convert pdf to png

[Carl K]

Diez B. Roggisch wrote:
> Carl K schrieb:
>> Grant Edwards wrote:
>>> On 2007-12-24, Carl K <carl at personnelware.com> wrote:
>>>
>>>>> If it is a multi page pdf Imagemagick will do:
>>>>>
>>>>> convert file.pdf page-%03d.png
>>>> I need python code to do this.  It is going to be run on a
>>>> someone else's shared host web server, security and
>>>> performance is an issue.  So I would rather not run stuff via
>>>> popen.
>>>
>>> Use subprocess.
>>>
>>> Trying to eliminate popen because of the overhead when running
>>> ghostscript to render PDF (I assume convert uses gs?) is about
>>> like trimming an elephants toenails to save weight.
>>>
>>
>> maybe, but I wouldn't be so sure.
>>
>> currently the pdf is created in a python StringIO buffer and returned 
>> to the browser;  so it never becomes a file.  using convert means I 
>> have to first save it as a file, convert from file to file, read the 
>> file, delete the 2 files. so 6 file operations where before there were 
>> none.  That may be more of a load than the ghostscript part.
> 
> So what? I'm not sure about current HD speeds, but a couple of years ago 
> these were about 30MByte/s - and should be faster today. Which equals 
> 240MBit/s, much more than your user's internet connection. and this is 
> raw IO speed, not counting disk caches.

server is doing a ton of SQL queries (yes, moving to a 2nd box would be nice. 
might happen mid 2008) so adding HD is an issue.  not sure how much, but enough 
to try to avoid it.

> 
> In other words: given the overall latency of a network connection, your 
>  file operations shouldn't shave off more than a split-second. 

those split seconds can add up.  The server is aleady overloaded, so adding more 
is a big no no.

 > So if you
> _can_ go the subprocess-road, do it. It's the easiest way. And withou 
> further knowledge of the GS-library (that you lack, as do I) - how do 
> you know that it works "in memory", and doesn't actually expect a 
> file-name or pointer?

I am willing to take that chance.  much better than the 6 hits I know would 
happen using

I have a feeling if I have to create a file, we will go with plan B: send the 
client a pdf and let the user deal with it.  Not as nice and slick, but won't 
bog the server.

Carl K