## org.apache.lucene.facet.taxonomy.directory
Class DirectoryTaxonomyWriter

    java.lang.Object
      org.apache.lucene.facet.taxonomy.directory.DirectoryTaxonomyWriter

All Implemented Interfaces:
  Closeable, TaxonomyWriter, TwoPhaseCommit

    public class DirectoryTaxonomyWriter

extends Object
implements TaxonomyWriter

`TaxonomyWriter` which uses a `Directory` to store the taxonomy information on disk, and keeps an additional in-memory cache of some or all categories.

In addition to the permanently-stored information in the `Directory`, efficiency dictates that we also keep an in-memory cache of recently seen or all categories, so that we do not need to go back to disk for every category addition to see which ordinal this category already has, if any. A `TaxonomyWriterCache` object determines the specific caching algorithm used.

This class offers some hooks for extending classes to control the `IndexWriter` instance that is used. See `openIndexWriter(org.apache.lucene.store.Directory, org.apache.lucene.index.IndexWriterConfig)`.

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

Nested Class Summary
`static class` `DirectoryTaxonomyWriter.DiskOrdinalMap` `DirectoryTaxonomyWriter.OrdinalMap` maintained on file system
`static class` `DirectoryTaxonomyWriter.MemoryOrdinalMap` `DirectoryTaxonomyWriter.OrdinalMap` maintained in memory
`static interface` `DirectoryTaxonomyWriter.OrdinalMap` Mapping from old ordinal to new ordinals, used when merging indexes wit separate taxonomies.

Field Summary
`static String` `INDEX_CREATE_TIME` Property name of user commit data that contains the creation time of a taxonomy index.

Constructor Summary
`DirectoryTaxonomyWriter(Directory d)`
`DirectoryTaxonomyWriter(Directory directory, IndexWriterConfig.OpenMode openMode)` Creates a new instance with a default cached as defined by `defaultTaxonomyWriterCache()`.
`DirectoryTaxonomyWriter(Directory directory, IndexWriterConfig.OpenMode openMode, TaxonomyWriterCache cache)` Construct a Taxonomy writer.

Method Summary
`int` `addCategory(CategoryPath categoryPath)` addCategory() adds a category with a given path name to the taxonomy, and returns its ordinal.
`protected int` `addCategoryDocument(CategoryPath categoryPath, int length, int parent)`
`void` `addTaxonomy(Directory taxoDir, DirectoryTaxonomyWriter.OrdinalMap map)` Takes the categories from the given taxonomy directory, and adds the missing ones to this taxonomy.
`void` `close()` Frees used resources as well as closes the underlying `IndexWriter`, which commits whatever changes made to it to the underlying `Directory`.
`protected void` `closeResources()` A hook for extending classes to close additional resources that were used.
`void` `commit()` Calling commit() ensures that all the categories written so far are visible to a reader that is opened (or reopened) after that call.
`void` `commit(Map<String,String> commitUserData)` Like commit(), but also store properties with the index.
`protected IndexWriterConfig` `createIndexWriterConfig(IndexWriterConfig.OpenMode openMode)` Create the `IndexWriterConfig` that would be used for opening the internal index writer.
`static TaxonomyWriterCache` `defaultTaxonomyWriterCache()` Defines the default `TaxonomyWriterCache` to use in constructors which do not specify one.
`protected void` `ensureOpen()` Verifies that this instance wasn't closed, or throws `AlreadyClosedException` if it is.
`protected int` `findCategory(CategoryPath categoryPath)` Look up the given category in the cache and/or the on-disk storage, returning the category's ordinal, or a negative number in case the category does not yet exist in the taxonomy.
`int` `getCacheMemoryUsage()` Returns the number of memory bytes used by the cache.
`int` `getParent(int ordinal)` getParent() returns the ordinal of the parent category of the category with the given ordinal.
`int` `getSize()` getSize() returns the number of categories in the taxonomy.
`protected IndexWriter` `openIndexWriter(Directory directory, IndexWriterConfig config)` Open internal index writer, which contains the taxonomy data.
`protected IndexReader` `openReader()` Open an `IndexReader` from the internal `IndexWriter`, by calling `IndexReader.open(IndexWriter, boolean)`.
`void` `prepareCommit()` prepare most of the work needed for a two-phase commit.
`void` `prepareCommit(Map<String,String> commitUserData)` Like above, and also prepares to store user data with the index.
`void` `rollback()` Rollback changes to the taxonomy writer and closes the instance.
`void` `setCacheMissesUntilFill(int i)` Set the number of cache misses before an attempt is made to read the entire taxonomy into the in-memory cache.
`void` `setDelimiter(char delimiter)` setDelimiter changes the character that the taxonomy uses in its internal storage as a delimiter between category components.
`static void` `unlock(Directory directory)` Forcibly unlocks the taxonomy in the named directory.

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

Field Detail

### INDEX_CREATE_TIME

    public static final String INDEX_CREATE_TIME

  Property name of user commit data that contains the creation time of a taxonomy index.

  Applications should not use this property in their commit data because it will be overridden by this taxonomy writer.

  See Also:
    Constant Field Values

Constructor Detail

### DirectoryTaxonomyWriter

    public DirectoryTaxonomyWriter(Directory directory,
                                   IndexWriterConfig.OpenMode openMode,
                                   TaxonomyWriterCache cache)
                            throws IOException

  Construct a Taxonomy writer.

  Parameters:
    `directory` - The `Directory` in which to store the taxonomy. Note that the taxonomy is written directly to that directory (not to a subdirectory of it).
    `openMode` - Specifies how to open a taxonomy for writing: `APPEND` means open an existing index for append (failing if the index does not yet exist). `CREATE` means create a new index (first deleting the old one if it already existed). `APPEND_OR_CREATE` appends to an existing index if there is one, otherwise it creates a new index.
    `cache` - A `TaxonomyWriterCache` implementation which determines the in-memory caching policy. See for example `LruTaxonomyWriterCache` and `Cl2oTaxonomyWriterCache`. If null or missing, `defaultTaxonomyWriterCache()` is used.
  Throws:
    `CorruptIndexException` - if the taxonomy is corrupted.
    `LockObtainFailedException` - if the taxonomy is locked by another writer. If it is known that no other concurrent writer is active, the lock might have been left around by an old dead process, and should be removed using `unlock(Directory)`.
    `IOException` - if another error occurred.

### DirectoryTaxonomyWriter

    public DirectoryTaxonomyWriter(Directory directory,
                                   IndexWriterConfig.OpenMode openMode)
                            throws CorruptIndexException,
                                   LockObtainFailedException,
                                   IOException

  Creates a new instance with a default cached as defined by `defaultTaxonomyWriterCache()`.

  Throws:
    `CorruptIndexException`
    `LockObtainFailedException`
    `IOException`

### DirectoryTaxonomyWriter

    public DirectoryTaxonomyWriter(Directory d)
                            throws CorruptIndexException,
                                   LockObtainFailedException,
                                   IOException

Throws:
  `CorruptIndexException`
  `LockObtainFailedException`
  `IOException`

Method Detail

### setDelimiter

    public void setDelimiter(char delimiter)

  setDelimiter changes the character that the taxonomy uses in its internal storage as a delimiter between category components. Do not use this method unless you really know what you are doing. It has nothing to do with whatever character the application may be using to represent categories for its own use.

  If you do use this method, make sure you call it before any other methods that actually queries the taxonomy. Moreover, make sure you always pass the same delimiter for all LuceneTaxonomyWriter and LuceneTaxonomyReader objects you create for the same directory.

### unlock

    public static void unlock(Directory directory)
                       throws IOException

  Forcibly unlocks the taxonomy in the named directory.

  Caution: this should only be used by failure recovery code, when it is known that no other process nor thread is in fact currently accessing this taxonomy.

  This method is unnecessary if your `Directory` uses a `NativeFSLockFactory` instead of the default `SimpleFSLockFactory`. When the "native" lock is used, a lock does not stay behind forever when the process using it dies.

  Throws:
    `IOException`

### openIndexWriter

    protected IndexWriter openIndexWriter(Directory directory,
                                          IndexWriterConfig config)
                                   throws IOException

  Open internal index writer, which contains the taxonomy data.

  Extensions may provide their own `IndexWriter` implementation or instance.
  NOTE: the instance this method returns will be closed upon calling to `close()`.
  NOTE: the merge policy in effect must not merge none adjacent segments. See comment in `createIndexWriterConfig(IndexWriterConfig.OpenMode)` for the logic behind this.

  Parameters:
    `directory` - the `Directory` on top of which an `IndexWriter` should be opened.
    `config` - configuration for the internal index writer.
  Throws:
    `IOException`
  See Also:
    `createIndexWriterConfig(IndexWriterConfig.OpenMode)`

### createIndexWriterConfig

    protected IndexWriterConfig createIndexWriterConfig(IndexWriterConfig.OpenMode openMode)

  Create the `IndexWriterConfig` that would be used for opening the internal index writer.
  Extensions can configure the `IndexWriter` as they see fit, including setting a `merge-scheduler`, or `deletion-policy`, different RAM size etc.
  NOTE: internal docids of the configured index must not be altered. For that, categories are never deleted from the taxonomy index. In addition, merge policy in effect must not merge none adjacent segments.

  Parameters:
    `openMode` - see `IndexWriterConfig.OpenMode`
  See Also:
    `openIndexWriter(Directory, IndexWriterConfig)`

### openReader

    protected IndexReader openReader()
                              throws IOException

  Open an `IndexReader` from the internal `IndexWriter`, by calling `IndexReader.open(IndexWriter, boolean)`. Extending classes can override this method to return their own `IndexReader`.

  Throws:
    `IOException`

### defaultTaxonomyWriterCache

    public static TaxonomyWriterCache defaultTaxonomyWriterCache()

  Defines the default `TaxonomyWriterCache` to use in constructors which do not specify one.

  The current default is `Cl2oTaxonomyWriterCache` constructed with the parameters (1024, 0.15f, 3), i.e., the entire taxonomy is cached in memory while building it.

### close

    public void close()
               throws CorruptIndexException,
                      IOException

  Frees used resources as well as closes the underlying `IndexWriter`, which commits whatever changes made to it to the underlying `Directory`.

  Specified by:
    `close` in interface `Closeable`
  Throws:
    `CorruptIndexException`
    `IOException`

### getCacheMemoryUsage

    public int getCacheMemoryUsage()

  Returns the number of memory bytes used by the cache.

  Returns:
    Number of cache bytes in memory, for CL2O only; zero otherwise.

### closeResources

    protected void closeResources()
                           throws IOException

  A hook for extending classes to close additional resources that were used. The default implementation closes the `IndexReader` as well as the `TaxonomyWriterCache` instances that were used.
  NOTE: if you override this method, you should include a `super.closeResources()` call in your implementation.

  Throws:
    `IOException`

### findCategory

    protected int findCategory(CategoryPath categoryPath)
                        throws IOException

  Look up the given category in the cache and/or the on-disk storage, returning the category's ordinal, or a negative number in case the category does not yet exist in the taxonomy.

  Throws:
    `IOException`

### addCategory

    public int addCategory(CategoryPath categoryPath)
                    throws IOException

  Description copied from interface: `TaxonomyWriter`
  addCategory() adds a category with a given path name to the taxonomy, and returns its ordinal. If the category was already present in the taxonomy, its existing ordinal is returned.

  Before adding a category, addCategory() makes sure that all its ancestor categories exist in the taxonomy as well. As result, the ordinal of a category is guaranteed to be smaller then the ordinal of any of its descendants.

  Specified by:
    `addCategory` in interface `TaxonomyWriter`
  Throws:
    `IOException`

### ensureOpen

    protected final void ensureOpen()

  Verifies that this instance wasn't closed, or throws `AlreadyClosedException` if it is.

### addCategoryDocument

    protected int addCategoryDocument(CategoryPath categoryPath,
                                      int length,
                                      int parent)
                               throws CorruptIndexException,
                                      IOException

  Throws:
    `CorruptIndexException`
    `IOException`

### commit

    public void commit()
                throws CorruptIndexException,
                       IOException

  Calling commit() ensures that all the categories written so far are visible to a reader that is opened (or reopened) after that call. When the index is closed(), commit() is also implicitly done. See `TwoPhaseCommit.commit()`

  Specified by:
    `commit` in interface `TwoPhaseCommit`
  Throws:
    `CorruptIndexException`
    `IOException`

### commit

    public void commit(Map<String,String> commitUserData)
                throws CorruptIndexException,
                       IOException

  Like commit(), but also store properties with the index. These properties are retrievable by `DirectoryTaxonomyReader.getCommitUserData()`. See `TwoPhaseCommit.commit(Map)`.

  Specified by:
    `commit` in interface `TwoPhaseCommit`
  Throws:
    `CorruptIndexException`
    `IOException`
  See Also:
    `TwoPhaseCommit.commit()`, `TwoPhaseCommit.prepareCommit(Map)`

### prepareCommit

    public void prepareCommit()
                       throws CorruptIndexException,
                              IOException

  prepare most of the work needed for a two-phase commit. See `IndexWriter.prepareCommit()`.

  Specified by:
    `prepareCommit` in interface `TwoPhaseCommit`
  Throws:
    `CorruptIndexException`
    `IOException`

### prepareCommit

    public void prepareCommit(Map<String,String> commitUserData)
                       throws CorruptIndexException,
                              IOException

  Like above, and also prepares to store user data with the index. See `IndexWriter.prepareCommit(Map)`

  Specified by:
    `prepareCommit` in interface `TwoPhaseCommit`
  Throws:
    `CorruptIndexException`
    `IOException`
  See Also:
    `TwoPhaseCommit.prepareCommit()`

### getSize

    public int getSize()

  getSize() returns the number of categories in the taxonomy.

  Because categories are numbered consecutively starting with 0, it means the taxonomy contains ordinals 0 through getSize()-1.

  Note that the number returned by getSize() is often slightly higher than the number of categories inserted into the taxonomy; This is because when a category is added to the taxonomy, its ancestors are also added automatically (including the root, which always get ordinal 0).

  Specified by:
    `getSize` in interface `TaxonomyWriter`

### setCacheMissesUntilFill

    public void setCacheMissesUntilFill(int i)

  Set the number of cache misses before an attempt is made to read the entire taxonomy into the in-memory cache.

  LuceneTaxonomyWriter holds an in-memory cache of recently seen categories to speed up operation. On each cache-miss, the on-disk index needs to be consulted. When an existing taxonomy is opened, a lot of slow disk reads like that are needed until the cache is filled, so it is more efficient to read the entire taxonomy into memory at once. We do this complete read after a certain number (defined by this method) of cache misses.

  If the number is set to `0`, the entire taxonomy is read into the cache on first use, without fetching individual categories first.

  Note that if the memory cache of choice is limited in size, and cannot hold the entire content of the on-disk taxonomy, then it is never read in its entirety into the cache, regardless of the setting of this method.

### getParent

    public int getParent(int ordinal)
                  throws IOException

  Description copied from interface: `TaxonomyWriter`
  getParent() returns the ordinal of the parent category of the category with the given ordinal.

  When a category is specified as a path name, finding the path of its parent is as trivial as dropping the last component of the path. getParent() is functionally equivalent to calling getPath() on the given ordinal, dropping the last component of the path, and then calling getOrdinal() to get an ordinal back.

  If the given ordinal is the ROOT_ORDINAL, an INVALID_ORDINAL is returned. If the given ordinal is a top-level category, the ROOT_ORDINAL is returned. If an invalid ordinal is given (negative or beyond the last available ordinal), an ArrayIndexOutOfBoundsException is thrown. However, it is expected that getParent will only be called for ordinals which are already known to be in the taxonomy. TODO (Facet): instead of a getParent(ordinal) method, consider having a

  getCategory(categorypath, prefixlen) which is similar to addCategory except it doesn't add new categories; This method can be used to get the ordinals of all prefixes of the given category, and it can use exactly the same code and cache used by addCategory() so it means less code.

  Specified by:
    `getParent` in interface `TaxonomyWriter`
  Throws:
    `IOException`

### addTaxonomy

    public void addTaxonomy(Directory taxoDir,
                            DirectoryTaxonomyWriter.OrdinalMap map)
                     throws IOException

  Takes the categories from the given taxonomy directory, and adds the missing ones to this taxonomy. Additionally, it fills the given `DirectoryTaxonomyWriter.OrdinalMap` with a mapping from the original ordinal to the new ordinal.

  Throws:
    `IOException`

### rollback

    public void rollback()
                  throws IOException

  Rollback changes to the taxonomy writer and closes the instance. Following this method the instance becomes unusable (calling any of its API methods will yield an `AlreadyClosedException`).

  Specified by:
    `rollback` in interface `TwoPhaseCommit`
  Throws:
    `IOException`