Yesterday I can see in the log that within 1 minute timespan, there is alot of mysql errors with too many connections failures. I am running default setting: 151 for max_connections and have not experienced this before.
When checking current state, my thread connections is only 1 and up to 3 at max.
Should i increase my max_connections or did i just temporary suffer from a DDoS?
Note: It solved itself and worked immediately after that minute.
Update 2: It just happend again. I can see multiple errors within some seconds timeframe the error log. Why does this happen?
Decrease max_connect_errors to, say, 100. This is a small protection against hackers.
Threads_running is always at least 1 because it includes your SHOW.
With max_connections = 151, Max_used_connections = 152 means that 151 user connections came in, plus one "extra" connection was allowed and used. For this reason, do not run your application as root (or any other SUPER user).
GRANT ... ON your_database.* ..., not ... ON *.* ... for any application logins. This seriously slows down hackers from getting at the mysql database.
root should be allowed only from localhost. This is another safety measure.
If your web server has an "access" log, look at it. You may see hundreds of similar looking hack attacks in a row. And you may a similar set of them often.
Be sure to escape any data coming from html forms. Do this as you build the INSERTs. Without this, you are wide open for attack.
Addenda
SELECT user, host FROM mysql.user WHERE Super_priv = 'Y';
will show you who has SUPER. As a first cut, it should include only host values of localhost, 127.0.0.1, or ::1, all of which are effectively localhost. This does not prevent hackers from first hacking the client, which may also be on localhost.
This may list those with another way in:
SELECT user, host FROM mysql.user WHERE Grant_priv = 'Y';
Back to the question
The Web server's (nginx's?) limit on the number of connections should be less than MySQL's max_connections. This will stop hackers (and users) at the door, rather than letting them clog up both the web server and MySQL.
Even on a well running system, 20 is a reasonable max for how many should be allowed into the web server simultaneously. If there are more, then they are probably stumbling over each other; it would be better to let a few get all the resources they need rather than take longer because of battling over resources.
Related
I have a MySQL database that I am running very simple queries against as part of a webapp. I have received reports from users starting today that they got an error saying that their account doesn't exist, and when they log in again, it does (this happened to only a few people, and only once to each, so clearly it is rare). Based on my backend code, this error can only occur if the same query returns 0 row the first time, and 1 row the second. My query is basically SELECT * FROM users WHERE username="...". How is this possible? My suspicion is that the hard disk is having I/O failures, but I am unsure because I would not expect MySQL to fail silently in this case. That said, I don't know what else it could be.
This could be a bug with your mysql client (Though I'm unsure as to how the structure of your code is, it could just be bad query). However let's assume that your query has been working fine up until now with no prior issues, so we'll rule out bad code.
With that in mind, I'm assuming it's either a bug in your mysql client or your max connection count is reached (Had this issue with my previous host - Hostinger).
Let's say your issue is a bug in your mysql client, set your sessions to per session basis by running this
SET SESSION optimizer_switch="index_merge_intersection=off";
or in your my.cnf you can set it globally
[mysqld] optimizer_switch=index_merge_intersection=off
As for max connection you can either increase your max_connection value (depending if your host allows it), or you'll have to make a logic to close the mysql connection after a query execution.
$mysqli->close();
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 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've hit a problem with my MySQL queries and was hoping someone could offer some help/advice.
I'm developing a PHP-based system which combines quite a lot of data in different tabs on one page (tab1 = profile, tab2 = address, tab3 = payments etc.) and as a result, one page can have up to 34/40 MySQL queries pulling from different tables or with different criteria.
The page load became really slow and I asked my web host if they knew what was wrong and they advised it's because of slow MySQL queries (some over 2 seconds). They also said that my MySQL user is only allowed 15 connections at a time.
If my page has 40 queries and only 15 connections are allowed at a time, does this mean they effectively queue and wait for one to complete? If this was the case then I can understand why the page is taking a while to load but i'm not sure of the solution. Is 15 MySQL queries considered a lot or is this quite a tight restriction by my host (HostMonster)?
Also, if there were 15 users accessing the system at the same time, would this 15 connections be split between each of them or is it 15 connections per user logged into the site? I assume they mean per database user but all people who access the system will be using the same database user so it seems impossible to create a system in which several users can access at one?
The whole connections thing has confused me a little.
Thanks in advance for any help!
Have one connection per page. Put the queries into sequence
Optimize those queries - see explain and use indexes
Perhaps combine queries to reduce the through put.
BTW 10+ queries per page is excessive IMHO.
If having max connect error problem then use this command from command line
mysqladmin flush-hosts -uuser -p'password'
this will flush hosts that MySQL has recorded and will build the list again. In the newer version of MYSQL 5.6 you get more information on this but not on previous version.
You can set the following
max_connect_errors 10000
to avoid the message to appear again.
15 queries or connection is not a problem at all, in busy databases we have seen thousand connections and tens of thousands of queries per second.
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;