If there are many requests of db server at the same time saying that the QPS is 100, and the DB server has a connection limit saing 1000, so if the requests are slow queries which will eventually got inactivity timeout, at this time what shoud i do to prevent the npm package mysql from creating new connection?
Because the npm package mysql will remove the connection object from the connection object pool with fatal error like inactivity timeout and leave space for creating new connection.
For high load, you should use connection pools with persistent connections. Those are usually available in hight level query builders and ORMs like knex and sequelize.
But if you don't want use them, you can also try native pools.
I have a project built using django 1.11 and i am sending a request from my admin view and it is creating a new DB connection on every request(using django development server, runserver).
But the same thing using gunicorn as server does not increase the number of connections in DB it uses same connection that was created in first request.
In my database settings CONN_MAX_AGE is set to 300 which is 5mins. I am sending second request within 5 mins, so it is supposed to use same connection that was created in first request.
Any idea why, with runserver, django is creating new DB connection on every request and not following persistent connections behavior of django ?
From the docs:
The development server creates a new thread for each request it
handles, negating the effect of persistent connections. Don’t enable
them during development.
Is it possible to cache database connections when using PHP like you would in a J2EE container? If so, how?
There is no connection pooling in php.
mysql_pconnect and connection pooling are two different things.
There are many problems connected with mysql_pconnect and first you should read the manual and carefully use it, but this is not connection pooling.
Connection pooling is a technique where the application server manages the connections. When the application needs a connection it asks the application server for it and the application server returns one of the pooled connections if there is one free.
We can do connection scaling in php for that please go through following link: http://www.oracle.com/technetwork/articles/dsl/white-php-part1-355135.html
So no connection pooling in php.
As Julio said apache releases all resources when the request ends for the current reques. You can use mysql_pconnect but you are limited with that function and you must be very careful. Other choice is to use singleton pattern, but none of this is pooling.
This is a good article: https://blogs.oracle.com/opal/highly-scalable-connection-pooling-in-php
Also read this one http://www.apache2.es/2.2.2/mod/mod_dbd.html
Persistent connections are nothing like connection pooling. A persistent connection in php will only be reused if you make multiple db connects within the same request/script execution context. In most typical web dev scenarios you'll max out your connections way faster if you use mysql_pconnect because your script will have no way to get a reference to any open connections on your next request. The best way to use db connections in php is to make a singleton instance of a db object so that the connection is reused within the context of your script execution. This still incurs at least 1 db connect per request, but it's better than making multiple db connects per reqeust.
There is no real db connection pooling in php due to the nature of php. Php is not an application server that can sit there in between requests and manage references to a pool of open connections, at least not without some kind of major hack. I think in theory you could write an app server in php and run it as a commandline script that would just sit there in the background and keep a bunch of db connections open and pass references to them to your other scripts, but I don't know if that would be possible in practice, how you'd pass the references from your commandline script to other scripts, and I sort of doubt it would perform well even if you could pull it off. Anyway that's mostly speculation. I did just notice the link someone else posted to an apache module to allow connection pooling for prefork servers such as php. Looks interesting:
https://github.com/junamai2000/mod_namy_pool#readme
I suppose you're using mod_php, right?
When a PHP file finishes executing all it's state is killed so there's no way (in PHP code) to do connection pooling. Instead you have to rely on extensions.
You can mysql_pconnect so that your connections won't get closed after the page finishes, that way they get reused in the next request.
This might be all that you need but this isn't the same as connection pooling as there's no way to specify the number of connections to maintain opened.
You can use MySQLi.
For more info, scroll down to Connection pooling section # http://www.php.net/manual/en/mysqli.quickstart.connections.php#example-1622
Note that Connection pooling is also dependent on your server (i.e. Apache httpd) and its configuration.
If an unused persistent connection for a given combination of "host, username, password, socket, port and default database can not be found" in the open connection pool, then only mysqli opens a new connection otherwise it would reuse already open available persistent connections, which is in a way similar to the concept of connection pooling. The use of persistent connections can be enabled and disabled using the PHP directive mysqli.allow_persistent. The total number of connections opened by a script can be limited with mysqli.max_links (this may be interesting to you to address max_user_connections issue hitting hosting server's limit). The maximum number of persistent connections per PHP process can be restricted with mysqli.max_persistent.
In wider programming context, it's a task of web/app server however in this context, it's being handled by mysqli directive of PHP itself in a way supporting connection re-usability. You may also implement a singleton class to get a static instance of connection to reuse just like in Java. Just want to remind that java also doesn't support connection pooling as part of its standard JDBC, they're being different module/layers on top of JDBC drivers.
Coming to PHP, the good thing is that for the common databases in the PHP echosystem it does support Persistent Database Connections which persists the connection for 500 requests (config of max_requests in php.ini) and this avoids creating a new connection in each request. So check it out in docs in detail, it solves most of your challenges. Please note that PHP is not so much sophisticated in terms of extensive multi-threading mechanism and concurrent processing together with powerful asynchronous event handling, when compared to strictly object oriented Java. So in a way it is very less effective for PHP to have such in-built mechanism like pooling.
You cannot instantiate connection pools manually.
But you can use the "built in" connection pooling with the mysql_pconnect function.
I would like to suggest PDO::ATTR_PERSISTENT
Persistent connections are links that do not close when the execution of your script ends. When a persistent connection is requested, PHP checks if there's already an identical persistent connection (that remained open from earlier) - and if it exists, it uses it. If it does not exist, it creates the link.
Connection pooling works at MySQL server side like this.
If persistence connection is enabled into MySQL server config then MySQL keep a connection open and in sleep state after requested client (php script) finises its work and die.
When a 2nd request comes with same credential data (Same User Name, Same Password, Same Connection Parameter, Same Database name, Maybe from same IP, I am not sure about the IP) Then MySQL pool the previous connection from sleep state to active state and let the client use the connection. This helps MySQL to save time for initial resource for connection and reduce the total number of connection.
So the connection pooling option is actually available at MySQL server side. At PHP code end there is no option. mysql_pconnect() is just a wrapper that inform PHP to not send connection close request signal at the end of script run.
For features such as connection pooling - you need to install swoole extension first: https://openswoole.com/
It adds async features to php.
After that its trivial to add mysql and redis connection pooling:
https://github.com/open-smf/connection-pool
Some PHP frameworks come with pooling built-in: https://hyperf.wiki/2.2/#/en/pool
With the node-mysql module, there are two connection options - a single connection and a connection pool. What is the best way to set up a connection to a MySQL database, using a single global connection for all requests, or creating a pool of connections and taking one from the pool for each request? Or is there a better way to do this? Will I run in to problems using just a single shared connection for all requests?
Maintaining a single connection for the whole app might be a little bit tricky.
Normally, You want to open a connection to your mysql instance, and wait for it to be established.
From this point you can start using the database (maybe start a HTTP(S) server, process the requests and query the database as needed.)
The problem is when the connection gets destroyed (ex. due to a network error).
Since you're using one connection for the whole application, you must reconnect to MySQL and somehow queue all queries while the connection is being established. It's relatively hard to implement such functionality properly.
node-mysql has a built-in pooler. A pooler, creates a few connections and keeps them in a pool. Whenever you want to close a connection obtained from the pool, the pooler returns it to the pool instead of actually closing it. Connections on the pool can be reused on next open calls.
IMO using a connection pool, is obviously simpler and shouldn't affect the performance much.
I'm developing a WebApp and it can be accessed 24/7, so it doesn't really have a moment when I can say: "Finally I'm not using the connection pool anymore, I'm going to shut it down".
I've read (here at SO: BoneCP correct usage) that I should use the shutdown method if I'm sure that I'm not using connections anymore, but that's not my case.
So, is there any problem if I don't shutdown the pool?
The answer is to allow the connection pool to manage database connections. Any decent connection pool will provide some configuration options that will enable you to customize connection retention policies, min/max pool sizes, connection testing / verification, etc. . .
I looked at your link (BoneCP correct usage) and I would suggest that you configure the connection pool at the web container level as a JNDI DataSource, and not within your application. Your application would then access then access the connection pool via JNDI. There are number of benefits to this approach. Here a few:
1) your app doesn't know or care whether it's using a connection pool or a regular jdbc connection. The latter is helpful during development testing, as startup time faster and memory usage is smaller.
2) your app doesn't need to the the database connection details (e.g. jdbc url, username, and password). Allowing you to use a common WAR file for all deployments.
3) configuration and tuning of the pool can be done without need for rebuilding and redeploying your application.