What is best practice when it comes to storing images for a gallery?

Question

My question is not about storing images on disk or in DB.

• Images will be stored on disk
• Image path and other image data will be saved in database.
• Images will be given a unique filename
• Images will be stored in 3 sizes
• In time there may be many images used by many users

My questions are:
- Should images be stored in one folder, or many folders?
- Is it ok to use md5 for creating unique id's? E.g. md5(id+filename+random_num)
- Should images be cached on server or on clients browser / computer?

Anything else I should think of?

The solution is using php, apache and mysql. We use Uploadify for uploading images.

Some code I use today

  /**
   * Calculate dir tree for object
   * Folders starts from 00 to FF (HEX) and can have just as
   * many subfolders (I think :)
   * @param $id - User ID
   * @param $type - Image category
   * @return string
   */
  function calculateDirTree($id, $type)
  {
      $hashUserID   = substr(hash('md5', $id), -4);
      $parentFolder = substr($hashUserID,0,2);
      $subfolder    = substr($hashUserID,2);    
      $basePath     = $type."/".$parentFolder.'/'.$subfolder.'/';

      return $basePath;
  }  

Answer 1

Should images be stored in one folder, or many folders?

You are talking about "100k - 200k images" so many folders is a must have. Try to have max. ~1000 images in on folder.

Is it ok to use md5 for creating unique id's? E.g. md5(id+filename+random_num)

Yes, you can do this. It will avoid problems with long filenames.

Should images be cached on server or on clients browser / computer?

The should be cached on the client side. The problem with so many images is that it creates high traffic. Caching on the client help reducing this.

Answer 2

Depending on the number of images you want to handle, I would strongly suggest using several folders. The easiest way should be to use the first letter of the file name to create a folder structure. I think, the numbers are something like this:

less than 1000 images  --> one folder
less than 20000 images --> one level of folders (a, b, c, ...)
more                   --> several levels (a containing aa, ab, b containing ba, bb, ...)

YMMV