Here's an in-depth article about the datastore that might interest you:

http://code.google.com/appengine/articles/storage_breakdown.html

On Wed, Dec 16, 2009 at 4:15 AM, Nick Johnson (Google) <
[email protected]> wrote:

> Hi bsb,
>
> - Each entity has a key that needs to be stored in various places. The key
> consists of your App ID, kind name, and name or ID, along with the usual
> Protocol Buffer overhead.
> - Each field is stored in the Protocol Buffer as a key, value pair. The
> total size for this is roughly len(key) + len(data) + 10 bytes (this last
> quantity can vary depending on the type and size of the property).
> - The automatic indexes also take up space. For each indexed field, they
> need roughly the length described above, plus the length of the App ID, plus
> the key for the entity. There are automatic indexes for single properties in
> ascending and descending order.
>
> Between the various fields that need to be stored and indexed, the size of
> an entity and all its indexes can easily reach 1KB, which fits your 1GB
> figure for a million of them.
>
> -Nick
>
> On Wed, Dec 16, 2009 at 11:53 AM, bsb <[email protected]> wrote:
>
>> I know this is an old story, but I still don't get it: I have ~1M
>> entities, each one consists of a date, a reference and 2 ints. I have
>> no custom indices or anything. The datastore statistics say that I'm
>> using 188MB for the entities. The quota view tells me I'm using a
>> whooping 1GB of disk space. How the *** does that work?
>>
>> --
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>>
>>
>
>
> --
> Nick Johnson, Developer Programs Engineer, App Engine
> Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number:
> 368047
>
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-- 
Ikai Lan
Developer Programs Engineer, Google App Engine

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