Package org.apache.ignite.internal.processors.cache.persistence.pagemem

Class 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.

    • Constructor Detail

      • 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 Detail

      • 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.

      • get

        public long get​(int grpId,
                long 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                long outdated)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        outdated - return if provided reqVer version is greater than value in map (was used for put).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,
                long 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,
                      long 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,
                    long 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 LoadedPagesMap.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​(BiConsumer<FullPageId,​Long> 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.