Package org.apache.lucene.util

Class RamUsageEstimator

java.lang.Object
org.apache.lucene.util.RamUsageEstimator
public final class RamUsageEstimator extends Object
Estimates the size (memory representation) of Java objects.
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  • Field Details

    • JVM_INFO_STRING

      public static final String JVM_INFO_STRING
      JVM info string for debugging and reports.

    • ONE_KB

      public static final long ONE_KB
      One kilobyte bytes.
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    • ONE_MB

      public static final long ONE_MB
      One megabyte bytes.
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    • ONE_GB

      public static final long ONE_GB
      One gigabyte bytes.
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    • NUM_BYTES_BOOLEAN

      public static final int NUM_BYTES_BOOLEAN
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    • NUM_BYTES_BYTE

      public static final int NUM_BYTES_BYTE
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    • NUM_BYTES_CHAR

      public static final int NUM_BYTES_CHAR
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    • NUM_BYTES_SHORT

      public static final int NUM_BYTES_SHORT
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    • NUM_BYTES_INT

      public static final int NUM_BYTES_INT
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    • NUM_BYTES_FLOAT

      public static final int NUM_BYTES_FLOAT
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    • NUM_BYTES_LONG

      public static final int NUM_BYTES_LONG
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    • NUM_BYTES_DOUBLE

      public static final int NUM_BYTES_DOUBLE
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    • NUM_BYTES_OBJECT_REF

      public static final int NUM_BYTES_OBJECT_REF
      Number of bytes this jvm uses to represent an object reference.

    • NUM_BYTES_OBJECT_HEADER

      public static final int NUM_BYTES_OBJECT_HEADER
      Number of bytes to represent an object header (no fields, no alignments).

    • NUM_BYTES_ARRAY_HEADER

      public static final int NUM_BYTES_ARRAY_HEADER
      Number of bytes to represent an array header (no content, but with alignments).

    • NUM_BYTES_OBJECT_ALIGNMENT

      public static final int NUM_BYTES_OBJECT_ALIGNMENT
      A constant specifying the object alignment boundary inside the JVM. Objects will always take a full multiple of this constant, possibly wasting some space.

  • Method Details

    • isSupportedJVM

      public static boolean isSupportedJVM()
      Returns true, if the current JVM is fully supported by RamUsageEstimator. If this method returns false you are maybe using a 3rd party Java VM that is not supporting Oracle/Sun private APIs. The memory estimates can be imprecise then (no way of detecting compressed references, alignments, etc.). Lucene still tries to use sensible defaults.

    • alignObjectSize

      public static long alignObjectSize(long size)
      Aligns an object size to be the next multiple of NUM_BYTES_OBJECT_ALIGNMENT.

    • sizeOf

      public static long sizeOf(byte[] arr)
      Returns the size in bytes of the byte[] object.

    • sizeOf

      public static long sizeOf(boolean[] arr)
      Returns the size in bytes of the boolean[] object.

    • sizeOf

      public static long sizeOf(char[] arr)
      Returns the size in bytes of the char[] object.

    • sizeOf

      public static long sizeOf(short[] arr)
      Returns the size in bytes of the short[] object.

    • sizeOf

      public static long sizeOf(int[] arr)
      Returns the size in bytes of the int[] object.

    • sizeOf

      public static long sizeOf(float[] arr)
      Returns the size in bytes of the float[] object.

    • sizeOf

      public static long sizeOf(long[] arr)
      Returns the size in bytes of the long[] object.

    • sizeOf

      public static long sizeOf(double[] arr)
      Returns the size in bytes of the double[] object.

    • sizeOf

      public static long sizeOf(Object obj)
      Estimates the RAM usage by the given object. It will walk the object tree and sum up all referenced objects.

      Resource Usage: This method internally uses a set of every object seen during traversals so it does allocate memory (it isn't side-effect free). After the method exits, this memory should be GCed.

    • shallowSizeOf

      public static long shallowSizeOf(Object obj)
      Estimates a "shallow" memory usage of the given object. For arrays, this will be the memory taken by array storage (no subreferences will be followed). For objects, this will be the memory taken by the fields. JVM object alignments are also applied.

    • shallowSizeOfInstance

      public static long shallowSizeOfInstance(Class<?> clazz)
      Returns the shallow instance size in bytes an instance of the given class would occupy. This works with all conventional classes and primitive types, but not with arrays (the size then depends on the number of elements and varies from object to object).
      Throws:
      IllegalArgumentException - if clazz is an array class.
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    • getUnsupportedFeatures

      public static EnumSet<RamUsageEstimator.JvmFeature> getUnsupportedFeatures()
      Return the set of unsupported JVM features that improve the estimation.

    • getSupportedFeatures

      public static EnumSet<RamUsageEstimator.JvmFeature> getSupportedFeatures()
      Return the set of supported JVM features that improve the estimation.

    • humanReadableUnits

      public static String humanReadableUnits(long bytes)
      Returns size in human-readable units (GB, MB, KB or bytes).

    • humanReadableUnits

      public static String humanReadableUnits(long bytes, DecimalFormat df)
      Returns size in human-readable units (GB, MB, KB or bytes).

    • humanSizeOf

      public static String humanSizeOf(Object object)
      Return a human-readable size of a given object.
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