Here's an example from the last couple of days which is fully my own work, so I can share!

I was analysing a big data flow - yesterday's web log file in this case - and it was rather harsh on the server. No big shock about that - the log file's around 40Mbytes per day and I didn't have it in anything other than a normal text file. But it was rather silly to analyse it every time as the data only changes once every 24 hours.

Solution - let it run slowly the first time it's used after the log files are cycled, but then store the results in a cache and replay it from there each time. A user won't notice the first hit being slow if he can then call up other variants of the page at the blink of an eye!

You can try the code here (separate window) and chances are it will be very fast for you, as someone else will probably have been there recently. If not, the first time it will be slow then it will be fast. Full source code is available here.

Salient points:

1.
if (filemtime("ac_20090522") > @filemtime("cache_0.txt")) {

"is the log file newer that any cache." In the live demo, I have changed the code slightly to pick up yesterday's data every time. Note the "@" to suppress the warning message from filemtime if the cache file doesn't exit

2.
$fho = fopen("cache_0.txt","w");
fputs($fho,"$lines<%%>$result1<%%>$result2<%%>$result3\n");
fclose($fho);
}
# ------------- End of Code to set up cache --------------

"save the results to the cache". All the work of analysis has been done and the data for all the reports that might be called up for the next day is dumped into a file and then ...

3.
$parts = explode("<%%>",file_get_contents("cache_0.txt"));

"read back all the results from the cache". Note that I have NOT added a conditional - even if the cache file has just been generated, I let my code re-read it. Really I did that for testing purposes, but there's no harm in calling it back as - remember - reading the cache is FAST.

4.
Don't forget to make the cache file writable by the PHP!
(written 2009-05-24, updated 2009-05-26)

 H307 - PHP - Web2 and caching
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