My application makes queries to MySQL using JDBC. Sometimes, while a query is running, connectivity will be lost to the server. Rather than detecting this and throwing an exception, the code hangs until the TCP connection finally times out (which takes over 10 minutes)
Setting a query timeout doesn't work. If the DB server stays up this will timeout queries, but does nothing if the server goes down before the timeout triggers.
Setting socketTimeout in the MySQL connection string or invoking .withNetworkTimeout on the Connection object sort of works. This does force the connection to timeout if no response is received after the specified timeout, however it will also kill queries that run longer than the timeout even if the DB server is up. I want to die fast if the DB server goes down but still be able to run long queries.
If I could get at the sockets Keepalive settings so I could set the interval/number of probes lower and that would solve the problem, but I can't see anyway to do that with the MySQL JDBC driver.
How can I cause queries to fail quickly when the DB server goes down, while still being able to run long queries?
Related
I'm looking into aborted connection -
2022-11-21T20:10:43.215738Z 640870 [Note] Aborted connection 640870 to db: '' user: '' host: '10.0.0.**' (Got timeout reading communication packets)
My understanding is that I need to figure out whether it is an interactive or not connection, and increase wait_timeout (or interactive_timeout) accordingly. If it has no effect, then I'll need to adjust net_read_timeout or net_write_timeout and see.
I'd like to ask:
Is there a meta table that I can query for the connection type
(interactive or not)?
There are how-to's on the internet on adjusting wait_timeout (or
interactive_timeout) and all of them have rebooting the database as
the last step. Is that really required? Given that immediate effect
is not required, the sessions are supposed to come and go, and new
sessions will pick up the new value (after the system value is set),
I suppose if there is a way to track how many connections are left
with the old values, then it will be ok?
Finally, can someone suggest any blog (strategy) on handling aborted
connection or adjusting the timeout values?
Thank you!
RDS MySQL version 5.7
There is only one client that sets the interactive flag by default: the mysql command-line client. All other client tools and connectors do not set this flag by default. You can choose to set the interactive flag, because it's a flag in the MySQL client API mysql_real_connect(). So you would know if you did it. In some connectors, you aren't calling the MySQL client API directly, and it isn't even an option to set this flag.
So for practical purposes, you can ignore the difference between wait_timeout and interactive_timeout, unless you're trying to tune the timeout of the mysql client in a shell window.
You should never need to restart the MySQL Server. The timeout means the client closed the session after there has been no activity for wait_timeout seconds. The default value is 28800, which is 8 hours.
The proper way of handling this in application code is to catch exceptions, reconnect if necessary, and then retry whatever query was interrupted.
Some connectors have an auto-reconnect option. Auto-reconnect does not automatically retry the query.
In many applications, you are borrowing a connection from a connection pool, and the connection pool manager is supposed to test the connection before returning it to the caller. For example running SELECT 1; is a common test. The action of testing the connection causes a reconnect if the connection was not used for 8 hours.
If you don't use a connection pool (for example if your client program is PHP, which doesn't support connection pools as far as I know), then your client opens a new connection on request, so naturally it can't be idle for 8 hours if it's a new connection. Then the connection is closed as the request finishes, and presumably this request lasts less than 8 hours.
So this comes up only if your client opens a long-lived MySQL connection that is inactive for periods of 8 hours or more. In such cases, it's your responsibility to test the connection and reopen it if necessary before running a query.
I am running two EC2 instances on AWS to serve my application one for each. Each application can open up to 100 connections to MySql for default. For database I use RDS and t2.medium instance which can handle 312 connections at a time.
In general, my connection size does not get larger than 20. When I start sending notifications to the users to come to the application, the connection size increases a lot (which is expected.). In some cases, MySql connections increases unexpectedly and my application starts to throw PoolExhaustedException:
PoolExhaustedException: [pool-7-thread-92] Timeout: Pool empty. Unable to fetch a connection in 30 seconds, none available[size:100; busy:100; idle:0; lastwait:30000].
When I check the database connections from Navicat, I see that there are about 200 connections and all of them are sleeping. I do not understand why the open connections are not used. I use standard Spring Data Jpa to save and read my entities which means I do not open or close the connections manually.
Unless I shut down one of the instance and the mysql connections are released, both instances do not response at all.
You can see the mysql connection size change graphic here, and a piece of log here.
I have aplications that connect to a remote server (MySQL 5.5 on Windows Server 2012), at first I started receiving "too many connections" message which I solved by increasing MAX_CONNECTION value in my.inf to 500, then I start getting "can't create new thread" message so I decrease decrease timeouts to avoid idle connections using a socket, which didn't completely work. Now I get odd messages like 'file not found', as soon as I restart the service I stop getting the messages and everything works correctly.
The problem occurs when the server reaches around 170 connections at the same time.
Is there some configuration I'm missing?, I really don't know what info you need to give me a hint to fix this. I mean, there are servers that accept a lot morw of connections at the same time, right? waht I'm missing.
RAM and CPU of the system dosen't reach 35-40% at max connections (170).
Edit: Error occur at 2 'places', when running a query or at the attempt of conennection, it's like the MySQL service rejects the attempt. VB6 is the language used in the client app (ODBC connector). The app opens, executes and closes the connection.
Note: I have full control over client app and server config.
I've a MySQL 5.1.41 Server installed on a Ubuntu machine. I get connected to it through Workbench from my Windows machine over TCP/IP. I run a bigger query, after 900 seconds I got the below message, (there is no wait_timeout defined in the server's configuration file my.cnf)
Error Code: 2013. Lost connection to MySQL server during query
But when I look into the process list by using show processlist; command, I can still see my query running.
I got this link http://dev.mysql.com/doc/refman/5.0/en/gone-away.html where I found the below lines,
The problem on Windows is that in some cases MySQL does not get an
error from the OS when writing to the TCP/IP connection to the server,
but instead gets the error when trying to read the answer from the
connection.
I'm not sure whether this is the reason for my observation.
Please clarify me on this.
Thanks in advance!!
Closing connection is not a reason to stop a query. A query might be update, or kind of transaction, or select with output to remote (server) file.
Closed connection is just is just means, that you will not receive any data from DBMS after executing query (data, timings - nothing).
The reason of closing connection could be different, as SO-User posted. Try increasing
on server side:
wait_timeout
max_allowed_packet
on client side:
any kinds of timeout you find in your client (i.e. that SO-User suggests)
Do not forget to reload DBMS config and restart client (for sure)
In MySQL WorkBench we have an option to change timeout.
Find it under
Edit → Preferences → SQL Editor → DBMS connection read time out (in seconds): 600
Changed the value to 6000 or something higher.
Update
Lost connection to MySQL server
There are three likely causes for this error message.
Usually it indicates network connectivity trouble and you should check
the condition of your network if this error occurs frequently. If the
error message includes “during query,” this is probably the case you
are experiencing.
Sometimes the “during query” form happens when millions of rows are
being sent as part of one or more queries. If you know that this is
happening, you should try increasing net_read_timeout from its default
of 30 seconds to 60 seconds or longer, sufficient for the data
transfer to complete.
More rarely, it can happen when the client is attempting the initial
connection to the server. In this case, if your connect_timeout value
is set to only a few seconds, you may be able to resolve the problem
by increasing it to ten seconds, perhaps more if you have a very long
distance or slow connection. You can determine whether you are
experiencing this more uncommon cause by using SHOW GLOBAL STATUS LIKE
'Aborted_connects'. It will increase by one for each initial
connection attempt that the server aborts. You may see “reading
authorization packet” as part of the error message; if so, that also
suggests that this is the solution that you need.
If the cause is none of those just described, you may be experiencing
a problem with BLOB values that are larger than max_allowed_packet,
which can cause this error with some clients. Sometime you may see an
ER_NET_PACKET_TOO_LARGE error, and that confirms that you need to
increase max_allowed_packet.
Doc link: Error lost connection
and also check here
for some reason when I open a connection the the Percona MySQL database on my HostGator website, after fetching the query, it will disconnect/ close the connection about 10 seconds later.
I typically wouldn't care, but HeidiSQL freezes up, preventing exporting or sorting the returned rows with it's UI unless I connect again.
Any thoughts on making the connection last longer? is it something I can do myself, or will it require a dedicated server or some upgrade? (I'm currently on a shared one). Thanks!
Sounds like it may be the "wait" timeout on the MySQL connection.
SHOW VARIABLES LIKE 'wait_timeout'
That's the amount of time (in seconds) that MySQL will leave the session (the database connection) open while it's idle, waiting for another statement to be issued. After this amount of time expires, MySQL can close the connection.
You should be able to change this for a session, to change the timeout to 5 minutes
SET wait_timeout = 300
Verify the setting with the SHOW VARIABLES statement again.
NOTE: This is per connection. It only affects the current session. Every new connection will inherit their own wait_timeout value from the global setting.
(This is only a guess. There's insufficient information in the question to make a precise diagnosis. It could be something other than MySQL server that's closing the database connection, e.g. it could be your connection pool settings (if you are using a connection pool).