On Oct 4, 2006, at 12:56 PM, Guy Rouillier wrote:

TIJod wrote:
I need to store a large number of images in a
PostgreSQL database. In my application, this
represents a few hundreds of thousands of images. The
size of each image is about 100-200 Ko. There is a
large turnover in my database, i.e. each image stays
about 1 week in the database, then it is deleted.

I see little value to storing the images in the database. For me that's
a general statement (I'm sure others will disagree); but especially in
your case, where you have a high volume and only want to store them for
a couple days.  Why incur all the overhead of putting them in the DB?
You can't search on them or sort on them.  I would just store them in
the file system and put a reference in the DB.

but this wouldrequire a more tricky implementation, and ACID-ity
would be difficult to ensure -- after all, a database
should abstract the internal storage of data, may it
be images).

I can't get excited about this.  First, given the amount of overhead
you'll be avoiding, checking the return code from storing the image in
the file system seems relatively trivial. Store the image first, and if
you get a failure code, don't store the rest of the data in the DB;
you've just implemented data consistency. That assumes, of course, that the image is the only meaningful data you have, which in most situations
is not the case.  Meaning you'd want to store the rest of the data
anyway with a messages saying "image not available."

Combine that with an on delete trigger that adds the filename
to a deletion queue (within the transaction) and a separate
process that runs through the deletion queue occasionally
and you get something quite useable, while still being able
to use sendfile() to throw the image over the wire rather than
squeezing all that data through the database.

Cheers,
  Steve


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