Class CollapsingQParserPlugin

  • All Implemented Interfaces:
    AutoCloseable, SolrInfoBean, SolrMetricProducer, NamedListInitializedPlugin

    public class CollapsingQParserPlugin
    extends QParserPlugin
    The CollapsingQParserPlugin is a PostFilter that performs field collapsing. This is a high performance alternative to standard Solr field collapsing (with ngroups) when the number of distinct groups in the result set is high.

    Sample syntax:

    Collapse based on the highest scoring document:

    fq=(!collapse field=field_name}

    Collapse based on the min value of a numeric field:

    fq={!collapse field=field_name min=field_name}

    Collapse based on the max value of a numeric field:

    fq={!collapse field=field_name max=field_name}

    Collapse with a null policy:

    fq={!collapse field=field_name nullPolicy=nullPolicy}

    There are three null policies:
    ignore : removes docs with a null value in the collapse field (default).
    expand : treats each doc with a null value in the collapse field as a separate group.
    collapse : collapses all docs with a null value into a single group using either highest score, or min/max.

    The CollapsingQParserPlugin fully supports the QueryElevationComponent

    • Field Detail

      • HINT_BLOCK

        public static final String HINT_BLOCK
        Indicates that values in the collapse field are unique per contiguous block, and a single pass "block based" collapse algorithm can be used. This behavior is the default for collapsing on the _root_ field, but may also be enabled for other fields that have the same characteristics. This hint will be ignored if other options prevent the use of this single pass approach (notable: nullPolicy=collapse)

        Do NOT use this hint if the index is not laid out such that each unique value in the collapse field is garuntteed to only exist in one contiguous block, otherwise the results of the collapse filter will include more then one document per collapse value.

        See Also:
        Constant Field Values

        If elevation is used in combination with the collapse query parser, we can define that we only want to return the representative and not all elevated docs by setting this parameter to false (true by default).
    • Constructor Detail

      • CollapsingQParserPlugin

        public CollapsingQParserPlugin()
    • Method Detail

      • getTopFieldCacheReader

        public static org.apache.lucene.index.LeafReader getTopFieldCacheReader​(SolrIndexSearcher searcher,
                                                                                String collapseField)
        This forces the use of the top level field cache for String fields. This is VERY fast at query time but slower to warm and causes insanity.
      • rewriteSort

        public static rewriteSort​(SortSpec sortSpec,
                                                         throws IOException
        Helper method for rewriting the Sort associated with a SortSpec. Handles the special case default of relevancy sort (ie: a SortSpec w/null Sort object)