org.apache.flink.runtime.memory

Class MemoryManager

java.lang.Object

org.apache.flink.runtime.memory.MemoryManager

public class MemoryManager
extends Object

The memory manager governs the memory that Flink uses for sorting, hashing, and caching. Memory is represented in segments of equal size. Operators allocate the memory by requesting a number of memory segments.

The memory may be represented as on-heap byte arrays (HeapMemorySegment), or as off-heap memory regions (HybridMemorySegment). Which kind of memory the MemoryManager serves can be passed as an argument to the initialization.

The memory manager can either pre-allocate all memory, or allocate the memory on demand. In the former version, memory will be occupied and reserved from start on, which means that no OutOfMemoryError can come while requesting memory. Released memory will also return to the MemoryManager's pool. On-demand allocation means that the memory manager only keeps track how many memory segments are currently allocated (bookkeeping only). Releasing a memory segment will not add it back to the pool, but make it re-claimable by the garbage collector.

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_PAGE_SIZE The default memory page size.
static int	MIN_PAGE_SIZE The minimal memory page size.

Constructor Summary

Constructors

Constructor and Description
MemoryManager(long memorySize, int numberOfSlots) Creates a memory manager with the given capacity, using the default page size.
MemoryManager(long memorySize, int numberOfSlots, int pageSize, MemoryType memoryType, boolean preAllocateMemory) Creates a memory manager with the given capacity and given page size.

Method Summary

Modifier and Type	Method and Description
List<MemorySegment>	allocatePages(Object owner, int numPages) Allocates a set of memory segments from this memory manager.
void	allocatePages(Object owner, List<MemorySegment> target, int numPages) Allocates a set of memory segments from this memory manager.
long	computeMemorySize(double fraction) Computes the memory size of the fraction per slot.
int	computeNumberOfPages(double fraction) Computes to how many pages the given number of bytes corresponds.
long	getMemorySize() Returns the total size of memory handled by this memory manager.
MemoryType	getMemoryType() Gets the type of memory (heap / off-heap) managed by this memory manager.
int	getPageSize() Gets the size of the pages handled by the memory manager.
int	getTotalNumPages() Gets the total number of memory pages managed by this memory manager.
boolean	isPreAllocated() Checks whether this memory manager pre-allocates the memory.
boolean	isShutdown() Checks whether the MemoryManager has been shut down.
void	release(Collection<MemorySegment> segments) Tries to release many memory segments together.
void	release(MemorySegment segment) Tries to release the memory for the specified segment.
void	releaseAll(Object owner) Releases all memory segments for the given owner.
long	roundDownToPageSizeMultiple(long numBytes) Rounds the given value down to a multiple of the memory manager's page size.
void	shutdown() Shuts the memory manager down, trying to release all the memory it managed.
boolean	verifyEmpty() Checks if the memory manager all memory available.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_PAGE_SIZE

public static final int DEFAULT_PAGE_SIZE

The default memory page size. Currently set to 32 KiBytes.

See Also:

Constant Field Values

MIN_PAGE_SIZE

public static final int MIN_PAGE_SIZE

The minimal memory page size. Currently set to 4 KiBytes.

See Also:

Constant Field Values

Constructor Detail

MemoryManager

public MemoryManager(long memorySize,
                     int numberOfSlots)

Creates a memory manager with the given capacity, using the default page size.

Parameters:

memorySize - The total size of the memory to be managed by this memory manager.

numberOfSlots - The number of slots of the task manager.

MemoryManager

public MemoryManager(long memorySize,
                     int numberOfSlots,
                     int pageSize,
                     MemoryType memoryType,
                     boolean preAllocateMemory)

Creates a memory manager with the given capacity and given page size.

Parameters:

memorySize - The total size of the memory to be managed by this memory manager.

numberOfSlots - The number of slots of the task manager.

pageSize - The size of the pages handed out by the memory manager.

memoryType - The type of memory (heap / off-heap) that the memory manager should allocate.

preAllocateMemory - True, if the memory manager should immediately allocate all memory, false if it should allocate and release the memory as needed.

Method Detail

shutdown

public void shutdown()

Shuts the memory manager down, trying to release all the memory it managed. Depending on implementation details, the memory does not necessarily become reclaimable by the garbage collector, because there might still be references to allocated segments in the code that allocated them from the memory manager.

isShutdown

public boolean isShutdown()

Checks whether the MemoryManager has been shut down.

Returns:

True, if the memory manager is shut down, false otherwise.

verifyEmpty

public boolean verifyEmpty()

Checks if the memory manager all memory available.

Returns:

True, if the memory manager is empty and valid, false if it is not empty or corrupted.

allocatePages

public List<MemorySegment> allocatePages(Object owner,
                                         int numPages)
                                  throws MemoryAllocationException

Allocates a set of memory segments from this memory manager. If the memory manager pre-allocated the segments, they will be taken from the pool of memory segments. Otherwise, they will be allocated as part of this call.

Parameters:

owner - The owner to associate with the memory segment, for the fallback release.

numPages - The number of pages to allocate.

Returns:

A list with the memory segments.

Throws:

MemoryAllocationException - Thrown, if this memory manager does not have the requested amount of memory pages any more.

allocatePages

public void allocatePages(Object owner,
                          List<MemorySegment> target,
                          int numPages)
                   throws MemoryAllocationException

Allocates a set of memory segments from this memory manager. If the memory manager pre-allocated the segments, they will be taken from the pool of memory segments. Otherwise, they will be allocated as part of this call.

Parameters:

owner - The owner to associate with the memory segment, for the fallback release.

target - The list into which to put the allocated memory pages.

numPages - The number of pages to allocate.

Throws:

MemoryAllocationException - Thrown, if this memory manager does not have the requested amount of memory pages any more.

release

public void release(MemorySegment segment)

Tries to release the memory for the specified segment. If the segment has already been released or is null, the request is simply ignored.

If the memory manager manages pre-allocated memory, the memory segment goes back to the memory pool. Otherwise, the segment is only freed and made eligible for reclamation by the GC.

Parameters:

segment - The segment to be released.

Throws:

IllegalArgumentException - Thrown, if the given segment is of an incompatible type.

release

public void release(Collection<MemorySegment> segments)

Tries to release many memory segments together.

If the memory manager manages pre-allocated memory, the memory segment goes back to the memory pool. Otherwise, the segment is only freed and made eligible for reclamation by the GC.

Parameters:

segments - The segments to be released.

Throws:

NullPointerException - Thrown, if the given collection is null.

IllegalArgumentException - Thrown, id the segments are of an incompatible type.

releaseAll

public void releaseAll(Object owner)

Releases all memory segments for the given owner.

Parameters:

owner - The owner memory segments are to be released.

getMemoryType

public MemoryType getMemoryType()

Gets the type of memory (heap / off-heap) managed by this memory manager.

Returns:

The type of memory managed by this memory manager.

isPreAllocated

public boolean isPreAllocated()

Checks whether this memory manager pre-allocates the memory.

Returns:

True if the memory manager pre-allocates the memory, false if it allocates as needed.

getPageSize

public int getPageSize()

Gets the size of the pages handled by the memory manager.

Returns:

The size of the pages handled by the memory manager.

getMemorySize

public long getMemorySize()

Returns the total size of memory handled by this memory manager.

Returns:

The total size of memory.

getTotalNumPages

public int getTotalNumPages()

Gets the total number of memory pages managed by this memory manager.

Returns:

The total number of memory pages managed by this memory manager.

computeNumberOfPages

public int computeNumberOfPages(double fraction)

Computes to how many pages the given number of bytes corresponds. If the given number of bytes is not an exact multiple of a page size, the result is rounded down, such that a portion of the memory (smaller than the page size) is not included.

Parameters:

fraction - the fraction of the total memory per slot

Returns:

The number of pages to which

computeMemorySize

public long computeMemorySize(double fraction)

Computes the memory size of the fraction per slot.

Parameters:

fraction - The fraction of the memory of the task slot.

Returns:

The number of pages corresponding to the memory fraction.

roundDownToPageSizeMultiple

public long roundDownToPageSizeMultiple(long numBytes)

Rounds the given value down to a multiple of the memory manager's page size.

Returns:

The given value, rounded down to a multiple of the page size.