[storm] question on zstorm (aggressive caching)

[james at jamesh.id.au]

On Fri, Mar 11, 2011 at 6:51 AM, Roy Mathew <rmathew8 at gmail.com> wrote:
> Hi Gustavo, Thanks for your reply.
> My assumption was that the the goal of caching was to avoid making the
> same query more than once in a given transaction.
> However, my (perhaps flawed) analysis after a bit of digging suggests
> that this is not the case, and the caching model used in the storm
> container is more about managing objects in memory that correspond to
> table rows, and doing the right thing as far as their state is concerned
> when dirty, etc...
> Our application uses a SQL container model. I turned on logging on
> the postgres backend, and saw that doing something like this inside
> a transaction:
>   obj1 = C['key1']
>   obj1 = C['key1'] # and again
> (that is to say, it seems that invoking __getitem__ twice), causes the
> same SQL query to run twice. Please help me understand if I
> understand this correctly. thanks!

Storm's object cache works off of the table's primary key.  It doesn't
have any knowledge of any alternative keys for the table, so queries
that rely on those keys won't benefit from the cache.

As a general rule, calls to Store.get() (and code that calls it, such
as References to the primary key of a table) may avoid a query if
there is a cache hit, while calls to Store.find() will always issue a
query.

James.