[ZODB-Dev] Re: [Zope3-dev] Re: Community opinion about search+filter
faassen at startifact.com
Sun Mar 25 12:33:18 EDT 2007
Jim Fulton wrote:
> On Mar 25, 2007, at 3:01 AM, Adam Groszer wrote:
>> MF> I think one of the main limitations of the current catalog (and
>> MF> hurry.query) is efficient support for sorting and batching the query
>> MF> results. The Zope 3 catalog returns all matching results, which
>> can then
>> MF> be sorted and batched. This will stop being scalable for large
>> MF> collections. A relational database is able to do this internally,
>> and is
>> MF> potentially able to use optimizations there.
> What evidence to you have to support this assertion?
I have the strong suspicion that modern relational databases are
currently better able to scale at queries using LIMIT and ORDER BY than
the Zope 3 catalog. I cannot back this up as I haven't done
measurements. Perhaps you have done so?
* Do you estimate the performance of the Zope 3 catalog to be equivalent
to the performance of a modern relational database system for queries
that need to sort and batch their results?
* If so, do you think it's just as easy for a developer to accomplish
such equivalent performance with the Zope 3 catalog as it is with a
I've made a number of assertions:
a) one of the main limitations of the current catalog and hurry.query is
efficient support for sorting and batching.
b) the Zope 3 catalog returns all matching results, which can then be
sorted and batched. This will stop being scalable for large collections.
I'll amend b) by saying 'This will stop being scalable for large result
sets'. I agree that b) as stated above is incorrect as the result set
might be small, but I intended the amendment.
c) A relational database is able to do sorting and batching (limit
queries) internally, and is potentially able to use optimizations here.
Which of these assertions are false?
Don't you think relational database system that has support for sorting
and batching built into its query API can at the very least more easily
use approaches to reduce sorting cost, by rewriting the query, caching,
and potentially employing special indexes?
> We did some
> literature search on this a few years ago and found no special trick to
> avoid sorting costs.
I am at least cursorily aware of challenges surrounding efficient
querying and batching. I am not looking for a special trick or magic
bullet. I'd just like more help in avoiding sorting cost in a typical
situation where results are displayed in a batched format.
If a catalog query returns 1 million results, which I want to show in
batches of 10, sorted by some property of the results, I would like to
reduce the costs. Currently the pattern I (and I imagine others) employ
is to re-execute the query and then sort these results in memory for
each batch, for each request.
[you list some approaches to reduce sorting cost]
I would like some system that helps me reduce some of these costs, using
the approaches you list, or at least some caching somewhere. I would
imagine a relational database for instance can employ caching of result
sets, so that if no writes occurred, a second LIMIT query asking for a
different range will return results a lot faster.
Apparently the catalog does support N-best, you state later in this
thread. How does one use this support? Can I add it to hurry.query somehow?
Perhaps all this is not the reponsibility of the catalog itself, but a
system surrounding it. As long as it's obviously there for people to use.
Perhaps however I am seeing problems that aren't there?
Do you think there is no problem and we have parity with relational
database implementations here?
Do you think the current situation cannot be improved much further?
Do you think any further improvements are not worth the costs?
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