Package org.apache.cassandra.io.sstable

Class Downsampling

java.lang.Object
org.apache.cassandra.io.sstable.Downsampling
public class Downsampling extends Object

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    BASE_SAMPLING_LEVEL
    The base (down)sampling level determines the granularity at which we can down/upsample.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Downsampling()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    static int
    getEffectiveIndexIntervalAfterIndex(int index, int samplingLevel, int minIndexInterval)
    Calculates the effective index interval after the entry at `index` in an IndexSummary.
    static List<Integer>
    getOriginalIndexes(int samplingLevel)
    Returns a list that can be used to translate current index summary indexes to their original index before downsampling.
    static List<Integer>
    getSamplingPattern(int samplingLevel)
    Gets a list L of starting indices for downsampling rounds: the first round should start with the offset given by L[0], the second by the offset in L[1], etc.
    static int[]
    getStartPoints(int currentSamplingLevel, int newSamplingLevel)
     

    Methods inherited from class java.lang.Object

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

  • Field Details

    • BASE_SAMPLING_LEVEL

      public static final int BASE_SAMPLING_LEVEL
      The base (down)sampling level determines the granularity at which we can down/upsample. A higher number allows us to approximate more closely the ideal sampling. (It could also mean we do a lot of expensive almost-no-op resamplings from N to N-1, but the thresholds in IndexSummaryManager prevent that.) BSL must be a power of two in order to have good sampling patterns. This cannot be changed without rebuilding all index summaries at full sampling; for now we treat it as a constant.
      See Also:

  • Constructor Details

    • Downsampling

      public Downsampling()

  • Method Details

    • getSamplingPattern

      public static List<Integer> getSamplingPattern(int samplingLevel)
      Gets a list L of starting indices for downsampling rounds: the first round should start with the offset given by L[0], the second by the offset in L[1], etc.
      Parameters:
      samplingLevel - the base sampling level
      Returns:
      A list of `samplingLevel` unique indices between 0 and `samplingLevel`

    • getOriginalIndexes

      public static List<Integer> getOriginalIndexes(int samplingLevel)
      Returns a list that can be used to translate current index summary indexes to their original index before downsampling. (This repeats every `samplingLevel`, so that's how many entries we return.) For example, if [0, 64] is returned, the current index summary entry at index 0 was originally at index 0, and the current index 1 was originally at index 64.
      Parameters:
      samplingLevel - the current sampling level for the index summary
      Returns:
      a list of original indexes for current summary entries

    • getEffectiveIndexIntervalAfterIndex

      public static int getEffectiveIndexIntervalAfterIndex(int index, int samplingLevel, int minIndexInterval)
      Calculates the effective index interval after the entry at `index` in an IndexSummary. In other words, this returns the number of partitions in the primary on-disk index before the next partition that has an entry in the index summary. If samplingLevel == BASE_SAMPLING_LEVEL, this will be equal to the index interval.
      Parameters:
      index - an index into an IndexSummary
      samplingLevel - the current sampling level for that IndexSummary
      minIndexInterval - the min index interval (effective index interval at full sampling)
      Returns:
      the number of partitions before the next index summary entry, inclusive on one end

    • getStartPoints

      public static int[] getStartPoints(int currentSamplingLevel, int newSamplingLevel)