BucketEntry (Apache HBase 2.3.0 API)

java.lang.Object
- org.apache.hadoop.hbase.io.hfile.bucket.BucketEntry

All Implemented Interfaces:

HBaseReferenceCounted, org.apache.hbase.thirdparty.io.netty.util.ReferenceCounted
```
@InterfaceAudience.Private
class BucketEntry
extends Object
implements HBaseReferenceCounted
```
Item in cache. We expect this to be where most memory goes. Java uses 8 bytes just for object headers; after this, we want to use as little as possible - so we only use 8 bytes, but in order to do so we end up messing around with all this Java casting stuff. Offset stored as 5 bytes that make up the long. Doubt we'll see devices this big for ages. Offsets are divided by 256. So 5 bytes gives us 256TB or so.

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

(package private) static interface BucketEntry.BucketEntryHandler<T>

Nested Classes
Modifier and Type	Class and Description
`(package private) static interface`	`BucketEntry.BucketEntryHandler<T>`

Field Summary

Fields
Modifier and Type	Field and Description
`private long`	`accessCounter`
`(package private) ByteBuffAllocator`	`allocator`
`private long`	`cachedTime` Time this block was cached.
`(package private) static Comparator<BucketEntry>`	`COMPARATOR`
`(package private) byte`	`deserializerIndex` The index of the deserializer that can deserialize this BucketEntry content.
`private int`	`length`
`(package private) AtomicBoolean`	`markedAsEvicted`
`private byte`	`offset1`
`private int`	`offsetBase`
`private BlockPriority`	`priority`
`private RefCnt`	`refCnt` The RefCnt means how many paths are referring the `BucketEntry`, each RPC reading path is considering as one path, the `BucketCache.backingMap` reference is also considered a path.

Constructor Summary

Constructors
Constructor and Description
`BucketEntry(long offset, int length, long accessCounter, boolean inMemory)`
`BucketEntry(long offset, int length, long accessCounter, boolean inMemory, RefCnt refCnt, ByteBuffAllocator allocator)`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`(package private) void`	`access(long accessCounter)` Block has been accessed.
`(package private) CacheableDeserializer<Cacheable>`	`deserializerReference()`
`(package private) long`	`getAccessCounter()`
`(package private) long`	`getCachedTime()`
`int`	`getLength()`
`BlockPriority`	`getPriority()`
`(package private) boolean`	`isRpcRef()` Check whether have some RPC patch referring this block.
`(package private) boolean`	`markAsEvicted()` The `BucketCache` will try to release its reference to this BucketEntry many times.
`(package private) boolean`	`markStaleAsEvicted()` Mark as evicted only when NO RPC references.
`(package private) long`	`offset()`
`int`	`refCnt()`
`boolean`	`release()` We've three cases to release refCnt now: 1.
`BucketEntry`	`retain()`
`(package private) void`	`setDeserializerReference(CacheableDeserializer<Cacheable> deserializer)`
`private void`	`setOffset(long value)`
`(package private) <T> T`	`withWriteLock(IdReadWriteLock<Long> offsetLock, BucketEntry.BucketEntryHandler<T> handler)`
`(package private) Cacheable`	`wrapAsCacheable(ByteBuff buf)`
`(package private) Cacheable`	`wrapAsCacheable(ByteBuffer[] buffers)`

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

Methods inherited from interface org.apache.hadoop.hbase.nio.HBaseReferenceCounted
release, retain, touch, touch

- Field Detail
  - COMPARATOR
```
static final Comparator<BucketEntry> COMPARATOR
```
  - offsetBase
```
private int offsetBase
```
  - length
```
private int length
```
  - offset1
```
private byte offset1
```
  - deserializerIndex
```
byte deserializerIndex
```
    The index of the deserializer that can deserialize this BucketEntry content. See CacheableDeserializerIdManager for hosting of index to serializers.
  - accessCounter
```
private volatile long accessCounter
```
  - priority
```
private BlockPriority priority
```
  - refCnt
```
private final RefCnt refCnt
```
    The RefCnt means how many paths are referring the BucketEntry, each RPC reading path is considering as one path, the BucketCache.backingMap reference is also considered a path. NOTICE that if two read RPC path hit the same BucketEntry, then the HFileBlocks the two RPC referred will share the same refCnt instance with the BucketEntry. so the refCnt will increase or decrease as the following:
    1. when writerThread flush the block into IOEngine and add the bucketEntry into backingMap, the refCnt ++;
    2. If BucketCache evict the block and move the bucketEntry out of backingMap, the refCnt--; it usually happen when HFile is closing or someone call the clearBucketCache by force.
    3. The read RPC path start to refer the block which is backend by the memory area in bucketEntry, then refCnt ++ ;
    4. The read RPC patch shipped the response, and release the block. then refCnt--;
    Once the refCnt decrease to zero, then the BucketAllocator will free the block area.
  - markedAsEvicted
```
final AtomicBoolean markedAsEvicted
```
  - allocator
```
final ByteBuffAllocator allocator
```
  - cachedTime
```
private final long cachedTime
```
    Time this block was cached. Presumes we are created just before we are added to the cache.
- Constructor Detail
  - BucketEntry
```
BucketEntry(long offset,
            int length,
            long accessCounter,
            boolean inMemory)
```
  - BucketEntry
```
BucketEntry(long offset,
            int length,
            long accessCounter,
            boolean inMemory,
            RefCnt refCnt,
            ByteBuffAllocator allocator)
```
- Method Detail
  - offset
```
long offset()
```
  - setOffset
```
private void setOffset(long value)
```
  - getLength
```
public int getLength()
```
  - deserializerReference
```
CacheableDeserializer<Cacheable> deserializerReference()
```
  - setDeserializerReference
```
void setDeserializerReference(CacheableDeserializer<Cacheable> deserializer)
```
  - getAccessCounter
```
long getAccessCounter()
```
  - access
```
void access(long accessCounter)
```
    Block has been accessed. Update its local access counter.
  - getPriority
```
public BlockPriority getPriority()
```
  - getCachedTime
```
long getCachedTime()
```
  - markAsEvicted
```
boolean markAsEvicted()
```
    The BucketCache will try to release its reference to this BucketEntry many times. we must make sure the idempotent, otherwise it'll decrease the RPC's reference count in advance, then for RPC memory leak happen.
    
    Returns:
    
    true if we deallocate this entry successfully.
  - markStaleAsEvicted
```
boolean markStaleAsEvicted()
```
    Mark as evicted only when NO RPC references. Mainly used for eviction when cache size exceed the max acceptable size.
    
    Returns:
    
    true if we deallocate this entry successfully.
  - isRpcRef
```
boolean isRpcRef()
```
    Check whether have some RPC patch referring this block. There're two case:
    1. If current refCnt is greater than 1, there must be at least one referring RPC path;
    2. If current refCnt is equal to 1 and the markedAtEvicted is true, the it means backingMap has released its reference, the remaining reference can only be from RPC path.
    We use this check to decide whether we can free the block area: when cached size exceed the acceptable size, our eviction policy will choose those stale blocks without any RPC reference and the RPC referred block will be excluded.
    
    Returns:
    
    true to indicate there're some RPC referring the block.
  - wrapAsCacheable
```
Cacheable wrapAsCacheable(ByteBuffer[] buffers)
                   throws IOException
```
    Throws:
    
    IOException
  - wrapAsCacheable
```
Cacheable wrapAsCacheable(ByteBuff buf)
                   throws IOException
```
    Throws:
    
    IOException
  - withWriteLock
```
<T> T withWriteLock(IdReadWriteLock<Long> offsetLock,
                    BucketEntry.BucketEntryHandler<T> handler)
```
  - refCnt
```
public int refCnt()
```
    Specified by:
    
    refCnt in interface org.apache.hbase.thirdparty.io.netty.util.ReferenceCounted
  - retain
```
public BucketEntry retain()
```
    Specified by:
    
    retain in interface org.apache.hbase.thirdparty.io.netty.util.ReferenceCounted
  - release
```
public boolean release()
```
    We've three cases to release refCnt now:
    1. BucketCache#evictBlock, it will release the backingMap's reference by force because we're closing file or clear the bucket cache or some corruption happen. when all rpc references gone, then free the area in bucketAllocator.
    2. BucketCache#returnBlock . when rpc shipped, we'll release the block, only when backingMap also release its refCnt (case.1 will do this) and no other rpc reference, then it will free the area in bucketAllocator.
    3.evict those block without any rpc reference if cache size exceeded. we'll only free those blocks with zero rpc reference count, as the markStaleAsEvicted() do.
    
    Specified by:
    
    release in interface org.apache.hbase.thirdparty.io.netty.util.ReferenceCounted
    
    Returns:
    
    true to indicate we've decreased to zero and do the de-allocation.

Class BucketEntry

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface org.apache.hadoop.hbase.nio.HBaseReferenceCounted

Field Detail

COMPARATOR

offsetBase

length

offset1

deserializerIndex

accessCounter

priority

refCnt

markedAsEvicted

allocator

cachedTime

Constructor Detail

BucketEntry

BucketEntry

Method Detail

offset

setOffset

getLength

deserializerReference

setDeserializerReference

getAccessCounter

access

getPriority

getCachedTime

markAsEvicted

markStaleAsEvicted

isRpcRef

wrapAsCacheable

wrapAsCacheable

withWriteLock

refCnt

retain

release