Hey Alex,
As described in the other thread, the cost of maintaining indexes matters
here, and there are other restrictions described in the documentation
<https://cloud.google.com/appengine/docs/java/datastore/projectionqueries#Java_Limitations_on_projections>.
I
hope this helps clarify the trade-offs for you.
Regards,
Nick
Cloud Platform Community Support
On Thursday, April 7, 2016 at 9:16:57 AM UTC-4, Alex Kerr wrote:
>
> Thanks Nick. So can you confirm costs are:
>
> 1.) For a projection query, cost is a single read for the entire query
> regardless of number of results returned (and same under the new Datastore
> pricing)
> 2.) For a projection query with distinct option, cost is 1 read + 1 read
> per entity retrieved
> 3.) For normal queries ("SELECT * FROM ... " in GQL) under the new (from
> July) Datastore pricing, cost is 1 read per entity
>
> Are there drawbacks to the suggestion made by the poster of that link you
> specified, in achieving a "SELECT * " at projection query cost, by adding
> in a dummy property to the entity kind and then doing a projection query on
> the remaining properties? (I suppose the obvious drawback being you'd need
> an index for every property)
>
> Thanks,
> Alex
>
>
> On Thursday, April 7, 2016 at 12:31:22 AM UTC+1, Nick (Cloud Platform
> Support) wrote:
>>
>> Hi Alex,
>>
>> I believe this old App Engine Groups thread
>> <https://groups.google.com/forum/#!msg/google-appengine/iL9ci30WSxU/0vLuvv8fAwAJ>
>>
>> answers your question adequately. Let me know if you have any questions
>> after reading.
>>
>> Cheers,
>>
>> Nick
>> Cloud Platform Community Support
>>
>> On Wednesday, April 6, 2016 at 10:12:15 AM UTC-4, Alex Kerr wrote:
>>>
>>> Hi,
>>>
>>> Can anyone clarify the cost of projection queries please? (both in
>>> operations and financially)
>>>
>>> Datastore pricing page at:
>>> https://cloud.google.com/datastore/docs/pricing says a regular query
>>> (is that "SELECT * " ?) is 1 read + 1 read per entity retrieved. I get
>>> that, but then projection queries are just "1 read" - which implies a cost
>>> of 1 read total regardless of the number of results returned and the number
>>> of properties projected - that can't be right?
>>>
>>> Also I note the new pricing section from July but still not clear on
>>> projection query cost!
>>>
>>> Many thanks
>>> Alex
>>>
>>
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