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## org.apache.lucene.facet.taxonomy.writercache.cl2o
Class CompactLabelToOrdinal

    java.lang.Object
      org.apache.lucene.facet.taxonomy.writercache.cl2o.LabelToOrdinal
          org.apache.lucene.facet.taxonomy.writercache.cl2o.CompactLabelToOrdinal

    public class CompactLabelToOrdinal

extends LabelToOrdinal

This is a very efficient LabelToOrdinal implementation that uses a CharBlockArray to store all labels and a configurable number of HashArrays to reference the labels.

Since the HashArrays don't handle collisions, a `CollisionMap` is used to store the colliding labels.

This data structure grows by adding a new HashArray whenever the number of collisions in the `CollisionMap` exceeds `loadFactor` * `LabelToOrdinal.getMaxOrdinal()`. Growing also includes reinserting all colliding labels into the HashArrays to possibly reduce the number of collisions. For setting the `loadFactor` see `CompactLabelToOrdinal(int, float, int)`.

This data structure has a much lower memory footprint (~30%) compared to a Java HashMap. It also only uses a small fraction of objects a HashMap would use, thus limiting the GC overhead. Ingestion speed was also ~50% faster compared to a HashMap for 3M unique labels.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Field Summary
`static float` | `DefaultLoadFactor`

Fields inherited from class org.apache.lucene.facet.taxonomy.writercache.cl2o.LabelToOrdinal
`counter, InvalidOrdinal`

Constructor Summary
`CompactLabelToOrdinal(int initialCapacity, float loadFactor, int numHashArrays)`

Method Summary
`void` | `addLabel(CategoryPath label, int ordinal)` Adds a new label if its not yet in the table.
`void` | `addLabel(CategoryPath label, int prefixLen, int ordinal)` Adds a new label if its not yet in the table.
`int` | `getOrdinal(CategoryPath label)`
`int` | `getOrdinal(CategoryPath label, int prefixLen)`
`int` | `sizeOfMap()`

Methods inherited from class org.apache.lucene.facet.taxonomy.writercache.cl2o.LabelToOrdinal
`getMaxOrdinal, getNextOrdinal`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### DefaultLoadFactor

    public static final float DefaultLoadFactor

See Also:
  Constant Field Values

Constructor Detail

### CompactLabelToOrdinal

    public CompactLabelToOrdinal(int initialCapacity,
                                 float loadFactor,
                                 int numHashArrays)

Method Detail

### sizeOfMap

    public int sizeOfMap()

### addLabel

    public void addLabel(CategoryPath label,
                         int ordinal)

  Description copied from class: `LabelToOrdinal`
  Adds a new label if its not yet in the table. Throws an `IllegalArgumentException` if the same label with a different ordinal was previoulsy added to this table.

  Specified by:
    `addLabel` in class `LabelToOrdinal`

### addLabel

    public void addLabel(CategoryPath label,
                         int prefixLen,
                         int ordinal)

  Description copied from class: `LabelToOrdinal`
  Adds a new label if its not yet in the table. Throws an `IllegalArgumentException` if the same label with a different ordinal was previoulsy added to this table.

  Specified by:
    `addLabel` in class `LabelToOrdinal`

### getOrdinal

    public int getOrdinal(CategoryPath label)

  Specified by:
    `getOrdinal` in class `LabelToOrdinal`
  Returns:
    the ordinal assigned to the given label, or `LabelToOrdinal.InvalidOrdinal` if the label cannot be found in this table.

### getOrdinal

    public int getOrdinal(CategoryPath label,
                          int prefixLen)

  Specified by:
    `getOrdinal` in class `LabelToOrdinal`
  Returns:
    the ordinal assigned to the given label, or `LabelToOrdinal.InvalidOrdinal` if the label cannot be found in this table.

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