Package org.apache.ignite.internal.pagemem

Class RobinHoodBackwardShiftHashMap

java.lang.Object
org.apache.ignite.internal.pagemem.RobinHoodBackwardShiftHashMap
All Implemented Interfaces:
LoadedPagesMap
public class RobinHoodBackwardShiftHashMap extends Object implements LoadedPagesMap
Loaded pages mapping to relative pointer based on Robin Hood hashing: backward shift deletion algorithm.
Performance of initial Robin Hood hashing could be greatly improved with only a little change to the removal method.
Instead of replacing entries with 'Removed' fake entries on deletion, backward shift deletion variant for the Robin Hood hashing algorithm does shift backward all the entries following the entry to delete until either an empty bucket, or a bucket with a DIB of 0 (distance to initial bucket).
Every deletion will shift backwards entries and therefore decrease their respective DIBs by 1 (all their initial DIB values would be >= 1)
This implementation stores ideal bucket with entry value itself.

  • Field Details

    • DFLT_LONG_LONG_HASH_MAP_LOAD_FACTOR

      public static final float DFLT_LONG_LONG_HASH_MAP_LOAD_FACTOR
      See Also:

  • Constructor Details

    • RobinHoodBackwardShiftHashMap

      public RobinHoodBackwardShiftHashMap(long baseAddr, long size)
      Creates map in preallocated unsafe memory segment.
      Parameters:
      baseAddr - Base buffer address.
      size - Size available for map, number of buckets (cells) to store will be determined accordingly.

  • Method Details

    • requiredMemory

      public static long requiredMemory(long elementsCnt)
      Parameters:
      elementsCnt - Maximum elements can be stored in map, its maximum size.
      Returns:
      Estimated memory size required for this map to store the given number of elements.

    • requiredMemory

      public static long requiredMemory(long elementsCnt, float loadFactor)
      Parameters:
      elementsCnt - Maximum elements can be stored in map, its maximum size.
      loadFactor - Load factor.
      Returns:
      Estimated memory size required for this map to store the given number of elements.

    • clear

      public void clear()
      Description copied from interface: LoadedPagesMap
      Removes all entries from the map.
      Specified by:
      clear in interface LoadedPagesMap

    • get

      public long get(int grpId, int pageId, int reqVer, long absent, long outdated)
      Gets value associated with the given key.
      Specified by:
      get in interface LoadedPagesMap
      Parameters:
      grpId - Cache Group ID. First part of the key.
      pageId - Page ID. Second part of the key.
      reqVer - Requested entry version, counter associated with value.
      absent - return if provided page is not presented in map.
      outdated - return if provided reqVer version is greater than value in map (was used for put).
      Returns:
      A value associated with the given key.

    • put

      public void put(int grpId, int pageId, long val, int ver)
      Associates the given key with the given value.
      Specified by:
      put in interface LoadedPagesMap
      Parameters:
      grpId - Cache Group ID. First part of the key.
      pageId - Page ID. Second part of the key.
      val - Value to set.
      ver - Version/counter associated with value, can be used to check if value is outdated.

    • remove

      public boolean remove(int grpId, int pageId)
      Removes key-value association for the given key.
      Specified by:
      remove in interface LoadedPagesMap
      Parameters:
      grpId - First part of the key. Cache Group ID.
      pageId - Second part of the key. Page ID.
      Returns:
      True if value was actually found and removed.

    • getNearestAt

      public ReplaceCandidate getNearestAt(int idxStart)
      Find nearest presented value from specified position to the right.
      Specified by:
      getNearestAt in interface LoadedPagesMap
      Parameters:
      idxStart - Index to start searching from. Bounded with LoadedPagesMap.capacity().
      Returns:
      Closest value to the index and it's partition tag or null value that will be returned if no values present.

    • refresh

      public long refresh(int grpId, int pageId, int ver)
      Refresh outdated value. Sets provided version to value associated with cache and page. Method should be called only for key present and only if version was outdated. Method may be called in case #get(int, long, int, long, long) returned outdated return value.
      Specified by:
      refresh in interface LoadedPagesMap
      Parameters:
      grpId - First part of the key. Cache Group ID.
      pageId - Second part of the key. Page ID.
      ver - Partition tag.
      Returns:
      A value associated with the given key.

    • removeIf

      public GridLongList removeIf(int startIdxToClear, int endIdxToClear, LoadedPagesMap.KeyPredicate keyPred)
      Removes entities matching provided predicate at specified mapping range.
      Specified by:
      removeIf in interface LoadedPagesMap
      Parameters:
      startIdxToClear - Index to clear value at, inclusive. Bounded with LoadedPagesMap.capacity().
      endIdxToClear - Index to clear value at, inclusive. Bounded with LoadedPagesMap.capacity().
      keyPred - Test predicate for (cache group ID, page ID).
      Returns:
      List with removed values, value is not added to list for empty cell or if key is not matching to predicate.

    • capacity

      public int capacity()
      Specified by:
      capacity in interface LoadedPagesMap
      Returns:
      Maximum number of entries in the map. This maximum can not be always reached.

    • dump

      public String dump()
      Returns:
      printable dump with all buckets state.

    • size

      public final int size()
      Specified by:
      size in interface LoadedPagesMap
      Returns:
      Current number of entries in the map.

    • forEach

      public void forEach(LoadedPagesMap.EntryConsumer act)
      Scans all the elements in this table.
      Specified by:
      forEach in interface LoadedPagesMap
      Parameters:
      act - Visitor/action to be applied to each not empty cell.