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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-8621) solrconfig.xml: deprecate/replace <mergePolicy> with <mergePolicyFactory>
Date Sat, 06 Feb 2016 15:44:39 GMT

    [ https://issues.apache.org/jira/browse/SOLR-8621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15135830#comment-15135830
] 

Shai Erera commented on SOLR-8621:
----------------------------------

[~cpoerschke] I reviewed the latest patch and here's my take on {{SimpleMergePolicyFactory}}:
at first, I thought about this approach too, but eventually preferred the explicit {{TieredMPFactory}}.
It has few advantages IMO:

* It's simple. Requires less typing by the user, and having a SimpleMPF for which you declare
a 'class' feels like a level of indirection. It's as if SimpleMPF itself has no use.
* WrapperMPF is also a code-only class, but users don't specify it explicitly in config.xml.
Users would specify a SortingMPF or UpgradeIndexMPF.
* The 'class' element of WrapperMPF is a Factory class, not an MP class. Unlike the one we'll
have on SimpleMPF.

If we'll have both SimpleMPF and TieredMPF, it feels like duplicated efforts. Perhaps we should
start simple (i.e. keep SimpleMPF abstract and only expose the concrete factories) and if
demand arises, we can make it a concrete class too? That route is always back-compat, but
the other one may not be.

So Simple/Wrapper belong more to the code-design land, while the concrete factories belong
to the user land.

What do you think?

> solrconfig.xml: deprecate/replace <mergePolicy> with <mergePolicyFactory>
> -------------------------------------------------------------------------
>
>                 Key: SOLR-8621
>                 URL: https://issues.apache.org/jira/browse/SOLR-8621
>             Project: Solr
>          Issue Type: Task
>            Reporter: Christine Poerschke
>            Assignee: Christine Poerschke
>
> *<mergePolicyFactory> end-user benefits:*
> * Lucene's UpgradeIndexMergePolicy can be configured in Solr
> * (with SOLR-5730) Lucene's SortingMergePolicy can be configured in Solr
> * customisability: arbitrary merge policies including wrapping/nested merge policies
can be created and configured
> *(proposed) roadmap:*
> * solr 5.5 introduces <mergePolicyFactory> support
> * solr 5.5(\?) deprecates (but maintains) <mergePolicy> support
> * solr 6.0(\?) removes <mergePolicy> support 
> +work-in-progress git branch:+ [master-solr-8621|https://github.com/apache/lucene-solr/tree/master-solr-8621]



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