[hibernate-dev] Should we deprecate @Similarity

Sanne Grinovero sanne at hibernate.org
Mon Sep 23 06:28:33 EDT 2013

Planned for 4.4:

On 19 September 2013 16:55, Hardy Ferentschik <hardy at hibernate.org> wrote:
> On 19 Jan 2013, at 5:15 PM, Sanne Grinovero <sanne at hibernate.org> wrote:
>> Discussing about some hibernate-search-engine complexities with Hardy
>> on IRC, we came to the agreement that the way @Similarity behaves
>> today was a mistake, so we're proposing to deprecate it in 4.4.
>> Reasoning follows.
>> There is a strong requirement in Lucene that all operations on the
>> same index need to use the same Similarity implementation. We infer
>> the org.apache.lucene.search.Similarity to be used on a specific index
>> from either:
>> - the similarity property from the configuration file, which is
>> positioned on an index name
>> - the @Similarity annotation positioned on an indexed entity
>> The trouble is about all these options needing to be consistent; first
>> problem is there isn't a precedence rule: if one of them is not
>> specified, we assume the user is using the other way to configure
>> things. But also different entities might be sharing the same index,
>> which leads to needing to verify that at least the user isn't
>> specifying some contradictory option.
>> This all gets more confusing when you introduce the notion of
>> dynamically added new entities (a feature used by Infinispan) and/or
>> Dynamic Sharding, in which the properties of some indexes might
>> conflict with the specified @Similarity, but we might notice this only
>> at runtime rather than at bootstrap. Failing to load a class at this
>> point is far more annoying to the users than to fail the health-check
>> at bootstrap time.
>> So the proposal:
>> drop the @Similarity annotation and use properties exclusively.
>> Properties are more suited for this as they are set on a per-index
>> base, which is what matters in this case.
>> Downside:
>> I guess lots of people where using a single index per type, and for
>> those there was no danger to simply specify a @Similarity. We lose
>> this straight-forward way of things, but I'd argue that if you're in
>> the business of specifying a custom Similarity, you're a very advanced
>> user and wouldn't mind setting a one-liner in your configuration file.
>> Do we agree?
> +1 to all your points
> --Hardy
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