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.
Related
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.
Error displaying the error page: Application Instantiation Error: Could not connect to MySQL.
This Error is shown sometimes (one every 20 pageviews) and I tried a lot of solutions without any change.
This error found with Joomla 3.5+
This will help you do some testings...
On MySql server run this query...
show processlist;
If this shows a lot of connections then you may be hitting the max_connections problem. Try to increase that to a reasonable number. But, do not make it too much because if it goes beyond the amount of available resources on your server then it will make MySql server crash and it will become a bigger problem where your website will go offline.
Try to check if you are closing sessions properly in your scripts using session_write_close(); You can find more about this function here: http://php.net/manual/en/function.session-write-close.php
This function will write user's current session on disk to be reloaded next time and most important part it will do for you with this problem is that it will close PHP's any connection made to the MySql server, so it will free up the MySql server for next visitor to come and open another page.
Lets say if you have 150 max_connections and at the same time you get 200 visitors, then PHP will still wait for some time for another 50 connections to be free before giving a timeout error where you get "Could not connect to server". But, if sessions are not closing properly, then its so bad that 50 connections will never get processed because 150 will never go away very soon, there is a separate MySql setting for that named wait_timeout. So, any MySql connection you open will keep waiting until you close yourself in script just like you open OR until wait_timeout happens. But, if you close sessions properly then next connection will become available as soon as your PHP script has finished processing and page is generated for the user for viewing and it will make the connection seat free for next connection to come in.
Server RAM was very low!
After upgrade from 0.5GB to 2GB all the kind of error starts with Error displaying the error page: gone.
I found the problem solution by using htop while connecting to the server via SSH, after that, I start opening pages rapidly which show the error plus the htop shows that the RAM was close to full.
show processlist; were helpful to find that the problem not about the connection number.which it may sometimes cost the same error in the same way.
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
We are having an intermittent issue with connections to our mysql server timing out.
The error we are receiving is as following.
(2003, 'Can\'t connect to MySQL server on \'<connection>\' ((2013, "Lost connection to MySQL server during query (error(104, \'Connection reset by peer\'))"))')
Callstack:
File "/usr/lib64/python2.7/site-packages/pymysql/connections.py", line 818, in _connect
2003, "Can't connect to MySQL server on %r (%s)" % (self.host, e))
File "/usr/lib64/python2.7/site-packages/pymysql/connections.py", line 626, in __init__
self._connect()
Some more info:
We have a flight of EC2 servers that are constantly running queries to a backend RDS.
We average about 500 connections per second to the RDS
We have around 0 - 4 hiccups per RDS per day
The hiccups don't correspond with our maintenance window
When we hit a hiccup it can affect quite a few connections ~50
When a hiccup happens it will disrupt connections across all servers and ports
The error itself looks to be generated from the tcp connection being closed on the ec2. Our TCP keep alive time is set to 7200 seconds and that's when the error is fired off.
My question is what can be done to track down why these hiccups happen? It's great that they don't happen often, but it's not ideal that they happen at all.
Any advice would be appreciated thanks!
Update 10/29:
I've been running a service checking to see if I have any long processes running on the sql server and it looks like these errors aren't getting that far. A new process is never created for this connection! I have still been receiving the hiccups, just no signs of connections.
So after a back and forth with amazon support here is the current solution we have come to.
Amazon has raised our socket listen backlog by adjusting the somaxconn value on the RDS instance.
The value was at the default of 128 and has been bumped up to 1024.
Once the value was adjusted we no longer received the Lost Connection error.
I'm using Node.js to run a web-server for my web application. I'm also using the node-mysql module to interface with a MySQL server for all my persistent database needs.
Whenever there is a critical error within my Node.js application that crashes my app's process I get an email sent to me. So, I keep getting this email with an error saying "Too many connections". Here's an example of the error:
Error: Too many connections
at Function.Client._packetToUserObject (/apps/x/node_modules/mysql/lib/client.js:394:11)
at Client._handlePacket (/apps/x/node_modules/mysql/lib/client.js:307:43)
at Parser.EventEmitter.emit (events.js:96:17)
at Parser.write.emitPacket (/apps/x/node_modules/mysql/lib/parser.js:71:14)
at Parser.write (/apps/x/node_modules/mysql/lib/parser.js:576:7)
at Socket.EventEmitter.emit (events.js:96:17)
at TCP.onread (net.js:396:14)
As you can see all it tells me is that the error is coming from the mysql module, but it doesn't tell me where in my application code the issue is occurring.
My application opens a db connection anytime I need to run one or more queries. I immediately close the connection after all my queries and data has been collected. So, I don't understand how I could be exceeding the 151 max_connections limit.
Unless there is a place in my code where I forgot to call db.end() to close the connection, I don't see how my app would leak like this. Even if there was such a mistake, I wouldn't get these emails sent by the dozens. Yesterday, I received almost 100 emails with roughly the same error. How could this be happening? If my application had leaked and allocated connections over time, as soon as the first error occurred the app process would crash and all connections would be lost, preventing the app to crash again. Since I received ~100 emails, this means the app crashed ~100 times, and all within a short period of time. This could only mean that somewhere in my application a lot of connections where established in a short period of time, right?
How could I avoid this problem? This is very discouraging. All help is highly appreciated. Thanks
MySQL has a default MAX_CONNECTIONS = '100' not 151 unless you changed it. Also, in truth you have MAX_CONNECTIONS + 1. The plus 1 allows a root user to logon even after you have maxed out the conenctions in order to figure out what is actually being used. When your connections are maxed out try logging on as root and running the following command from MySQL.
mysql> SHOW FULL PROCESSLIST
Post the output of this command above. Once you actually know what is consuming your resources you can go about fixing it.It could easily be your code that is leaving open connections.
You should take a look at the follwoing documentation: Show Processlist
+1 for question. Investigations showed us that node-mysql opens the connections and doesn't close them. Because of that at one moment be reach the limit of max connections. The question is why node-mysql doesn't close the connections?