Package org.apache.lucene.store

Class NRTCachingDirectory

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    public class NRTCachingDirectory
extends Directory
    Wraps a RAMDirectory around any provided delegate directory, to be used during NRT search. Make sure you pull the merge scheduler using getMergeScheduler() and pass that to your IndexWriter; this class uses that to keep track of which merges are being done by which threads, to decide when to cache each written file.

    This class is likely only useful in a near-real-time context, where indexing rate is lowish but reopen rate is highish, resulting in many tiny files being written. This directory keeps such segments (as well as the segments produced by merging them, as long as they are small enough), in RAM.

    This is safe to use: when your app calls {IndexWriter#commit}, all cached files will be flushed from the cached and sync'd.

    NOTE: this class is somewhat sneaky in its approach for spying on merges to determine the size of a merge: it records which threads are running which merges by watching ConcurrentMergeScheduler's doMerge method. While this works correctly, likely future versions of this class will take a more general approach.

    Here's a simple example usage: 

       Directory fsDir = FSDirectory.open(new File("/path/to/index"));
   NRTCachingDirectory cachedFSDir = new NRTCachingDirectory(fsDir, 5.0, 60.0);
   IndexWriterConfig conf = new IndexWriterConfig(Version.LUCENE_32, analyzer);
   conf.setMergeScheduler(cachedFSDir.getMergeScheduler());
   IndexWriter writer = new IndexWriter(cachedFSDir, conf);

    This will cache all newly flushed segments, all merges whose expected segment size is <= 5 MB, unless the net cached bytes exceeds 60 MB at which point all writes will not be cached (until the net bytes falls below 60 MB).

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

    • Constructor Detail

      • NRTCachingDirectory

        public NRTCachingDirectory​(Directory delegate,
                           double maxMergeSizeMB,
                           double maxCachedMB)
        We will cache a newly created output if 1) it's a flush or a merge and the estimated size of the merged segment is <= maxMergeSizeMB, and 2) the total cached bytes is <= maxCachedMB

    • Method Detail

      • getLockFactory

        public LockFactory getLockFactory()
        Description copied from class: Directory
        Get the LockFactory that this Directory instance is using for its locking implementation. Note that this may be null for Directory implementations that provide their own locking implementation.
        Overrides:
        getLockFactory in class Directory

      • setLockFactory

        public void setLockFactory​(LockFactory lf)
                    throws IOException
        Description copied from class: Directory
        Set the LockFactory that this Directory instance should use for its locking implementation. Each * instance of LockFactory should only be used for one directory (ie, do not share a single instance across multiple Directories).
        Overrides:
        setLockFactory in class Directory
        Parameters:
        lf - instance of LockFactory.
        Throws:
        IOException

      • getLockID

        public String getLockID()
        Description copied from class: Directory
        Return a string identifier that uniquely differentiates this Directory instance from other Directory instances. This ID should be the same if two Directory instances (even in different JVMs and/or on different machines) are considered "the same index". This is how locking "scopes" to the right index.
        Overrides:
        getLockID in class Directory

      • clearLock

        public void clearLock​(String name)
               throws IOException
        Description copied from class: Directory
        Attempt to clear (forcefully unlock and remove) the specified lock. Only call this at a time when you are certain this lock is no longer in use.
        Overrides:
        clearLock in class Directory
        Parameters:
        name - name of the lock to be cleared.
        Throws:
        IOException

      • sizeInBytes

        public long sizeInBytes()
        Returns how many bytes are being used by the RAMDirectory cache

      • fileLength

        public long fileLength​(String name)
                throws IOException
        Description copied from class: Directory
        Returns the length of a file in the directory. This method follows the following contract:
        • Throws FileNotFoundException if the file does not exist
        • Returns a value ≥0 if the file exists, which specifies its length.
        Specified by:
        fileLength in class Directory
        Parameters:
        name - the name of the file for which to return the length.
        Throws:
        FileNotFoundException - if the file does not exist.
        IOException - if there was an IO error while retrieving the file's length.

      • listCachedFiles

        public String[] listCachedFiles()

      • sync

        public void sync​(Collection<String> fileNames)
          throws IOException
        Description copied from class: Directory
        Ensure that any writes to these files are moved to stable storage. Lucene uses this to properly commit changes to the index, to prevent a machine/OS crash from corrupting the index.

        NOTE: Clients may call this method for same files over and over again, so some impls might optimize for that. For other impls the operation can be a noop, for various reasons.
        Overrides:
        sync in class Directory
        Throws:
        IOException

      • openInput

        public IndexInput openInput​(String name,
                            int bufferSize)
                     throws IOException
        Description copied from class: Directory
        Returns a stream reading an existing file, with the specified read buffer size. The particular Directory implementation may ignore the buffer size. Currently the only Directory implementations that respect this parameter are FSDirectory and CompoundFileReader.
        Overrides:
        openInput in class Directory
        Throws:
        IOException

      • doCacheWrite

        protected boolean doCacheWrite​(String name)
        Subclass can override this to customize logic; return true if this file should be written to the RAMDirectory.