Package com.mckoi.database

Class IndexStore

  • public final class IndexStore
extends java.lang.Object
    A class that manages the storage of a set of transactional index lists in a way that is fast to modify. This class has a number of objectives;

    • To prevent corruption as best as possible.
    • To be able to modify lists of integers very fast and persistantly.
    • To have size optimization features such as defragmentation.
    • To provide very fast searches on sorted lists (caching features).
    • To be able to map a list to an IntegerListInterface interface.

    None intuitively, this object also handles unique ids.

    Author:
    Tobias Downer

    • Constructor Summary

      Constructors 
      Constructor Description
      IndexStore​(java.io.File file_name, DebugLogger logger)
      Constructs the IndexStore.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void addIndexLists​(int count, byte type)
      Adds a number of blank index tables to the index store.
      void close()
      Cleanly closes the index store.
      void commitIndexSet​(IndexSet index_set)
      Commits changes made to a snapshop of an IndexSet as being permanent changes to the state of the index store.
      void copyTo​(java.io.File path)
      Copies the persistant part of this to another store.
      void create​(int block_size)
      Creates a new black index store and returns leaving the newly created store in an open state.
      void delete()
      Deletes the store.
      boolean exists()
      Returns true if the index store file exists.
      boolean fix​(UserTerminal terminal)
      Performs checks to determine that the index store is stable.
      void flush()
      Flushes all information in this index store to the file representing this store in the file system.
      IndexSet getSnapshotIndexSet()
      Returns a current snapshot of the current indexes that are committed in this store.
      void hardSynch()
      Performs a hard synchronization of this index store.
      void init()
      Initializes the IndexStore.
      boolean isReadOnly()
      Returns true if this store is read only.
      boolean open​(boolean read_only)
      Opens this index store.
      java.lang.String statusString()
      Returns a string that contains diagnostic information.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • IndexStore

        public IndexStore​(java.io.File file_name,
                  DebugLogger logger)
        Constructs the IndexStore.
        Parameters:
        file_name - the path to the file of the index store in the file system.

    • Method Detail

      • exists

        public boolean exists()
               throws java.io.IOException
        Returns true if the index store file exists.
        Throws:
        java.io.IOException

      • create

        public void create​(int block_size)
            throws java.io.IOException
        Creates a new black index store and returns leaving the newly created store in an open state. This method initializes the various data in the index store for a blank set of index tables. Must call the 'init' method after this is called.

        Parameters:
        block_size - the number of ints stored in each block. This can be optimized for specific use. Must be between 0 and 32768.
        Throws:
        java.io.IOException

      • open

        public boolean open​(boolean read_only)
             throws java.io.IOException
        Opens this index store. If 'read_only' is set to true then the store is opened in read only mode.

        Returns true if opening the store was dirty (was not closed properly) and may need repair.

        If the index store does not exist before this method is called then it is created.

        Throws:
        java.io.IOException

      • init

        public void init()
          throws java.io.IOException
        Initializes the IndexStore. Must be called after it is opened for normal use, however it should not be called if we are fixing or repairing the store.
        Throws:
        java.io.IOException

      • fix

        public boolean fix​(UserTerminal terminal)
            throws java.io.IOException
        Performs checks to determine that the index store is stable. If an IndexStore is not stable and can not be fixed cleanly then it deletes all information in the store and returns false indicating the index information must be rebuilt.

        Assumes the index store has been opened previous to calling this.

        Returns true if the IndexStore is stable.

        Throws:
        java.io.IOException

      • isReadOnly

        public boolean isReadOnly()
        Returns true if this store is read only.

      • delete

        public void delete()
        Deletes the store. Must have been closed before this is called.

      • copyTo

        public void copyTo​(java.io.File path)
            throws java.io.IOException
        Copies the persistant part of this to another store. Must be open when this is called.
        Throws:
        java.io.IOException

      • close

        public void close()
           throws java.io.IOException
        Cleanly closes the index store.
        Throws:
        java.io.IOException

      • flush

        public void flush()
           throws java.io.IOException
        Flushes all information in this index store to the file representing this store in the file system. This is called to persistantly update the state of the index store.
        Throws:
        java.io.IOException

      • hardSynch

        public void hardSynch()
               throws java.io.IOException
        Performs a hard synchronization of this index store. This will force the OS to synchronize the contents of the data store.

        For this to be useful, 'flush' should be called before a hardSynch.

        Throws:
        java.io.IOException

      • addIndexLists

        public void addIndexLists​(int count,
                          byte type)
        Adds a number of blank index tables to the index store. For example, we may want this store to contain 16 index lists.

        NOTE: This doesn't write the updated information to the file. You must call 'flush' to write the information to the store.

      • getSnapshotIndexSet

        public IndexSet getSnapshotIndexSet()
        Returns a current snapshot of the current indexes that are committed in this store. The returned object can be used to create mutable IntegerListInterface objects. The created index lists are isolated from changes made to the rest of the indexes after this method returns.

        A transaction must grab an IndexSet object when it opens.

        NOTE: We MUST guarentee that the IndexSet is disposed when the transaction finishes.

      • commitIndexSet

        public void commitIndexSet​(IndexSet index_set)
        Commits changes made to a snapshop of an IndexSet as being permanent changes to the state of the index store. This will generate an error if the given IndexSet is not the last set returned from the 'getSnapshotIndexSet' method.

        For this to be used, during the transaction commit function a 'getSnapshopIndexSet' must be obtained, changes made to it from info in the journal, then a call to this method. There must be a guarentee that 'getSnapshotIndexSet' is not called again during this process.

        NOTE: This doesn't write the updated information to the file. You must call 'flush' to write the information to the store.

        NOTE: We must be guarenteed that when this method is called no other calls to other methods in this object can be called.

      • statusString

        public java.lang.String statusString()
                              throws java.io.IOException
        Returns a string that contains diagnostic information.
        Throws:
        java.io.IOException