least expensive way to monitor a log file?

[sde]

i'm writing a php script which will be running with max_execution time set to 0. the sole purpose of this script is to monitor a log file and print something once the log file has been modified.

this is obviously not going to be a public app, it's only meant to be used by a single web client at a time.

so, my question is, what's the least expensive way to monitor if a log file has changed.

right now, i'm just getting the filesize and clearing the statcache in every iteration of the loop which is once per second.

any other ideas or comments on that?

[DJMaze]

don't use PHP
Systems like Windows and GNU/Linux have somesort of "listener".
In that respect nothing happens until the system gets a notification of file changes. Then the sytem will send a message to your application that "something" has changed.

As an example (that i know of): SHChangeNotifyRegister Function ()

[sde]

this is an ajax front end to system information. updating the UI through ajax is expensive, so i only want to do it when something has changed in a log file.

the system will not be able to notify the web client directly, so i will need js->php to get server-side info.

if i had a listener app writing to mysql, then php polling for changes, it would be more expensive than php just looking directly at the file.

so i guess the question was more like this: within PHP, what uses less resources, checking the file size, change time, or something else that would allow me to detect a change.

[Belisarius]

I do mtime then filesize - no sense in reading in a file if all that happened was that it was touched.

[teknomage1]

It looks like someone may have exposed a php interface to linux's inotify filesystem monitor The RoLLing cOde: Get Spread Toolkit and inotify-tools PHPized

[ShadyCraig]

There is a library available called FAM:

PHP: fam - Manual

fam_cancel_monitor -- Terminate monitoring
fam_close -- Close FAM connection
fam_monitor_collection -- Monitor a collection of files in a directory for changes
fam_monitor_directory -- Monitor a directory for changes
fam_monitor_file -- Monitor a regular file for changes
fam_next_event -- Get next pending FAM event
fam_open -- Open connection to FAM daemon
fam_pending -- Check for pending FAM events
fam_resume_monitor -- Resume suspended monitoring
fam_suspend_monitor -- Temporarily suspend monitoring

[DJMaze]

Right, that was it! I totally forgot about FAM

But, it wonder how useful it is for an AJAX driven page which is asking PHP requests all the time already. Afterall, it doesn't understand PUSH methods yet.
Maybe you can solve that using Comet

[sde]

that's for the suggestions tek and shady.. haven't got around to trying them yet but it certainly is looking good.

djm, currently i'm setting max_execution_time to 0 and executing an ajax call. php keeps the request open and once it determines there's a change, it sends a response.

javascript then handles the response and opens another request.