RamUsageEstimator (Lucene 8.9.0 API)乐学网一站式学习平台

java.lang.Object
- org.apache.lucene.util.RamUsageEstimator

```
public final class RamUsageEstimator
extends Object
```
Estimates the size (memory representation) of Java objects.
This class uses assumptions that were discovered for the Hotspot virtual machine. If you use a non-OpenJDK/Oracle-based JVM, the measurements may be slightly wrong.

See Also:

shallowSizeOf(Object), shallowSizeOfInstance(Class)

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Field Summary

Fields
Modifier and Type	Field and Description
`static boolean`	`COMPRESSED_REFS_ENABLED` True, iff compressed references (oops) are enabled by this JVM
`static long`	`HASHTABLE_RAM_BYTES_PER_ENTRY` Approximate memory usage that we assign to a Hashtable / HashMap entry.
`static long`	`LINKED_HASHTABLE_RAM_BYTES_PER_ENTRY` Approximate memory usage that we assign to a LinkedHashMap entry.
`static int`	`MAX_DEPTH` Recurse only into immediate descendants.
`static int`	`NUM_BYTES_ARRAY_HEADER` Number of bytes to represent an array header (no content, but with alignments).
`static int`	`NUM_BYTES_OBJECT_ALIGNMENT` A constant specifying the object alignment boundary inside the JVM.
`static int`	`NUM_BYTES_OBJECT_HEADER` Number of bytes to represent an object header (no fields, no alignments).
`static int`	`NUM_BYTES_OBJECT_REF` Number of bytes this JVM uses to represent an object reference.
`static long`	`ONE_GB` One gigabyte bytes.
`static long`	`ONE_KB` One kilobyte bytes.
`static long`	`ONE_MB` One megabyte bytes.
`static Map<Class<?>,Integer>`	`primitiveSizes` Sizes of primitive classes.
`static int`	`QUERY_DEFAULT_RAM_BYTES_USED` Approximate memory usage that we assign to all unknown queries - this maps roughly to a BooleanQuery with a couple term clauses.
`static int`	`UNKNOWN_DEFAULT_RAM_BYTES_USED` Approximate memory usage that we assign to all unknown objects - this maps roughly to a few primitive fields and a couple short String-s.

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static long`	`alignObjectSize(long size)` Aligns an object size to be the next multiple of `NUM_BYTES_OBJECT_ALIGNMENT`.
`static String`	`humanReadableUnits(long bytes)` Returns `size` in human-readable units (GB, MB, KB or bytes).
`static String`	`humanReadableUnits(long bytes, DecimalFormat df)` Returns `size` in human-readable units (GB, MB, KB or bytes).
`static long`	`shallowSizeOf(Object obj)` Estimates a "shallow" memory usage of the given object.
`static long`	`shallowSizeOf(Object[] arr)` Returns the shallow size in bytes of the Object[] object.
`static long`	`shallowSizeOfInstance(Class<?> clazz)` Returns the shallow instance size in bytes an instance of the given class would occupy.
`static long`	`sizeOf(Accountable accountable)` Returns the size in bytes of the `Accountable` object, using its `Accountable.ramBytesUsed()` method.
`static long`	`sizeOf(Accountable[] accountables)` Return the size of the provided array of `Accountable`s by summing up the shallow size of the array and the `memory usage` reported by each `Accountable`.
`static long`	`sizeOf(boolean[] arr)` Returns the size in bytes of the boolean[] object.
`static long`	`sizeOf(byte[] arr)` Returns the size in bytes of the byte[] object.
`static long`	`sizeOf(char[] arr)` Returns the size in bytes of the char[] object.
`static long`	`sizeOf(double[] arr)` Returns the size in bytes of the double[] object.
`static long`	`sizeOf(float[] arr)` Returns the size in bytes of the float[] object.
`static long`	`sizeOf(int[] arr)` Returns the size in bytes of the int[] object.
`static long`	`sizeOf(Long value)` Return the size of the provided `Long` object, returning 0 if it is cached by the JVM and its shallow size otherwise.
`static long`	`sizeOf(long[] arr)` Returns the size in bytes of the long[] object.
`static long`	`sizeOf(Query q)` Returns the size in bytes of a Query object.
`static long`	`sizeOf(Query q, long defSize)` Returns the size in bytes of a Query object.
`static long`	`sizeOf(short[] arr)` Returns the size in bytes of the short[] object.
`static long`	`sizeOf(String s)` Returns the size in bytes of the String object.
`static long`	`sizeOf(String[] arr)` Returns the size in bytes of the String[] object.
`static long`	`sizeOfCollection(Collection<?> collection)` Returns the size in bytes of a Collection object, including sizes of its values, supplying `UNKNOWN_DEFAULT_RAM_BYTES_USED` when object type is not well known.
`static long`	`sizeOfCollection(Collection<?> collection, long defSize)` Returns the size in bytes of a Collection object, including sizes of its values, supplying default object size when object type is not well known.
`static long`	`sizeOfMap(Map<?,?> map)` Returns the size in bytes of a Map object, including sizes of its keys and values, supplying `UNKNOWN_DEFAULT_RAM_BYTES_USED` when object type is not well known.
`static long`	`sizeOfMap(Map<?,?> map, long defSize)` Returns the size in bytes of a Map object, including sizes of its keys and values, supplying default object size when object type is not well known.
`static long`	`sizeOfObject(Object o)` Best effort attempt to estimate the size in bytes of an undetermined object.
`static long`	`sizeOfObject(Object o, long defSize)` Best effort attempt to estimate the size in bytes of an undetermined object.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - ONE_KB
```
public static final long ONE_KB
```
    One kilobyte bytes.
    
    See Also:
    
    Constant Field Values
  - ONE_MB
```
public static final long ONE_MB
```
    One megabyte bytes.
    
    See Also:
    
    Constant Field Values
  - ONE_GB
```
public static final long ONE_GB
```
    One gigabyte bytes.
    
    See Also:
    
    Constant Field Values
  - COMPRESSED_REFS_ENABLED
```
public static final boolean COMPRESSED_REFS_ENABLED
```
    True, iff compressed references (oops) are enabled by this JVM
  - 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.
  - QUERY_DEFAULT_RAM_BYTES_USED
```
public static final int QUERY_DEFAULT_RAM_BYTES_USED
```
    Approximate memory usage that we assign to all unknown queries - this maps roughly to a BooleanQuery with a couple term clauses.
    
    See Also:
    
    Constant Field Values
  - UNKNOWN_DEFAULT_RAM_BYTES_USED
```
public static final int UNKNOWN_DEFAULT_RAM_BYTES_USED
```
    Approximate memory usage that we assign to all unknown objects - this maps roughly to a few primitive fields and a couple short String-s.
    
    See Also:
    
    Constant Field Values
  - primitiveSizes
```
public static final Map<Class<?>,Integer> primitiveSizes
```
    Sizes of primitive classes.
  - HASHTABLE_RAM_BYTES_PER_ENTRY
```
public static final long HASHTABLE_RAM_BYTES_PER_ENTRY
```
    Approximate memory usage that we assign to a Hashtable / HashMap entry.
  - LINKED_HASHTABLE_RAM_BYTES_PER_ENTRY
```
public static final long LINKED_HASHTABLE_RAM_BYTES_PER_ENTRY
```
    Approximate memory usage that we assign to a LinkedHashMap entry.
  - MAX_DEPTH
```
public static final int MAX_DEPTH
```
    Recurse only into immediate descendants.
    
    See Also:
    
    Constant Field Values
- Method Detail
  - 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(Long value)
```
    Return the size of the provided Long object, returning 0 if it is cached by the JVM and its shallow size otherwise.
  - 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(String[] arr)
```
    Returns the size in bytes of the String[] object.
  - sizeOfMap
```
public static long sizeOfMap(Map<?,?> map)
```
    Returns the size in bytes of a Map object, including sizes of its keys and values, supplying UNKNOWN_DEFAULT_RAM_BYTES_USED when object type is not well known. This method recurses up to MAX_DEPTH.
  - sizeOfMap
```
public static long sizeOfMap(Map<?,?> map,
                             long defSize)
```
    Returns the size in bytes of a Map object, including sizes of its keys and values, supplying default object size when object type is not well known. This method recurses up to MAX_DEPTH.
  - sizeOfCollection
```
public static long sizeOfCollection(Collection<?> collection)
```
    Returns the size in bytes of a Collection object, including sizes of its values, supplying UNKNOWN_DEFAULT_RAM_BYTES_USED when object type is not well known. This method recurses up to MAX_DEPTH.
  - sizeOfCollection
```
public static long sizeOfCollection(Collection<?> collection,
                                    long defSize)
```
    Returns the size in bytes of a Collection object, including sizes of its values, supplying default object size when object type is not well known. This method recurses up to MAX_DEPTH.
  - sizeOf
```
public static long sizeOf(Query q)
```
    Returns the size in bytes of a Query object. Unknown query types will be estimated as QUERY_DEFAULT_RAM_BYTES_USED.
  - sizeOf
```
public static long sizeOf(Query q,
                          long defSize)
```
    Returns the size in bytes of a Query object. Unknown query types will be estimated using shallowSizeOf(Object), or using the supplied defSize parameter if its value is greater than 0.
  - sizeOfObject
```
public static long sizeOfObject(Object o)
```
    Best effort attempt to estimate the size in bytes of an undetermined object. Known types will be estimated according to their formulas, and all other object sizes will be estimated as UNKNOWN_DEFAULT_RAM_BYTES_USED.
  - sizeOfObject
```
public static long sizeOfObject(Object o,
                                long defSize)
```
    Best effort attempt to estimate the size in bytes of an undetermined object. Known types will be estimated according to their formulas, and all other object sizes will be estimated using shallowSizeOf(Object), or using the supplied defSize parameter if its value is greater than 0.
  - sizeOf
```
public static long sizeOf(Accountable accountable)
```
    Returns the size in bytes of the Accountable object, using its Accountable.ramBytesUsed() method.
  - sizeOf
```
public static long sizeOf(String s)
```
    Returns the size in bytes of the String object.
  - shallowSizeOf
```
public static long shallowSizeOf(Object[] arr)
```
    Returns the shallow size in bytes of the Object[] object.
  - 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.
    
    See Also:
    
    shallowSizeOf(Object)
  - 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).
  - sizeOf
```
public static long sizeOf(Accountable[] accountables)
```
    Return the size of the provided array of Accountables by summing up the shallow size of the array and the memory usage reported by each Accountable.

Class RamUsageEstimator

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

ONE_KB

ONE_MB

ONE_GB

COMPRESSED_REFS_ENABLED

NUM_BYTES_OBJECT_REF

NUM_BYTES_OBJECT_HEADER

NUM_BYTES_ARRAY_HEADER

NUM_BYTES_OBJECT_ALIGNMENT

QUERY_DEFAULT_RAM_BYTES_USED

UNKNOWN_DEFAULT_RAM_BYTES_USED

primitiveSizes

HASHTABLE_RAM_BYTES_PER_ENTRY

LINKED_HASHTABLE_RAM_BYTES_PER_ENTRY

MAX_DEPTH

Method Detail

alignObjectSize

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOfMap

sizeOfMap

sizeOfCollection

sizeOfCollection

sizeOf

sizeOf

sizeOfObject

sizeOfObject

sizeOf

sizeOf

shallowSizeOf

shallowSizeOf

shallowSizeOfInstance

humanReadableUnits

humanReadableUnits

sizeOf