Apache Solr Reference Guide Covering Apache Solr 6.0

Levenshtein metric, which is the same metric used with the other spell checker implementations.
Because this spell checker is querying the main index, you may want to limit how often it queries the index to be
sure to avoid any performance conflicts with user queries. The accuracy setting defines the threshold for a valid
suggestion, while maxEdits defines the number of changes to the term to allow. Since most spelling mistakes
are only 1 letter off, setting this to 1 will reduce the number of possible suggestions (the default, however, is 2);
the value can only be 1 or 2. minPrefix defines the minimum number of characters the terms should share.
Setting this to 1 means that the spelling suggestions will all start with the same letter, for example.
The maxInspections parameter defines the maximum number of possible matches to review before returning
results; the default is 5. minQueryLength defines how many characters must be in the query before
suggestions are provided; the default is 4. maxQueryFrequency sets the maximum threshold for the number of
documents a term must appear in before being considered as a suggestion. This can be a percentage (such as
.01, or 1%) or an absolute value (such as 4). A lower threshold is better for small indexes. Finally, tresholdTok
enFrequency sets the minimum number of documents a term must appear in, and can also be expressed as a
percentage or an absolute value.
FileBasedSpellChecker
The FileBasedSpellChecker uses an external file as a spelling dictionary. This can be useful if using Solr as
a spelling server, or if spelling suggestions don't need to be based on actual terms in the index. In solrconfig
.xml, you would define the searchComponent as so:
solr.FileBasedSpellChecker
file
spellings.txt
UTF-8
./spellcheckerFile
The differences here are the use of the sourceLocation to define the location of the file of terms and the use
of characterEncoding to define the encoding of the terms file.
In the previous example, name is used to name this specific definition of the spellchecker. Multiple
definitions can co-exist in a single solrconfig.xml, and the name helps to differentiate them. If only
defining one spellchecker, no name is required.
WordBreakSolrSpellChecker
WordBreakSolrSpellChecker offers suggestions by combining adjacent query terms and/or breaking terms
into multiple words. It is a SpellCheckComponent enhancement, leveraging Lucene's WordBreakSpellChec
ker. It can detect spelling errors resulting from misplaced whitespace without the use of shingle-based
dictionaries and provides collation support for word-break errors, including cases where the user has a mix of
single-word spelling errors and word-break errors in the same query. It also provides shard support.
Here is how it might be configured in solrconfig.xml:
Apache Solr Reference Guide 6.0
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