The document discusses different types of block caches in HBase including LruBlockCache, SlabCache, and BucketCache. It explains that block caching improves performance by storing frequently accessed blocks in faster memory rather than slower disk storage. Each block cache has its own configuration options and memory usage characteristics. Benchmark results show that the off-heap BucketCache provides strong performance due to its use of off-heap memory for the L2 cache.

1. HBase
BlockCache
101
Nick
Dimiduk,
Hortonworks
@xefyr
n10k.com

2. Agenda
• What
is
a
BlockCache?
• Why
cache
blocks?
• Available
BlockCaches
• ConfiguraFons

3. RegionServer (HBase)
DataNode (Hadoop DFS)
HLog
(WAL)
HRegion
HStore
StoreFile
HFile
StoreFile
HFile
MemStore
...
...
HStore
BlockCache
HRegion
...
HStoreHStore
...
1 5
2
3
3
2
4
Read
Path
Refresher
BlockCache

4. What
is
a
block?
HFile
v2
Format
HFile
v2
format
figure
reproduced
from
MaMeo
Bertozzi,
"Apache
HBase
I/O
–
HFile”,
hMp://blog.cloudera.com/blog/2012/06/hbase-­‐io-­‐
hfile-­‐input-­‐output/

5. Why
cache
blocks?
Storage hierarchy: a different view
Dean/2009
Memory
is
100000x
faster
than
disk!
Disk
seek
=
10ms

6. LruBlockCache!
• On-­‐heap
ConcurrentHashMap!
• 3
block
prioriFes,
based
on
access
frequency
– Single
– MulF
– In-­‐memory
• Background
evicFon
thread
• HBASE-­‐1460,
0.20

7. LruBlockCache
ConfiguraFon
• Size
as
pct
of
heap
– hfile.block.cache.size
– default:
0.4
• Single
access
Priority
size
– hbase.lru.blockcache.single.percentage
– default:
0.25
• MulF-­‐access
priority
size
– hbase.lru.blockcache.multi.percentage
– default:
0.5
• In-­‐memory
priority
size
– hbase.lru.blockcache.memory.percentage
– default:
0.25

8. SlabCache!
• L2
cache;
fronted
by
LruBlockCache
(L1)
• DoubleBlockCache
caches
blocks
in
both
L1
and
L2
• Allocates
porFons
of
memory
with
target
block
size
• DirectByteBuffers
manage
off-­‐heap
memory
• Blocks
copied
on
and
off
heap
• HBASE-­‐4027,
0.92

9. SlabCache
ConfiguraFon
• SlabCache
size
– hbase.offheapcache.percentage!
• Target
Block
size
– hbase.offheapcache.minblocksize!
– default:
64k
• Slab
proporFons
– hbase.offheapcache.slab.proportions!
– default:
0.8,
0.2
• Slab
target
block
sizes
– hbase.offheapcache.slab.sizes!
– default:
64k,
128k

10. BucketCache!
• L2
cache;
fronted
by
LruBlockCache
(L1)
• CombinedBlockCache
caches
data
blocks
in
L2,
everything
else
in
L1
• Blocks
evicted
from
L1
are
promoted
to
L2
• Allocates
porFons
of
space
with
target
block
size
• Three
operaFng
modes:
– onheap
–
HeapByteBuffers
manage
on-­‐heap
memory
space
– offheap
–
DirectByteBuffers
manage
off-­‐heap
memory
space
– file
–
RandomAccessFile
manages
file-­‐backed
space
• Blocks
copied
on
and
off
heap
• HBASE-­‐7404,
0.96

11. BucketCache
ConfiguraFons
• OperaFng
mode
– hbase.bucketcache.ioengine!
• Total
cache
size
as
pct
of
heap
OR
size
in
MB:
– hbase.bucketcache.size!
• Size
of
L1
as
pct
of
total
cache
size:
– hbase.bucketcache.percentage.in.combinedcache!
– default:
0.9
• Target
Block
size
– hbase.offheapcache.minblocksize!
– default:
64k
• Bucket
target
block
sizes
– hbase.bucketcache.bucket.sizes!
– default:
14
sizes,
clustered
around
64k

12. BlockCache
Showdown
• Compare
performance:
– Total
cache
size
– Cache
size
vs.
Data
size
n10k.com/blog/
blockcache-­‐showdown/
L2
off-­‐heap
BucketCache
makes
a
strong
showing

13. Thanks!
M A N N I N G
Nick Dimiduk
Amandeep Khurana
FOREWORD BY
Michael Stack
hbaseinacFon.com
Nick
Dimiduk
github.com/ndimiduk
@xefyr
n10k.com
n10k.com/blog/blockcache-­‐101