Package com.mckoi.database

Class DataCellCache

  • final class DataCellCache
extends java.lang.Object
    This object represents a cache for accesses to the the data cells within a Table. Whenever a column/row index to a cell is accessed, the cache is first checked. If the cell is not in the cache then it may go ahead and read the cell from the file.

    ISSUE: We may need to keep track of memory used. Since a String may use up much memory, we may need a cap on the maximum size the cache can grow to. For example, we wouldn't want to cache a large document. This could be handled at a higher level?

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private class  DataCellCache.DCCache
      This extends the 'Cache' class.
      private static class  DataCellCache.DCCacheKey
      Inner class that creates an object that hashes nicely over the cache source.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void alterCacheDynamics​(int max_cache_size, int max_cell_size)
      Dynamically resizes the data cell cache so it can store more/less data.
      private static int amountMemory​(TObject cell)
      Returns an approximation of the amount of memory taken by a TObject.
      (package private) static int closestPrime​(int value)
      Returns a prime number from PRIME_LIST that is the closest prime greater or equal to the given value.
      TObject get​(int table_key, int row, int column)
      Gets a TObject from the cache.
      long getCurrentCacheSize()
      Returns an estimation of the current cache size in bytes.
      void put​(int table_key, int row, int column, TObject cell)
      Puts a TObject on the cache for the given row/column of the table.
      private void reduceCacheSize​(long val)
      Reduce the cache size by the given amount.
      TObject remove​(int table_key, int row, int column)
      Removes a TObject from the cache.
      void wipe()
      Completely wipe the cache of all entries.

      • Methods inherited from class java.lang.Object

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

    • Field Detail

      • system

        private final TransactionSystem system
        The TransactionSystem that this cache is from.

      • MAX_CELL_SIZE

        private int MAX_CELL_SIZE
        The maximum size of a DataCell that is allowed to go in the cache.

      • current_cache_size

        private long current_cache_size
        The current size of the cache.

      • PRIME_LIST

        private static final int[] PRIME_LIST
        A list of primes ordered from lowest to highest.

    • Constructor Detail

      • DataCellCache

        DataCellCache​(TransactionSystem system,
              int max_cache_size,
              int max_cell_size,
              int hash_size)
        The Constructors.
        Parameters:
        max_cache_size - the maximum size in bytes that the cache is allowed to grow to (eg. 4000000).
        max_cell_size - the maximum size of an object that can be stored in the cache.
        hash_size - the number of elements in the hash (should be a prime number).

      • DataCellCache

        DataCellCache​(TransactionSystem system,
              int max_cache_size,
              int max_cell_size)

    • Method Detail

      • alterCacheDynamics

        public void alterCacheDynamics​(int max_cache_size,
                               int max_cell_size)
        Dynamically resizes the data cell cache so it can store more/less data. This is used to change cache dynamics at runtime.

      • amountMemory

        private static final int amountMemory​(TObject cell)
        Returns an approximation of the amount of memory taken by a TObject.

      • put

        public void put​(int table_key,
                int row,
                int column,
                TObject cell)
        Puts a TObject on the cache for the given row/column of the table. Ignores any cells that are larger than the maximum size.

      • get

        public TObject get​(int table_key,
                   int row,
                   int column)
        Gets a TObject from the cache. If the row/column is not in the cache then it returns null.

      • remove

        public TObject remove​(int table_key,
                      int row,
                      int column)
        Removes a TObject from the cache. This is used when we need to notify the cache that an object has become outdated. This should be used when the cell has been removed or changed. Returns the cell that was removed, or null if there was no cell at the given location.

      • wipe

        public void wipe()
        Completely wipe the cache of all entries.

      • getCurrentCacheSize

        public long getCurrentCacheSize()
        Returns an estimation of the current cache size in bytes.

      • reduceCacheSize

        private void reduceCacheSize​(long val)
        Reduce the cache size by the given amount.

      • closestPrime

        static int closestPrime​(int value)
        Returns a prime number from PRIME_LIST that is the closest prime greater or equal to the given value.