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From "James Dyer (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-2382) DIH Cache Improvements
Date Thu, 13 Oct 2011 17:47:13 GMT

    [ https://issues.apache.org/jira/browse/SOLR-2382?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13126751#comment-13126751
] 

James Dyer commented on SOLR-2382:
----------------------------------

Pulkit,

I take it you have a root entity (possibly from a SQL database) and a child entity from a
flat text file, and you need to join the two data sources.  There are two ways to do this
using this caching.  In either case you'll need both patches ("entities" & "dihwriter").
 Also, if an in-memory cache is not adequate, you also need to get BerkleyBackedCache from
SOLR-2613 (required by the second 2-handler approach).  

The simple way uses a temporary (or ephemeral) cache.  To do this, create a single DIH Request
Handler and add your cached child entity to data-config.xml.  DIH will load and cache "child_entity"
every time you do an import.  When the import is finished, the cache is deleted.  This allows
you to do joins on flat files whereas without caching it would not be possible.  The downside
is if the flat file changes infrequently, or if you're doing delta updates on your index,
it would be inefficient to load and cache a large flat file every time.  Here's a sample data-config.xml:

{noformat}
<dataConfig>
 <dataSource name="SQL" ... />
 <dataSource name="URL" baseUrl="path_to_flat_file" type="URLDataSource" />
 <document name="my_doc">
   <entity name="root_entity" rootEntity="true" dataSource="SQL" pk="root_id" query="select
root_id, more_data, etc..." >
    <entity
     name="child_entity"
     processor="LineEntityProcessor"
     dataSource="URL"
     transformer="BreakIntoFieldsTransformerIWrote"
     cacheImpl="BerkleyBackedCache"
     cacheBaseDir="temp_location_for_cache"
     cachePk="root_id"
     cacheLookup="root_entity.root_id"
     fieldNames="root_id,  flatfiledata1, etc"
     fieldTypes="BIGDECIMAL, STRING, etc"
    />
   </entity>
 </document>
</dataConfig>
{noformat}

The second approach is to create a second DIH Request Handler in your solrconfig.xml for the
child entity.  This request handler has its own data-config.xml (named dih-flatfile.xml).
 You would run this second request handler to build a persistent cache for the flat file,
prior to running the main DIH request handler.  Here's an example of this second DIH Request
Handler configured in sorlconfig.xml:

{noformat}
<requestHandler name="/dih-flatfile" class="org.apache.solr.handler.dataimport.DataImportHandler">
 <lst name="defaults">
  <str name="config">dih-flatfile.xml</str>
  <str name="cacheDeletePriorData">true</str>
  <str name="fieldNames">root_id,  flatfiledata1, etc</str>
  <str name="fieldTypes">BIGDECIMAL, STRING, etc</str>
  <str name="writerImpl">org.apache.solr.handler.dataimport.DIHCacheWriter</str>
  <str name="cacheImpl">BerkleyBackedCache</str>
  <str name="cacheBaseDir">location_of_persistent_caches</str>
  <str name="cacheName">flatfile_cache_name</str>
  <str name="cachePk">root_id</str>
 </lst>
</requestHandler>
{noformat}

And here is what "dih-flatfile.xml" would look like:

{noformat}
<dataConfig>
 <dataSource name="URL" baseUrl="path_to_flat_file" type="URLDataSource" />
 <document name="my_doc_child">
   <entity name="child_entity" processor="LineEntityProcessor" dataSource="URL" transformer="BreakIntoFieldsTransformerIWrote"
/>
 </document>
</dataConfig>
{noformat}

Your main "dataconfig-xml" would look like this:

{noformat}
<dataConfig>
 <dataSource name="SQL" ... />
 <dataSource name="URL" baseUrl="path_to_flat_file" type="URLDataSource" />
 <document name="my_doc">
   <entity name="root_entity" rootEntity="true" dataSource="SQL" pk="root_id" query="select
root_id, more_data, etc..." >
    <entity
     name="child_entity"
     processor="org.apache.solr.handler.dataimport.DIHCacheProcessor"
     cacheImpl="BerkleyBackedCache"
     cachePk="root_id"
     cacheLookup="root_entity.root_id"
     cacheBaseDir="location_of_persistent_caches"
     cacheName="flatfile_cache_name"
    />
   </entity>
 </document>
</dataConfig>
{noformat}

This second approach offers more flexibility (you can load the persistent cache off-hours,
re-use it, do delta updates on it, etc) but it is significantly more complex.  The worst part
is to create a scheduler that will run the child entity's DIH request handler, wait until
it finishes, then run the main DIH Request handler.  But this is moot if you only need to
load the child once or once in a great while.

Should this all get committed, I will eventually create something on the wiki.  In the mean
time, I hope you find all of this helpful.  For more examples, see the xml files these patches
add to the "solr/contrib/dataimporthandler/src/test-files/dih/solr/conf" folder, and also
the new unit tests that use these.
                
> DIH Cache Improvements
> ----------------------
>
>                 Key: SOLR-2382
>                 URL: https://issues.apache.org/jira/browse/SOLR-2382
>             Project: Solr
>          Issue Type: New Feature
>          Components: contrib - DataImportHandler
>            Reporter: James Dyer
>            Priority: Minor
>         Attachments: SOLR-2382-dihwriter.patch, SOLR-2382-dihwriter.patch, SOLR-2382-entities.patch,
SOLR-2382-entities.patch, SOLR-2382-entities.patch, SOLR-2382-entities.patch, SOLR-2382-properties.patch,
SOLR-2382-properties.patch, SOLR-2382-solrwriter-verbose-fix.patch, SOLR-2382-solrwriter.patch,
SOLR-2382-solrwriter.patch, SOLR-2382-solrwriter.patch, SOLR-2382.patch, SOLR-2382.patch,
SOLR-2382.patch, SOLR-2382.patch, SOLR-2382.patch, SOLR-2382.patch, SOLR-2382.patch, SOLR-2382.patch
>
>
> Functionality:
>  1. Provide a pluggable caching framework for DIH so that users can choose a cache implementation
that best suits their data and application.
>  
>  2. Provide a means to temporarily cache a child Entity's data without needing to create
a special cached implementation of the Entity Processor (such as CachedSqlEntityProcessor).
>  
>  3. Provide a means to write the final (root entity) DIH output to a cache rather than
to Solr.  Then provide a way for a subsequent DIH call to use the cache as an Entity input.
 Also provide the ability to do delta updates on such persistent caches.
>  
>  4. Provide the ability to partition data across multiple caches that can then be fed
back into DIH and indexed either to varying Solr Shards, or to the same Core in parallel.
> Use Cases:
>  1. We needed a flexible & scalable way to temporarily cache child-entity data prior
to joining to parent entities.
>   - Using SqlEntityProcessor with Child Entities can cause an "n+1 select" problem.
>   - CachedSqlEntityProcessor only supports an in-memory HashMap as a Caching mechanism
and does not scale.
>   - There is no way to cache non-SQL inputs (ex: flat files, xml, etc).
>  
>  2. We needed the ability to gather data from long-running entities by a process that
runs separate from our main indexing process.
>   
>  3. We wanted the ability to do a delta import of only the entities that changed.
>   - Lucene/Solr requires entire documents to be re-indexed, even if only a few fields
changed.
>   - Our data comes from 50+ complex sql queries and/or flat files.
>   - We do not want to incur overhead re-gathering all of this data if only 1 entity's
data changed.
>   - Persistent DIH caches solve this problem.
>   
>  4. We want the ability to index several documents in parallel (using 1.4.1, which did
not have the "threads" parameter).
>  
>  5. In the future, we may need to use Shards, creating a need to easily partition our
source data into Shards.
> Implementation Details:
>  1. De-couple EntityProcessorBase from caching.  
>   - Created a new interface, DIHCache & two implementations:  
>     - SortedMapBackedCache - An in-memory cache, used as default with CachedSqlEntityProcessor
(now deprecated).
>     - BerkleyBackedCache - A disk-backed cache, dependent on bdb-je, tested with je-4.1.6.jar
>        - NOTE: the existing Lucene Contrib "db" project uses je-3.3.93.jar.  I believe
this may be incompatible due to Generic Usage.
>        - NOTE: I did not modify the ant script to automatically get this jar, so to use
or evaluate this patch, download bdb-je from http://www.oracle.com/technetwork/database/berkeleydb/downloads/index.html

>  
>  2. Allow Entity Processors to take a "cacheImpl" parameter to cause the entity data
to be cached (see EntityProcessorBase & DIHCacheProperties).
>  
>  3. Partially De-couple SolrWriter from DocBuilder
>   - Created a new interface DIHWriter, & two implementations:
>    - SolrWriter (refactored)
>    - DIHCacheWriter (allows DIH to write ultimately to a Cache).
>    
>  4. Create a new Entity Processor, DIHCacheProcessor, which reads a persistent Cache
as DIH Entity Input.
>  
>  5. Support a "partition" parameter with both DIHCacheWriter and DIHCacheProcessor to
allow for easy partitioning of source entity data.
>  
>  6. Change the semantics of entity.destroy()
>   - Previously, it was being called on each iteration of DocBuilder.buildDocument().
>   - Now it is does one-time cleanup tasks (like closing or deleting a disk-backed cache)
once the entity processor is completed.
>   - The only out-of-the-box entity processor that previously implemented destroy() was
LineEntitiyProcessor, so this is not a very invasive change.
> General Notes:
> We are near completion in converting our search functionality from a legacy search engine
to Solr.  However, I found that DIH did not support caching to the level of our prior product's
data import utility.  In order to get our data into Solr, I created these caching enhancements.
 Because I believe this has broad application, and because we would like this feature to be
supported by the Community, I have front-ported this, enhanced, to Trunk.  I have also added
unit tests and verified that all existing test cases pass.  I believe this patch maintains
backwards-compatibility and would be a welcome addition to a future version of Solr.

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