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Re: How to store fixed size images?

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On Jun 19, 2014, at 11:21 AM, Andy Colson wrote:

> I think it depends on how you are going to use them.  I, for example, have lots of images that are served on a web page, after benchmarks I found it was faster to store them on filesystem and let apache serve them directly.

I rarely store images like that locally now; I just toss them onto Amazon S3.

When I did have to store lots of images locally , I found this to be the best method:

1. The Postgres record for the image is given a unique and random hash as a hexdigest
2. The Image is saved onto a filesystem into a directory mapped by the hexdigest

for example, there might be something like this:

	Postgres:
	id	| filename | hash
	001 | image.jpg | abcdef123

	Filesystem
	abc/def/123/abcdef123-image.jpg

	nginx/apache rewrite rule :
	abcdef123-image.jpg ->  abc/def/123/abcdef123-image.jpg

the reason for this has to do with the performance of various filesystems and issues with the distribution of digits in a sequence.  it ties into Benford's Law ( http://en.wikipedia.org/wiki/Benford's_law ) as well.

a handful of filesystems exhibit decreased performance as the number of items in a directory increases.  a few years ago, 1k-4k items was a safe max -- but at 10x that some filesystems really slowed.  i think most modern filesystems are still quick at the 5-10k range.  

a hash has more characters and a more normal distribution than a series of numbers or natural language filenames.

and if you group a hexdigest into triplets , you get 4096 max files/folders in a directory  which is a decent sweet spot
	16 * 16 * 16 = 4096

i haven't had to deal with this sort of stuff in almost 10 years now.  but archiving content like this back then was a considerable improvement to filesystem performance and web serving.


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