On Apr 14, 2011, at 5:07 PM, Chung wrote:
> Thanks Michael! Re: the heavy get() workload, that's a neat trick :-)
> Unfortunately for our workload, we don't really know which set of gets() are
> going to fire, and we can't fit the entire table into memory.
>
>
>
>
> I was curious about whether passing in fields instead of tables into Query
> and getting NamedTuples back would be more efficient. I ran some (not too
> rigorous) benchmarks to perform 3000 "gets" to retrieve all columns. The
> table has 77 columns. I'm using 0.6.6. Results:
> Fetch by table instance -- ~25 seconds
> Fetch by all table columns (returning NamedTuples) -- ~27 seconds
> Fetch with cached compiled statements -- ~11 seconds
> Fetch with cached compiled statements + "faster" populate_instance -- ~6
> seconds
> Fetch with cached compiled statements + "faster" populate_instance + cached
> ResultMetaData -- ~3.4 seconds
> So I imagine that getting NamedTuples back is really only cheaper if we also
> select fewer columns (which we don't want to do at the moment).
>
> The BakedQuery recipe is interesting, though it'd require us to go through
> the same Query instance whenever we want to issue a similar query. For us,
> we've created a TextualQuery which allows something like this:
>
> session.query(Table).textual('where id=:id and createddate > :createddate',
> id=id, createddate=date)
>
> The textual() method essentially turns the query into a Query.from_statement
> query, and we use a session-wide cache for mapping textual query strings to
> statement instances, as well as a session-wide compiled_cache. The reason
> why we used query strings is just that we need to make sure we use the same
> statement instance for the same query, and we feel safer comparing these
> strings than figuring out when two Query objects are equivalent :-)
well that recipe is a scratch idea - i think you could likely adapt it so that
bake() or whatever is passed a string that pulls up something that's cached
(like even the Query object itself that's baked). I want to try to have it
cache the whole QueryContext, or some section of it, as well.
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