Mysql Query Results
some times a get max_user_connections exceeds and ispite of this i can make a connection and other thing is how many currently connections being used . how do i know that please help.
The ‘max_used_connections’ variable defines the total number of connections that have been in use simultaneously since the server was started.
This variable is different when compared to the variable ‘max_connections’.
The system variable ‘max_connections’ defines the maximum permitted number of simultaneous connections by a client.
You can find the maximum connections after which the connections will be refused by using the formula (Max_used_connections/max_connections). You can refer various monitoring services like MONyog which defines these terms well.
Related
Too many connection problem in laravel5.8 application
You can see there 54k+ connection in mysql and 32 is in used only
how to remove unused connection so my application work fast.
Neither 54K connections since startup, nor a max of 32 connections simultaneously doing something, is "too many".
What is the real problem? Sluggishness? Find the slowest queries and let's work on speeding them up. Run SHOW FULL PROCESSLIST to see if any queries have been running for more than a few seconds; they are a prime candidate for optimizing. Or use the slowlog.
Connection is just a "count" of attempted connections. It does not relate to active connections nor max_used_connections.
Run the following commands simultaneously:
SHOW VARIABLES LIKE 'max_connections'
SET GLOBAL max_connections = 1000000;
Connection is just a "count" of attempted connections. It does not relate to active connections nor max_used_connections.
See MySQL show status - active or total connections?
If you really are having many current open connections, you should look into what these connections are. You might have a sub-optimal query in your code or a bot is spamming an open endpoint.
You can see process list by running the query
show processlist;
You can then kill connections for the short term solution or take care of whatever problem was causing the connections in the first place.
If you really do need that many connections (doubt it), you should look into scaling your database instance, e.g. by adding read replicas.
I try to import an 1.4G mysql file into aws rds. I tried the 2 cpu and 4G mem option. I still got error: Lost connection to MySQL server during query. My quetion is that how do I import large mysql file into rds.
MySQL Server and the MySQL client both have a parameter max_allowed_packet.
This is designed as a safety check to prevent the useless and disruptive allocation of massive amounts of memory that could occur if data corruption caused the receiving end of the connection to believe a packet¹ to be extremely large.
When transmitting queries and result sets, neither client nor server is allowed to send any single "thing" (usually a query or the value of a column) that is larger than max_allowed_packet -- the sending side will throw an error and refuse to send it if you try, and the receiving side will throw an error and then close the connection on you (so the client may or may not actually report the error thrown -- it may simply report that the connection was lost).
Unfortunately, the client setting and server setting for this same parameter are two independent settings, and they are uncoordinated. There is technically no requirement that they be the same, but discrepant values only works as long as neither of them ever exceeds the limit imposed by the other.
Worse, their defaults are actually different. In recent releases, the server defaults to 4 MiB, while the client defaults to 16 MiB.
Finding the server's value (SELECT ##MAX_ALLOWED_PACKET) and then setting the client to match the server (mysql --max-allowed-packet=max_size_in_bytes) will "fix" the mysterious Lost connection to MySQL server during query error message by causing the client to Do The Right Thing™ and not attempt to send a packet that the server won't accept. But you still get an error -- just a more informative one.
So, we need to reconfigure both sides to something more appropriate... but how do we know the right value?
You have to know your data. What's the largest possible value in any column? If that's a stretch (and in many cases, it is), you can simply start with a reasonably large value based on the longest line in a dump file.
Use this one-liner to find that:
$ perl -ne '$max = length($_) > $max ? length($_) : $max; END { print "$max\n" }' dumpfile.sql
The output will be the length, in bytes, of the longest line in your file.
You might want to round it up to the next power of two, or at least the next increment of 1024 (1024 is the granularity accepted by the server -- values are rounded) or whatever you're comfortable with, but this result should give you a value that should allow you to load your dump file without issue.
Now that we've established a new value that should work, change max_allowed_packet on the server to the new value you've just discovered. In RDS, this is done in the parameter group. Be sure the value has been applied to your server (SELECT ##GLOBAL.MAX_ALLOWED_PACKET;).
Then, you'll need to pass the same value to your client program, e.g. mysql --max-allowed-packet=33554432 if this value is smaller than the default client value. You can find the default client value with this:
$ mysql --help --verbose | grep '^max.allowed.packet'
max-allowed-packet 16777216
The client also allows you to specify the value in SI units, like --max-allowed-packet=32M for 32 MiB (33554432 bytes).
This parameter -- and the fact that there are two of them, one for the client and one for the server -- causes a lot of confusion and has led to the spread of some bad information: You'll find people on the Internet telling you to set it to ridiculous values like 1G (1073741824, which is the maximum value possible) but this is not a really good strategy since, as mentioned above, this is a protective mechanism. If a packet should happen to get corrupted on the network in just the wrong way, the server could conclude that it actually needs to allocate a substantial amount of memory just so that this packet can successfully be loaded into a buffer -- and this could lead to system impairment or a denial of service by starving the system for available memory.
The actual amount of memory the server normally allocates for reading packets from the wire is net_buffer_length. The size indicated in the packet isn't actually allocated unless it's larger than net_buffer_length.
¹ a packet refers to a layer 7 packet in the MySQL Client/Server Protocol sense. Not to be confused with an IP packet or datagram.
Your connection may timeout if you are importing from your local computer or laptop or a machine which is not in the same region as the RDS instance.
Try to import from an EC2 instance, which has access to this RDS. You will need to the upload the file to S3, ssh into the EC2 instance and run an import into RDS.
I am have a trouble with my database, I set up the max_user_connections to 800 and the issue persist, "User root already has more than 'max_user_connections' active connections" I would like to know if there is a limit for max_user_connections, Can I set 10000 and that is not going to break my database ?
¿ how can i know the limit ?
If I run SHOW PROCESSLIST and Get this, All is right ?
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To see what is the max connnections for a user use the vairable in information_schema for your mysql database to see global configuration for this.
SHOW VARIABLES LIKE "max_user_connections";
If it is zero, then it is no limit otherwise the limit is set to the one as response.
If you want to check for particular user, use this
SELECT max_user_connections FROM mysql.user WHERE user='db_user' AND host='localhost';
Now for your question what is the effect on increasing this, As per
http://www.electrictoolbox.com/update-max-connections-mysql/
Note that increasing the number of connections that can be made will
increase the potential amount of RAM required for MySQL to run.
Increase the max_connections setting with caution!
So here max_connections is total number of connections allowed from all users.
Also i would suggest to use connection pool so that the size of pool is fixed and it will be from that only and is not growing. Also make sure it is returned back to pool once the work is done.
Too many active connections
The problem you are having is because you are not closing previous connections you have used to access the database. (And its also likely that you are running many separate queries that could all be compressed into a single query)
From looking at your error message, "User root" has more than the max available connections. There aren't 800 different people accessing the database, you are accessing the database 800 different times and not cleaning up afterwards.
I'm getting following error when I try to log onto phpMyAdmin.
User ** already has more than 'max_user_connections' active connections
Could anyone let me know how to close these DB connections from MySQL server end?
Thank you for your time!
Read max_connections document to solve your problem
If clients encounter Too many connections errors when attempting to
connect to the mysqld server, all available connections are in use by
other clients.
The permitted number of connections is controlled by the
max_connections system variable. The default value is 151 to improve
performance when MySQL is used with the Apache Web server. To support
more connections, set max_connections to a larger value.
First: Check your current database max_connection variable
SHOW VARIABLES LIKE 'max_connections';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 151 |
+-----------------+-------+
Then Try to increase the max_connection parameter either with running command like:
SET GLOBAL max_connections = 300;
Or set this parameter in my.cnf that mostly is located at /etc/my.cnf
vi /etc/my.cnf
max_connections = 300
Finally: Restart MySQL service
FYI
you can also check max_user_connections. however, they are related like this:
max_connections set the total connection limit
max_user_connections set limit per user
====
As Sushilzzz asked: can this be caused by low RAM?
Short answer: No
Long Answer: yes, If Ram Size is low and MySQL can't respond as fast as needed there will be many open connections and you can easily hit the max connection.
The estimated number of max connections per 1GB of ram is 100 (if you don't have any other process using ram at the same time). I usually use ~75 for max_connection per 1GB of RAM
RAM max_connection
1GB 70
2GB 150
4GB 300
8GB 500
This happens due to limit specified in the mysql configuration, the system variable max_user_connections.
Solutions
Killing the queries which are stuck at the backend is only a solution I would suggest if it is a SELECT query. Queries that change data, like UPDATE/DELETE/INSERT, are not to be killed.
Secondly, you can use the command mysqladmin processlist to check what is going on inside mysql.
If locking is causing your problem, you can check which engine you are using and change it to another. IBM's SolidDB documentation on table locks might help you. Though there may be another reason for this. (For example, perhaps your queries are taking too long because of an unoptimized query, or the table size is too big, or you have a spammed database).
Your best bet is to increase max_connections. For a MySQL instance serving multiple different web apps (raw php, WordPress, phpBB), you probably want a value of at least 60 for this.
Issue this command and you'll find out how many global connections you have available:
show global variables like '%connections%'
You can find out how many connections are in use at any given moment like this:
show status like '%connected%'
You can find out what each connection is doing like this:
show full processlist
I would try for a global value of at least 100 connections if I were you. Your service provider ought to be able to help you if you don't have access to do this. It needs to be done in the my.cnf file configuration for MySQL. Don't set it too high or you run the risk of your MySQL server process gobbling up all your RAM.
A second approach allows you to allocate those overall connections to your different MySQL users. If you have different MySQL usernames for each of your web apps, this approach will work for you. This approach is written up here. https://www.percona.com/blog/2014/07/29/prevent-mysql-downtime-set-max_user_connections/
The final approach to controlling this problem is more subtle. You're probably using the Apache web server as underlying tech. You can reduce the number of Apache tasks running at the same time to, paradoxically, increase throughput. That's because Apache queues up requests. If it has a few tasks efficiently banging through the queue, that is often faster than lots of tasks because there's less contention. It also requires fewer MySQL connections, which will solve your immediate problem. That's explained here: Restart Mysql automatically when ubuntu on EC2 micro instance kills it when running out of memory
By the way, web apps like WordPress use a persistent connection pool. That is, they establish connections to the MySQL data base, hold them open, and reuse them. If your apps are busy, each connection's lifetime ought to be several minutes.
First, this is a hack, but works, especially on a shared host.
We all have bad "neighbors" sometimes, right?
If you have access to your /etc/ increase the limit from 30 to 50, in your my.cnf or through the information schema.
To ignore the error message the visitor might see, use #mysql_connect().
If there are more than 30 MUCs, use the "or die()" statement to stop the query.
Replace the "or die" message with die(header(location: THIS PAGE)) and be sure to mysql_close();
Yes, it will cause a delay in page loading. But better to load than a white screen of death -or worse error messages that visitors have no understanding of.
It looks like queries stuck on the server. Restart and everything will be ok.
If you are on shared hosting, just contact your hosting provider they will fix it.
I'm namecheap user and they solved it.
In my case 1 have a limit of 10 user connections; And I do not have the right to change the max user connections variable. You can check the amount user connection like so.
show variables like "max_user_connections";
You can set the max amount of user connections like so if you have permission.
SET GLOBAL max_connections = 300;
Else you can view the processes in use like so
Show full processlist;
And kill some of the process with I like so. In you case replace number by a id in previous table Show full processlist;
kill 10254745;
Is there a limit to the maximum number of concurrent users connected to SQL Server 2008? I am guessing computer resources determine that limit (if it exists), but I am also wondering if there is a theoretical limit. I have tried googling the answer, but all the information I have found is based upon earlier versions of SQL Server. If there is a limit, does it apply to just a database or a SQL Server instance?
http://msdn.microsoft.com/en-us/library/ms143432.aspx
User connections: 32767