeout=100 and Tomcat connectionTimeout="100000" (for the port 8000 which I am running the app).
One thing I did not try to change is the JDBC DriverManager.setLoginTimeout property, since it is only concerned until getting the connection.
This app was working quite well until a couple of days back. but I do not have any statistics with me on the query execution time during those days.
I am running windows 2008 R2 std edition, tomcat 6 and MySQL 5.5.
I cannot pinpoint this behaviour to any cause. appreciate your help very much.
It seems to be an issue related to the MySQL connector. We were using the old connector (version 3.1.x) . Latest stable version(5.1.20) fixed the issue.
This question already has answers here:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
(51 answers)
Closed 6 years ago.
My program that connects to a MySQL database was working fine. Then, without changing any code used to set up the connection, I get this exception:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
What happened?
The code used to get the connection:
private static Connection getDBConnection() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
String username = "user";
String password = "pass";
String url = "jdbc:mysql://www.domain.com:3306/dbName?connectTimeout=3000";
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection(url, username, password);
return conn;
}
This is a wrapped exception and not really interesting. It is the root cause of the exception which actually tells us something about the root cause. Please look a bit further in the stacktrace. The chance is big that you'll then face a SQLException: Connection refused or SQLException: Connection timed out.
If this is true in your case as well, then all the possible causes are:
IP address or hostname in JDBC URL is wrong.
Hostname in JDBC URL is not recognized by local DNS server.
Port number is missing or wrong in JDBC URL.
DB server is down.
DB server doesn't accept TCP/IP connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
To solve the one or the either, follow the following advices:
Verify and test them with ping.
Refresh DNS or use IP address in JDBC URL instead.
Verify it based on my.cnf of MySQL DB.
Start it.
Verify if mysqld is started without the --skip-networking option.
Disable firewall and/or configure firewall/proxy to allow/forward the port.
By the way (and unrelated to the actual problem), you don't necessarily need to load the JDBC driver on every getConnection() call. Just only once during startup is enough.
check your wait timeout set on the DB server.
Some times it defaults to 10 seconds. This looses the connection in 10 seconds.
mysql> show global variables like '%time%' ;
update it make it something like 28800
mysql> SET GLOBAL wait_timeout = 28800;
I've been having this issue also for about 8-9 days.
Here's some background: I'm developing a simple Java application that runs in bash.
Details:
Spring 2.5.6
Hibernate3.2.3.ga
With maven.
(The base of the project is from mkyong.com , the spring tutorial without anotations )
MySQL version:
[jvazquez#archbox ~]$ mysql --version
mysql Ver 14.14 Distrib 5.5.9, for Linux (i686) using readline 5.1
Linux archbox 2.6.37-ARCH #1 SMP PREEMPT Fri Feb 18 16:58:42 UTC 2011 i686 Intel(R) Core(TM)2 Quad CPU Q8200 # 2.33GHz GenuineIntel GNU/Linux
The application works fine in Arch Linux, Mac OS X 10.6, and FreeBSD 7.2.
When I moved the jar file to another arch linux in a different host, using the same mysql, a similar my.cnf, and the similar kernel version, the connection died and obtained the same error as the original poster:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException:
Communications link failure
I tried every possible combination for this that I found on so and the forums (http://forums.mysql.com/read.php?39,180347,180347#msg-180347 for example, which is closed now and I can't post .. ), specifically:
Triple check that I wasn't using skip
networking. (verified with ps aux
and the my.cnf)
Tried enable log_warnings=1 in the my.cnf but obviously, I wasn't hitting the
server so I didn't saw anything while using the app
SHOW ENGINE innodb STATUS didn't show anything at all; during the tests I could connect via shell, and php also connected to the mysql server
/etc/hosts has localhost 127.0.0.1
Tried the jdbc properties using localhost and 127.0.0.1 with no results
Tried adding c3p0 and changed the max_wait
Max connections in the my.cnf was changed to 900 , 2000 and still nothing my.cnf
Added wait_timeout = 60 my.cnf
Added net_wait_timeout = 360 my.cnf
Added the destroy-method="close" spring.xml
As it was pointed out (if you look up for the same exception , you will find several so threads about the issue Reproduce com.mysql.jdbc.exceptions.jdbc4.CommunicationsException with a setup of Spring, hibernate and C3P0
for example ).
If you are using tomcat, please check the security exception (again, it is on SO, you will find it )
Check that you can resolve that url that you are using
Try adding c3p0.
Verify that there isn't a firewall rejecting your connections
Finally , if you are using GNU/Linux ( ARch linux for example and you indeed obtain this exception )
Try
MySQL Forums :: JDBC and Java :: EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost
If the link get's removed, just add mysqld:ALL to /etc/hosts.allow
I know that is a bit extense, but it may help anybody using GNU/Linux and having this exception and this thread seemed the best place to post my research.
Hope it helps
I got the same error
but then I figured it out its because the Mysql server is not running at that time.
So to change the status of the server
Go to Task Manager
Go to Services
then search for your Mysql server(eg:for my case its MYSQL56)
then you will see under the status column it says its not running
by right clicking and select start
Hope this will help.
We have a piece of software (webapp with Tomcat) using Apache commons connection pooling, and worked great for years. In the last month I had to update the libraries due to an old bug we were encountering. The bug had been fixed in a recent version.
Shortly after deploying this, we started getting exactly these messages. Out of the thousands of connections we'd get a day, a handful (under 10, usually) would get this error message. There was no real pattern, except they would sometimes cluster in little groups of 2 to 5.
I changed the options to on the pool to validate the connection every time one is taken from or put back in the pool (if one is found bad, a new one is generated instead) and the problem went away.
Have you updated your MySQL jar lately? It seems like there may be a new setting that didn't used to be there in our (admittedly very old) jar.
I agree with BalusC to try some other options on your config, such as those you're passing to MySQL (in addition to the connection timeout).
If this failure is transient like mine was, instead of permanent, then you could use a simple try/catch and a loop to keep trying until things succeed or use a connection pool to handle that detail for you.
Other random idea: I don't know what happens why you try to use a closed connection (which exception you get). Could you be accidentally closing the connection somewhere?
Ensure skip-networking is commented out in my.cnf/my.ini
As BalusC mentioned, it would be very useful to post the full stacktrace (always post a full stacktrace, it is useless and frustrating to have only the first lines of a stacktrace).
Anyway, you mentioned that your code was working fine and that this problem started suddenly to occur without any code change so I'm wondering if this could be related to you other question Problem with not closing db connection while debugging? Actually, if this problem started while debugging, then I think it is (you ran out of connections). In that case, restart you database server (and follow the suggestions of the other question to avoid this situation).
I encountered same problem. I am using spring & dbcp & mysql 5.5But If I change localhost to 192.168.1.110 then everything works. What make things more weird is mysql -h localhost just works fine.
update: Finally found a solution. Changing bindaddress to localhost or 127.0.0.1 in my.conf will fix the problem.
In my case, the local loopback interface wasn't started, so "localhost" couldn't be resolved.
You can check this by running "ifconfig" and you should see an interface called "lo". If it is not up, you can activate it by running "ifup lo" or "ifconfig lo up".
In my case, the mysql.com downloaded Connector/J 5.1.29 .jar had this error whereas the 5.1.29 .jar downloaded from the MvnRepository did not.
This happened when building a Google appengine application in Android Studio (gradle, Windows x64), communicating to a Linux MySQL server on the local network/local VM.
I see you are connecting to a remote host. Now the question is what type of a network are you using to connect to the internet?
WINDOWS
If it's a mobile broadband device then get your machines IP address and add it to your hosting server so that your host server can allow connections coming from your machine.[your host might have turned this off due to security reasons].
Note that every time you use a different network device your IP changes.
If you are using a LAN then set a static IP address on your machine then add it to your host.
I hope this helps!! :)
I got the communications failure error when using a java.sql.PreparedStatement with a specific statement.
This was running against MySQL 5.6, Tomcat 7.0.29 and JDK 1.7.0_67 on a Windows 7 x64 machine.
The cause turned out to be setting an integer to a string parameter and a string to an integer parameter then trying to perform executeQuery on the prepared statement. After I corrected the order of parameter setting the statement performed correctly.
This had nothing to do with network issues as the wording of the error message suggested.
The escential problem is that Mysql JDBC pool connections is not used, then the Timeout from Mysql, close the Connections. You need change the pool Parameters to get restart connection when the connection has failures, on this way:
Connection Validation: Required (Check)
Validation Method: autocommit
You can change the Validation Method if you cannot get it works!
If you use WAMP, make sure it is online. What I did was, first turned my firewall off, then it worked, so after that I allowed connection for all local ports, specially port 80. Than I got rid of this problem. For me it was the Firewall who was blocking the connection.
I had the same problem and I used most of the params (autoreconnect etc..), but didn't try the (test_on_idle, or test_on_connect) , I am going to do them next.
However, I had this hack that got me through this:
I have a cron job called Healthcheck, It wakes up every 10 mins and makes a REST API call to the server. The web / app server picks this up, connects to the db, makes a small change and comes back with a 'yes all quiet on western front' or 'shitshappening'. When the latter, it sends a pager / email to the right people.
It has the side effect of always keeping the db connection pool fresh. So long as this cron is running, I don't have the db connection timeout issues. otherwise, they crop up.