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collective.solr 2.0

Solr integration for external indexing and searching.

Latest Version: 4.0

Introduction

collective.solr integrates the Solr search engine with Plone.

Apache Solr is based on Lucene and is the enterprise open source search engine. It powers the search of sites like Twitter, the Apple and iTunes Stores, Wikipedia, Netflix and many more.

Solr does not only scale to any level of content, but provides rich search functionality, like facetting, geospatial search, suggestions, spelling corrections, indexing of binary formats and a whole variety of powerful tools to configure custom search solutions. It has integrated clustering and load-balancing to provide a high level of robustness.

collective.solr comes with a default configuration and setup of Solr that makes it extremely easy to get started, yet provides a vastly superior search quality compared to Plone's integrated text search based on ZCTextIndex.

Current Status

The code is used in production in many sites and considered stable. This add-on can be installed in a Plone 4.x site to enable indexing operations as well as searching (site and live search) using Solr. Doing so will not only significantly improve search quality and performance - especially for a large number of indexed objects, but also reduce the memory footprint of your Plone instance by allowing you to remove the SearchableText, Description and Title indexes from the catalog. In large sites with 100000 content objects and more, searches using ZCTextIndex often taken 10 seconds or more and require a good deal of memory from ZODB caches. Solr will typically answer these requests in 10ms to 50ms at which point network latency and the rendering speed of Plone's page templates are a more dominant factor.

Installation

The following buildout configuration may be used to get started quickly:

[buildout]
extends =
  buildout.cfg
  https://raw.github.com/Jarn/collective.solr/2.0/buildout/solr.cfg

[instance]
eggs += collective.solr

After saving this to let's say solr.cfg the buildout can be run and the Solr server and Plone instance started:

$ python bootstrap.py
$ bin/buildout -c solr.cfg
...
$ bin/solr-instance start
$ bin/instance start

Next you should activate the collective.solr (site search) add-on in the add-on control panel of Plone. After activation you should review the settings in the new Solr Settings control panel. To index all your content in Solr you can call the provided maintenance view:

http://localhost:8080/plone/@@solr-maintenance/reindex

Note that the example solr.cfg is bound to change. Always copy the file to your local buildout. In general you should never rely on extending buildout config files from servers that aren't under your control.

Architecture

When working with Solr it's good to keep some things about it in mind. This information is targeted at developers and integrators trying to use and extend Solr in their Plone projects.

Indexing

Solr is not transactional aware or supports any kind of rollback or undo. We therefor only sent data to Solr at the end of any successful request. This is done via collective.indexing, a transaction manager and a end request transaction hook. This means you won't see any changes done to content inside a request when doing Solr searches later on in the same request. Inside tests you need to either commit real transactions or otherwise flush the Solr connection. There's no transaction concept, so one request doing a search might get some results in its beginning, than a different request might add new information to Solr. If the first request is still running and does the same search again it might get different results taking the changes from the second request into account.

Solr is not a real time search engine. While there's work under way to make Solr capable of delivering real time results, there's currently always a certain delay up to some minutes from the time data is sent to Solr to when it is available in searches.

Search results are returned in Solr by distinct search threads. These search threads hold a great number of caches which are crucial for Solr to perform. When index or unindex operations are sent to Solr, it will keep those in memory until a commit is executed on its own search index. When a commit occurs, all search threads and thus all caches are thrown away and new threads are created reflecting the data after the commit. While there's a certain amount of cache data that is copied to the new search threads, this data has to be validated against the new index which takes some time. The useColdSearcher and maxWarmingSearchers options of the Solr recipe relate to the aspect. While cache data is copied over and validated for a new search thread, it's warming up. If that process is not yet completed the thread is considered to be cold.

In order to get real good performance out of Solr, we need to minimize the number of commits against the Solr index. We can achieve this by turning off auto-commit and instead use commitWithin. So we don't sent a commit to Solr at the end of each index/unindex request on the Plone side. Instead we tell Solr to commit the data to its index at most after a certain time interval. Values of 15 minutes to 1 minute work well for this interval. The larger you can make this interval, the better the performance of Solr will be, at the cost of search results lagging behind a bit. In this setup we also need to configure the autoCommitMaxTime option of the Solr server, as commitWithin only works for index but not unindex operations. Otherwise a large number of unindex operations without any index operations occurring could not be reflected in the index for a long time.

As a result of all the above, the Solr index and the Plone site will always have slightly diverging contents. If you use Solr to do searches you need to be aware of this, as you might get results for objects that no longer exist. So any brain/getObject call on the Plone side needs to have error handling code around it as the object might not be there anymore and traversing to it throws an exception.

When adding new or deleting old content or changing the workflow state of it, you will also not see those actions reflected in searches right away, but only after a delay of at most the commitWithin interval. After a commitWithin operation is sent to Solr, any other operations happening during that time window will be executed after the first interval is over. So with a 15 minute interval, if document A is indexed at 5:15, B at 5:20 and C at 5:35, both A & B will be committed at 5:30 and C at 5:50.

Searching

Information retrieval is a complex science. We try to give a very brief explanation here, refer to the literature and documentation of Lucene/Solr for much more detailed information.

If you do searches in normal Plone, you have a search term and query the SearchableText index with it. The SearchableText is a simple concentration of all searchable fields, by default title, description and the body text.

The default ZCTextIndex in Plone uses a simplified version of the Okapi BM25 algorithm described in papers in 1998. It uses two metrics to score documents:

  • Term frequency: How often does a search term occur in a document
  • Inverse document frequency: The inverse of in how many documents a term occurs. Terms only occurring in a few documents are scored higher than those occurring in many documents.

It calculates the sum of all scores, for every term common to the query and any document. So for a query with two terms, a document is likely to score higher if it contains both terms, except if one of them is a very common term and the other document contains the non-common term more often.

The similarity function used in Solr/Lucene uses a different algorithm, based on a combination of a boolean and vector space model, but taking the same underlying metrics into account. In addition to the term frequency and inverse document frequency Solr respects some more metrics:

  • length normalization: The number of all terms in a field. Shorter fields contribute higher scores compared to long fields.
  • boost values: There's a variety of boost values that can be applied, both index-time document boost values as well as boost values per search field or search term

In its pre 2.0 versions, collective.solr used a naive approach and mirrored the approach taken by ZCTextIndex. So it sent each search query as one query and matched it against the full SearchableText field inside Solr. By doing that Solr basically used the same algorithm as ZCTextIndex as it only had one field to match with the entire text in it. The only difference was the use of the length normalization, so shorter documents ranked higher than those with longer texts. This actually caused search quality to be worse, as you'd frequently find folders, links or otherwise rather empty documents. The Okapi BM25 implementation in ZCTextIndex deliberately ignores the document length for that reason.

In order to get good or better search quality from Solr, we have to query it in a different way. Instead of concatenating all fields into one big text, we need to preserve the individual fields and use their intrinsic importance. We get the main benefit be realizing that matches on the title and description are more important than matches on the body text or other fields in a document. collective.solr 2.0+ does exactly that by introducing a search-pattern to be used for text searches. In its default form it causes each query to work against the title, description and full searchable text fields and boosts the title by a high and the description by a medium value. The length normalization already provides an improvement for these fields, as the title is likely short, the description a bit longer and the full text even longer. By using explicit boost values the effect gets to be more pronounced.

If you do custom searches or want to include more fields into the full text search you need to keep the above in mind. Simply setting the searchable attribute on the schema of a field to True will only include it in the big searchable text stream. If you for example include a field containing tags, the simple tag names will likely 'drown' in the full body text. You might want to instead change the search pattern to include the field and potentially put a boost value on it - though it will be more important as it's likely to be extremely short. Similarly extracting the full text of binary files and simply appending them into the search stream might not be the best approach. You should rather index those in a separate field and then maybe use a boost value of less than one to make the field less important. Given to documents with the same content, one as a normal page and one as a binary file, you'll likely want to find the page first, as it's faster to access and read than the file.

There's a good number of other improvements you can do using query time and index time boost values. To provide index time boost values, you can provide a skin script called solr_boost_index_values which gets the object to be indexed and the data sent to Solr as arguments and returns a dictionary of field names to boost values for each document. The safest is to return a boost value for the empty string, which results in a document boost value. Field level boost values don't work with all searches, especially wildcard searches as done by most simple web searches. The index time boost allows you to implement policies like boosting certain content types over others, taking into account ratings or number of comments as a measure of user feedback or anything else that can be derived from each content item.

Development

Releases can be found on the Python Package Index at http://pypi.python.org/pypi/collective.solr. The code and issue trackers can be found on GitHub at https://github.com/Jarn/collective.solr.

For outstanding issues and features remaining to be implemented please see the to-do list included in the package as well as it's issue tracker.

Credits

This code was inspired by enfold.solr by Enfold Systems as well as work done at the snowsprint'08. The solr.py module is based on the original python integration package from Solr itself.

Development was kindly sponsored by Elkjop and the Nordic Council and Nordic Council of Ministers.

Changelog

2.0 - 2011-06-04

  • Updated readme and project description, adding detailed information about how Solr works and how we integrate with it. [hannosch]

2.0b2 - 2011-05-18

  • Added optional support for the Lazy backports founds in catalogqueryplan. [hannosch]
  • Fixed patch of LazyCat's __add__ method to patch the base class instead, as the method was moved. [hannosch]
  • Updated test config to Solr 3.1, which should be supported but hasn't seen extensive production use. [hannosch]
  • Avoid using the deprecated five:implements directive. [hannosch]

2.0b1 - 2011-04-06

  • Rewrite the isSimpleSearch function to use a less complex regular expression, which doesn't have O(2**n) scaling properties. [hannosch]
  • Use the standard libraries doctest module. [hannosch]
  • Fix the pretty_title_or_id method from PloneFlare; the implementation was broken, now delegates to the standard Plone implementation. [mj]

2.0a3 - 2011-01-26

  • In solr_dump_catalog correctly handle boolean values and empty text fields. [hannosch]

2.0a2 - 2011-01-10

  • Provide a dummy request in the solr_dump_catalog command. [hannosch]

2.0a1 - 2011-01-10

  • Handle utf-8 encoded data correctly in utils.isWildCard. [hannosch]
  • Gracefully handle exceptions raised during index data retrieval. [tom_gross, hannosch]
  • Added zopectl.command entry points for three new scripts. solr_clear_index will remove all entries from Solr. solr_dump_catalog will efficiently dump the content of the catalog onto the filesystem and solr_import_dump will import the dump into Solr. This can be used to bootstrap an empty Solr index or update it when the boost logic has changed. All scripts will either take the first Plone site found in the database or accept an unnamed command line argument to specify the id. The Solr server needs to be running and the connection info needs to be configured in the Plone site. Example use: bin/instance solr_dump_catalog Plone. In this example the data would be stored in var/instance/solr_dump_plone. The data can be transferred between machines and calling solr_dump_catalog multiple times will append new data to the existing dump. To get Solr up-to-date you should still call @@solr-maintenance/sync. [hannosch, witsch]
  • Changed search pattern syntax to use str.format syntax and make both {value} and {base_value} available in the pattern. [hannosch]
  • Add possibility to calculate site-specific boost values via a skin script. [hannosch, witsch]
  • Fix wildcard searches for patterns other than just ending with an asterisk. [hannosch, witsch]
  • Require Plone 4.x, declare package dependencies & remove BBB bits. [hannosch, witsch]
  • Add configurable setting for custom search pattern for simple searches, allowing to include multiple fields with specific boost values. [hannosch, witsch]
  • Don't modify search parameters during indexing. [hannosch, witsch]
  • Fixed auto-commit support to actually sent the data to Solr, but omit the commit message. [hannosch]
  • Added support for commitWithin support on add messages as per SOLR-793. This feature requires a Solr 1.4 server. [hannosch]
  • Split out 404 auto-suggestion tests into a separate file and disabled them under Plone 4 - the feature is no longer part of Plone. [hannosch]
  • Fixed error handling code to deal with different exception string representations in Python 2.6. [hannosch]
  • Made tests independent of the Large Folder content type, as it no longer exists in Plone 4. [hannosch]
  • Avoid using the incompatible TestRequest from zope.publisher inside Zope 2. [hannosch]
  • Fixed undefined variables in search.pt for Plone 4 compatibility. [hannosch]

1.1 - Released March 17, 2011

  • Still index, if a field can't be accessed. [tom_gross]
  • Fix the pretty_title_or_id method from PloneFlare; the implementation was broken, now delegates to the standard Plone implementation. [mj]

1.0 - Released September 14, 2010

  • Enable multi-field "fq" statements. [tesdal, witsch]
  • Prevent logging of "unknown" search attributes for use_solr and the infamous -C Zope startup parameter. [witsch]

1.0rc3 - Released September 9, 2010

  • Add logging of queries without explicit "rows" parameter. [witsch]
  • Add configuration to exclude user from allowedRolesAndUsers for better cacheability. [tesdal, witsch]
  • Add configuration for effective date steps. [tesdal, witsch]
  • Handle python datetime and date objects. [do3cc, witsch]
  • Fixed a grammar error in error.pt. [hannosch]

1.0rc2 - Released August 31, 2010

  • Fix regression about catalog fallback with required, but empty parameters. [tesdal, witsch]

1.0rc1 - Released July 30, 2010

1.0b24 - Released July 29, 2010

  • Fix security issue with getObject on Solr flares, which used unrestricted traversal on the entire path, potentially leading to information leaks. Refs http://plone.org/products/collective.solr/issues/27 [pilz, witsch]
  • Add missing CreationDate method to flares. This fixes http://plone.org/products/collective.solr/issues/16 [witsch]
  • Add logging for slow queries along with the query time as reported by Solr. [witsch]
  • Limit number of matches looked up during live search for speedier replies. [witsch]
  • Renamed the batch parameters to b_start and b_size to avoid conflicts with index names and be consistent with existing template code. [do3cc]
  • Added a new config option auto-commit which is enabled by default. You can disable this, which avoids any explicit commit messages to be sent to the Solr server by the client. You have to configure commit policies on the server side instead. [hannosch]
  • Added support for a special query key use_solr which forces queries to be sent to Solr even though none of the required keys match. This can be used to sent individual catalog queries to Solr. [hannosch]

1.0b23 - Released May 15, 2010

  • Add support for batching, i.e. only fetch and parse items from Solr, which are part of the currently handled batch. [witsch]
  • Fix quoting of operators for multi-word search terms. [witsch]
  • Use the faster C implementations of elementtree/xml.etree if available. [hannosch, witsch]
  • Grant restricted code access to the search results, e.g. skin scripts. [do3cc, witsch]
  • Fix handling of 'depth' argument when querying multiple paths. [reinhardt, witsch]
  • Don't break when filter queries should be used for all parameters. [reinhardt, witsch]
  • Always provide values for all metadata columns like the catalog does. [witsch]
  • Always fall back to portal catalog for "navtree" queries so the set of required query parameters can be empty. This refs http://plone.org/products/collective.solr/issues/18 [reinhardt, witsch]
  • Prevent parsing errors for dates from before 1000 A.D. in combination with 32-bit systems and Solr 1.4. [reinhardt, witsch]
  • Don't process content with its own indexing methods, e.g. reindexObject, via the reindex maintenance view. [witsch]
  • Let query builder handle sets of possible boolean values as passed by boolean topic criteria for example. [hannosch, witsch]
  • Recognize new solr.TrieDateField field type and handle it in the same way as we handle the older solr.DateField. [hannosch]
  • Warn about missing search indices and non-stored sort parameters. [witsch]
  • Fix issue when reindexing objects with empty date fields. [witsch]
  • Changed the default schema for is_folderish to store the value. The reference browser search expects it on the brain. [hannosch]
  • Changed the GenericSetup export/import handler for the Solr manager to ignore non-persistent utilities. [hannosch]
  • Add support for LinguaPlone. [witsch]
  • Update sample Solr buildout configuration and documentation to recommend a high enough default setting for maximum search results returned by Solr. This refs http://plone.org/products/collective.solr/issues/20 [witsch]

1.0b22 - Released February 23, 2010

  • Split out a BaseSolrConnectionConfig class, to be used for registering a non-persistent connection configuration. [hannosch]
  • Fix bug regarding timeout locking. [witsch]
  • Convert test setup to collective.testcaselayer. [witsch]
  • Only apply timeout decorator when actually committing changes to Solr, also re-enabling the use of query parameters for maintenance views again. [witsch]
  • We also need to change the SearchDispatcher to use the original method in case Solr isn't active. [hannosch]
  • Changed the searchResults monkey to store and use the method found on the class instead of assuming it comes from the base class. This makes things work with LinguaPlone which also patches this method. [hannosch]
  • Add dutch translation. [WouterVH]
  • Refactor buildout to allow running tests against Plone 4.x. [witsch]
  • Optimize reindex behavior when populating the Solr index for the first time. [hannosch, witsch]
  • Only register indexable attributes the old way on Plone 3.x. [jcbrand]
  • Fix timeout decorator to work ttw. [hannosch, witsch]
  • Add "z3c.autoinclude.plugin" entry point, so in Plone 3.3+ you can avoid loading the ZCML file. [hannosch]

1.0b21 - Released February 11, 2010

  • Fix unindexing to not fetch more data from the objects than necessary. [witsch]
  • Use decorator to lock timeouts and make sure the lock is always released. [witsch]
  • Fix maintenance views to work without setting up a Solr connection first. [witsch]

1.0b20 - Released January 26, 2010

  • Fix reindexing to always provide data for all fields defined in the schema as support for "updateable/modifiable documents" is only planned for Solr 1.5. See https://issues.apache.org/jira/browse/SOLR-139 for more info. [witsch]
  • Fix CSS issues regarding facet display on IE6. [witsch]

1.0b19 - Released January 24, 2010

  • Fix partial reindexing to preserve data for indices that are not stored. [witsch]
  • Help with improved logging of auto-flushes for easier performance tuning. [witsch]

1.0b18 - Released January 23, 2010

  • Work around layout issue regarding facet counts on IE6. [witsch]

1.0b17 - Released January 21, 2010

  • Don't confuse pre-configured filter queries with facet selections. [witsch]
  • Always display selected facets, even, or especially, without search results. [witsch]

1.0b16 - Released January 11, 2010

  • Remove catalogSync maintenance view since it would need to fetch additional data (for non-stored indices) from the objects themselves in order to work correctly. [witsch]
  • Fix reindex maintenance view to preserve data that cannot be fetched from Solr during partial indexing, i.e. indices that are not stored. [witsch]
  • Use wildcard searches for simple search terms to reflect Plone's default behaviour. [witsch]
  • Fix drill-down for facet values containing white space. [witsch]
  • Add support for partial syncing of catalog and solr indexes. [witsch]

1.0b15 - Released October 12, 2009

1.0b14 - Released September 17, 2009

  • Fix query builder to use explicit ORs so that it becomes possible to change Solr's default operator to AND. [witsch]
  • Remove relevance information from search results as they don't make sense to the user. [witsch]

1.0b13 - Released August 20, 2009

  • Fix reindex and catalogSync maintenance views to not pass invalid data back to Solr when indexing an explicit list of attributes. [witsch]

1.0b12 - Released August 15, 2009

  • Fix reindex maintenance view to keep any existing data when indexing a given list of attributes. [witsch]
  • Add support for facet dependencies: Specifying a facet "foo" like "foo:bar" only makes it show up when a value for "bar" has been previously selected. [witsch]
  • Allow indexer methods to raise AttributeError to prevent an attribute from being indexed. [witsch]

1.0b11 - Released July 2, 2009

  • Fix maintenance view for adding/syncing single indexes using catalog data. [witsch]
  • Allow to configure query parameters for which filter queries should be used (see http://wiki.apache.org/solr/FilterQueryGuidance for more info) [fschulze, witsch]
  • Encode unicode strings when building facet links. [fschulze, witsch]
  • Fix facet display to try to keep the given order of facets. [witsch]
  • Allow facet values to be translated. [witsch]

1.0b10 - Released June 11, 2009

  • Range queries must not be quoted with the new query parser. [witsch]
  • Disable socket timeouts during maintenance tasks. [witsch]
  • Close the response object after searching in order to avoid ResponseNotReady errors triggering duplicate queries. [witsch]
  • Use proper way of accessing jQuery & fix IE6 syntax error. [fschulze]
  • Format relevance value for search results. [witsch]

1.0b9 - Released May 12, 2009

1.0b8 - Released May 4, 2009

1.0b7 - Released April 28, 2009

  • Fix unintended (de)activation of the Solr integration during profile (re)application. [witsch]
  • Fix display of facet information with no active facets. [witsch]
  • Register import and export steps using ZCML. [witsch]

1.0b6 - Released April 20, 2009

  • Add support for facetted searches. [witsch]
  • Update code to comply to PEP8 style guide lines. [witsch]
  • Expose additional information provided by Solr - for example about headers and search facets. [witsch]
  • Handle edge cases like invalid range queries by quoting [tesdal]
  • Parse and quote the query to filter invalid query syntax. [tesdal]
  • In solrSearchResults, if the passed in request is a dict, look up request to enable adaptation into PloneFlare. [tesdal]
  • Added support for objects with a 'query' attribute as search values. [tmog]

1.0b5 - Released December 16, 2008

  • Fix and extend logging in "sync" maintenance view. [witsch]

1.0b4 - Released November 23, 2008

  • Filter control characters to prevent indexing errors. This fixes http://plone.org/products/collective.solr/issues/1 [witsch]
  • Avoid using brains when getting all objects from the catalog for sync runs. [witsch]
  • Prefix output from maintenance views with a time-stamp. [witsch]

1.0b3 - Released November 12, 2008

  • Fix url fallback during schema retrieval. [witsch]
  • Fix issue regarding quoting of white space when searching. [witsch]
  • Make indexing operations more robust in case the schema is missing a unique key or couldn't be parsed. [witsch]

1.0b2 - Released November 7, 2008

  • Make schema retrieval slightly more robust to not let network failures prevent access to the site. [witsch]

1.0b1 - Released November 5, 2008

  • Initial release [witsch]
 
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