[TYPO3-performance] TS-Rendering - IMG_RESOURCE - 622 ms - Solution

[bernd wilke]

Am Fri, 25 Sep 2009 14:44:18 +0200 schrieb JoH asenau:

>> the modified time is not available on windows, right? Otherwise
>> checking mtime should be ok?!
> 
> At least on our 2K VBox, XP VBox and Vista Ultimate master I can see
> "Geändert" and "Erstellt" - so I guess there is a "modified time"
> available.

Windows stores time of creation, last modification and last access so 
they are not all visible at the same time.

> On the other hand this might still not increase performance
> as long as the check for the file content isn't done in the second run,
> because the content might still be the same, even though the time has
> changed.
> 
> So I would prefer the following concept:
> 
> if (time has changed && size has changed) {
>     create new image
> } else if (time has changed && content has changed) {
>     create new image
> }
> 
> But this is just based on 2 assumptions: 1. checking for a change of
> content will be faster than just generating a new image.
> 2. if the size is different the content can't be the same
> 
> If 1. is not the case a simple check for the time should be enough.

maybe the content-check can be done in two steps:
1. check a small part of the file
2. check complete file

for pictures the first x KB are likely to change if the complete picture 
changes (assuming most formats store filesize in the fist bytes)

in future we may need a similar check for movies (new media-support) and 
that might be very big files. 
Calculating md5 for all bytes of the whole file will take a long time. 

firsth thoughts for faster checks: 
- check first and last x MB (md5)
- every x MB check a part of y KB 
	build md5 of subparts (c) and skip the rest (s):
	cssssscssssscssssscsssscssssscsss



bernd
-- 
http://www.pi-phi.de/cheatsheet.html