Synchronization

r_honey

My Hosting provider puts a limit on the maximum no. of simultanoeus DB connections. So, I am providing a wrapper to my DB layer through which all modules request new DB connections to keep a check on the permissible maximum...

I need to make sure that only one script, page or thread (whatever you call it) is executing inside the Request connection method of the wrapper.

So, is there any built-in support for synchronization in PHP like there is synchronized construct in Java...

MarkR

This is seriously messed up.

Provided your pages only use one database connection at a time, your provider should configure their web server so that with as many executing as the web server is prepared to run at once, you still won't exceed the database connections.

This is the right way.

Attempting to synchronise them with locks is wrong.

Yes, you COULD do it. The easiest way is to lock a file with flock(). But don't.

Get a decent provider.

The provider is either providing too few connections, or allowing too many web server processes - this demonstrates that they're incompetent.

Mark

r_honey

Can you elaborate more on when you say

your provider should configure their web server so that with as many executing as the web server is prepared to run at once, you still won't exceed the database connections.

I have a reputed provider. Its just that I am getting fancy with my code.
None of my pages open more than a couple of connections at a time. Suppose the provider provides 50 max. simultanoeus connection.
I know that for any decent site, that limit will never be reached.

For my own practise, all my pages request connection via a pooled class, that returns a reference to an exception, only if the currently open number of connections for all pages together is less than 45.

In java, this is very easy to implement via Servlets & synchronized construct.

I am just trying to add synchronization to the pooled class' requestConnection method, to prevent races conditions in manipulating the static connCount variable.

MarkR

r_honey wrote:
For my own practise, all my pages request connection via a pooled class, that returns a reference to an exception, only if the currently open number of connections for all pages together is less than 45.

Connection pooling is not possible with PHP, due to its shared-nothing model.

You can't share connections between PHP instances. Open a connection at the beginning of your page, and close it at the end (or allow it to be closed).

Do not use persistent connections, EVER.

In java, this is very easy to implement via Servlets & synchronized construct.

Because Java necessarily runs inside a single process with shared memory. The "synchronised" construct does nothing to protect against other instances (potentially on other machines).

PHP uses shared-nothing, hence you can't do this kind of thing. But it is more scalable.

You should set Apache MaxClients such that MaxClients * number of connections per page is <= the maximum allowed connections. Failing to do this will result in the application breaking under load.

Mark

r_honey

Do not use persistent connections, EVER.

If it so unadvisable to use persistent connections, why are they provided by PHP in the first place???

When you say:

You should set Apache MaxClients such that MaxClients * number of connections per page is <= the maximum allowed connections.

suppose a single page sample.php is requested by two clients almost simultaneously. Does this max. no of connections apply to all instances of the pages together, or to each instance individually???