The facet Parameter
If set to true, this parameter enables facet counts in the query response. If set to false, a blank or missing value, this parameter disables faceting. None of the other parameters listed below will have any effect unless this parameter is set to true. The default value is blank (false).
The facet.query Parameter
This parameter allows you to specify an arbitrary query in the Lucene default syntax to generate a facet count.
By default, Solr?s faceting feature automatically determines the unique terms for a field and returns a count for each of those terms. Using facet.query, you can override this default behavior and select exactly which terms or expressions you would like to see counted. In a typical implementation of faceting, you will specify a number of facet.query parameters. This parameter can be particularly useful for numeric-range-based facets or prefix-based facets.
You can set the facet.query parameter multiple times to indicate that multiple queries should be used as separate facet constraints.
To use facet queries in a syntax other than the default syntax, prefix the facet query with the name of the query notation. For example, to use the hypothetical myfunc query parser, you could set the facet.query parameter like so:
facet.query={!myfunc}name~fred
Field-Value Faceting Parameters
Several parameters can be used to trigger faceting based on the indexed terms in a field.
When using these parameters, it is important to remember that "term" is a very specific concept in Lucene: it relates to the literal field/value pairs that are indexed after any analysis occurs. For text fields that include stemming, lowercasing, or word splitting, the resulting terms may not be what you expect.
If you want Solr to perform both analysis (for searching) and faceting on the full literal strings, use the copyField directive in your Schema to create two versions of the field: one Text and one String.
The facet.field Parameter
The facet.field parameter identifies a field that should be treated as a facet. It iterates over each Term in the field and generate a facet count using that Term as the constraint. This parameter can be specified multiple times in a query to select multiple facet fields.
The facet.prefix Parameter
The facet.prefix parameter limits the terms on which to facet to those starting with the given string prefix. This does not limit the query in any way, only the facets that would be returned in response to the query.
This parameter can be specified on a per-field basis with the syntax of f..facet.prefix.
The facet.contains Parameter
The facet.contains parameter limits the terms on which to facet to those containing the given substring. This does not limit the query in any way, only the facets that would be returned in response to the query.
This parameter can be specified on a per-field basis with the syntax of f..facet.contains.
The facet.contains.ignoreCase Parameter
If facet.contains is used, the facet.contains.ignoreCase parameter causes case to be ignored when matching the given substring against candidate facet terms.
This parameter can be specified on a per-field basis with the syntax of f..facet.contains.ignoreCase.
The facet.sort Parameter
This parameter determines the ordering of the facet field constraints.
There are two options for this parameter.
count
Sort the constraints by count (highest count first).
index
Return the constraints sorted in their index order (lexicographic by indexed term). For terms in the ASCII range, this will be alphabetically sorted.
The default is count if facet.limit is greater than 0, otherwise, the default is index.
This parameter can be specified on a per-field basis with the syntax of f..facet.sort.
The facet.limit Parameter
This parameter specifies the maximum number of constraint counts (essentially, the number of facets for a field that are returned) that should be returned for the facet fields. A negative value means that Solr will return unlimited number of constraint counts.
The default value is 100.
This parameter can be specified on a per-field basis to apply a distinct limit to each field with the syntax of f..facet.limit.
The facet.offset Parameter
The facet.offset parameter indicates an offset into the list of constraints to allow paging.
The default value is 0.
This parameter can be specified on a per-field basis with the syntax of f..facet.offset.
The facet.mincount Parameter
The facet.mincount parameter specifies the minimum counts required for a facet field to be included in the response. If a field?s counts are below the minimum, the field?s facet is not returned.
The default value is 0.
This parameter can be specified on a per-field basis with the syntax of f..facet.mincount.
The facet.missing Parameter
If set to true, this parameter indicates that, in addition to the Term-based constraints of a facet field, a count of all results that match the query but which have no facet value for the field should be computed and returned in the response.
The default value is false.
This parameter can be specified on a per-field basis with the syntax of f..facet.missing.
The facet.method Parameter
The facet.method parameter selects the type of algorithm or method Solr should use when faceting a field.
The following methods are available.
enum
Enumerates all terms in a field, calculating the set intersection of documents that match the term with documents that match the query.
This method is recommended for faceting multi-valued fields that have only a few distinct values. The average number of values per document does not matter.
For example, faceting on a field with U.S. States such as Alabama, Alaska, ? Wyoming would lead to fifty cached filters which would be used over and over again. The filterCache should be large enough to hold all the cached filters.
fc
Calculates facet counts by iterating over documents that match the query and summing the terms that appear in each document.
This is currently implemented using an UnInvertedField cache if the field either is multi-valued or is tokenized (according to FieldType.isTokened()). Each document is looked up in the cache to see what terms/values it contains, and a tally is incremented for each value.
This method is excellent for situations where the number of indexed values for the field is high, but the number of values per document is low. For multi-valued fields, a hybrid approach is used that uses term filters from the filterCache for terms that match many documents. The letters fc stand for field cache.
fcs
Per-segment field faceting for single-valued string fields. Enable with facet.method=fcs and control the number of threads used with the threads local parameter. This parameter allows faceting to be faster in the presence of rapid index changes.
The default value is fc (except for fields using the BoolField field type and when facet.exists=true is requested) since it tends to use less memory and is faster when a field has many unique terms in the index.
This parameter can be specified on a per-field basis with the syntax of f..facet.method.
The facet.enum.cache.minDf Parameter
This parameter indicates the minimum document frequency (the number of documents matching a term) for which the filterCache should be used when determining the constraint count for that term. This is only used with the facet.method=enum method of faceting.
A value greater than zero decreases the filterCache?s memory usage, but increases the time required for the query to be processed. If you are faceting on a field with a very large number of terms, and you wish to decrease memory usage, try setting this parameter to a value between 25 and 50, and run a few tests. Then, optimize the parameter setting as necessary.
The default value is 0, causing the filterCache to be used for all terms in the field.
This parameter can be specified on a per-field basis with the syntax of f..facet.enum.cache.minDf.
The facet.exists Parameter
To cap facet counts by 1, specify facet.exists=true. It can be used with facet.method=enum or when it?s omitted. It can be used only on non-trie fields (such as strings). It may speed up facet counting on large indices and/or high-cardinality facet values..
This parameter can be specified on a per-field basis with the syntax of f..facet.exists or via local parameter` facet.field={!facet.method=enum facet.exists=true}size`.
The facet.excludeTerms Parameter
If you want to remove terms from facet counts but keep them in the index, the facet.excludeTerms parameter allows you to do that.
Over-Request Parameters
In some situations, the accuracy in selecting the "top" constraints returned for a facet in a distributed Solr query can be improved by "Over Requesting" the number of desired constraints (ie: facet.limit) from each of the individual Shards. In these situations, each shard is by default asked for the top ?10 + (1.5 * facet.limit)? constraints.
In some situations, depending on how your docs are partitioned across your shards, and what facet.limit value you used, you may find it advantageous to increase or decrease the amount of over-requesting Solr does. This can be achieved by setting the facet.overrequest.count (defaults to 10) and facet.overrequest.ratio (defaults to 1.5) parameters.
The facet.threads Parameter
This param will cause loading the underlying fields used in faceting to be executed in parallel with the number of threads specified. Specify as facet.threads=N where N is the maximum number of threads used. Omitting this parameter or specifying the thread count as 0 will not spawn any threads, and only the main request thread will be used. Specifying a negative number of threads will create up to Integer.MAX_VALUE threads.
