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From "James Dyer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-1787) Add ability to configure behavior of cache miss to CachedSqlEntityProcessor
Date Fri, 31 Aug 2012 14:55:07 GMT

    [ https://issues.apache.org/jira/browse/SOLR-1787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13446021#comment-13446021
] 

James Dyer commented on SOLR-1787:
----------------------------------

SOLR-2382 added support for pluggable cache implementations, which might be able to better
support Michael's 2 use-cases for this, making this feature less needed.  Also, the patch
is very much out of date and lacks unit tests.  Given an apparent lack of interest on this
one, I would make it "won't fix" unless anyone objects.
                
> Add ability to configure behavior of cache miss to CachedSqlEntityProcessor
> ---------------------------------------------------------------------------
>
>                 Key: SOLR-1787
>                 URL: https://issues.apache.org/jira/browse/SOLR-1787
>             Project: Solr
>          Issue Type: Improvement
>          Components: contrib - DataImportHandler
>    Affects Versions: 1.5
>         Environment: jdk 1.6.x, windows xp, tomcat 6.x
>            Reporter: Michael Henson
>            Assignee: Noble Paul
>            Priority: Minor
>              Labels: dih
>         Attachments: solr-1787.patch
>
>
> The CachedSqlEntityProcessor currently builds a cache of rows it sees as it goes, so
later requests for that same key can be served from data that has already been fetched. The
primary query could be written to fetch all possible rows, which would then be set into the
cache on the first request for a row. In that case the database would only receive another
query when there is a cache miss. However, the query it would execute is the one that pulls
all rows, negating any performance gain.
> This patch adds the ability to configure behavior on cache miss with the "onCacheMiss"
attribute on an "entity" tag in the data-config.xml file. The current behavior is the default,
corresponding to the setting onCacheMiss="fill". Any other value explicitly given for onCacheMiss
will cause cache misses to be ignored - no query will be made to the db to fulfill them.
> I've encountered two cases where this capability is useful:
> 1. Relatively small datasets, such as category id -> category name mappings, which
will not change during the course of indexing.
> 2. Queries which are heavy on db resources per-query, particularly if the query for an
individual record is slow, and can't be fixed easily on the db side for whatever reason.

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