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From Jan Schellenberger <leipz...@gmail.com>
Subject Slow Get Performance (or how many disk I/O does it take for one non-cached read?)
Date Fri, 31 Jan 2014 23:12:09 GMT
I am running a cluster and getting slow performance - about 50 reads/sec/node
or about 800 reads/sec for the cluster.  The data is too big to fit into
memory and my access pattern is completely random reads which is presumably
difficult for hbase.  Is my read speed reasonable?  I feel like typical read
speeds I've seen reported are much higher?



Hardware/Software Configuration:
17 nodes + 1 master
8 cores
24 gigs ram
4x1TB 3.5" hard drives (I know this is low for hbase - we're working on
getting more disks)
running Cloudera CDH 4.3 with hbase .94.6
Most configurations are default except I'm using 12GB heap space/region
server and the block cache is .4 instead of .25 but neither of these two
things makes much of a difference.   I am NOT having a GC issue.  Latencies
are around 40ms and 99% is 200ms. 


Dataset Description:
6 tables ~300GB each (uncompressed) or 120GB each compressed <- compression
speeds things up a bit.
I just ran a major compaction so block locality is 100%
Each Table has a single column family and a single column ("c:d").  
keys are short strigs ~10-20 characters.
values are short json ~500 characters
100% Gets.  No Puts
I am heavily using time stamping.  maxversions is set to Integer.MAXINT.  My
gets have a maxretrieved of 200.  A typical row would have < 10 versions on
average though.  <1% of queries would max out at 200 versions returned.

Here are table configurations (I've also tried Snappy compression)
{NAME => 'TABLE1', FAMILIES => [{NAME => 'c', DATA_BLOCK_ENCODING => 'NONE'
 , BLOOMFILTER => 'ROW', REPLICATION_SCOPE => '0', VERSIONS => '2147483647',
COMPR
 ESSION => 'NONE', MIN_VERSIONS => '0', TTL => '2147483647',
KEEP_DELETED_CELLS =>
  'false', BLOCKSIZE => '65536', IN_MEMORY => 'false', ENCODE_ON_DISK =>
'true', BLOCKCACHE => 'true'}]}


I am using the master node to query (with 20 threads) and get about 800
Gets/second.  Each worker node is completely swamped by disk i/o - I'm
seeing 80 io/sec with iostat for each of the 4 disk with a throughput of
about 10MB/sec each.  So this means it's reading roughly 120kB/transfer and
it's taking about 8 Hard Disk I/O's per Get request.  Does that seem
reasonable?  I've read the HFILE specs and I feel if the block index is
loaded into memory, it should take 1 hard disk read to read the proper block
with my row.


The region servers have a blockCacheHitRatio of about 33% (no compression)
or 50% (snappy compression)

Here are some regionserver stats while I'm running queries.  This is the
uncompressed table version and queries are only 38/sec
 
requestsPerSecond=38, numberOfOnlineRegions=212,
 numberOfStores=212, numberOfStorefiles=212, storefileIndexSizeMB=0,
rootIndexSizeKB=190, totalStaticIndexSizeKB=172689,
totalStaticBloomSizeKB=79692, memstoreSizeMB=0, mbInMemoryWithoutWAL=0,
numberOfPutsWithoutWAL=0, readRequestsCount=1865459,
writeRequestsCount=0, compactionQueueSize=0, flushQueueSize=0,
usedHeapMB=4565, maxHeapMB=12221, blockCacheSizeMB=4042.53,
blockCacheFreeMB=846.07, blockCacheCount=62176,
blockCacheHitCount=5389770, blockCacheMissCount=9909385,
blockCacheEvictedCount=2744919, blockCacheHitRatio=35%,
blockCacheHitCachingRatio=65%, hdfsBlocksLocalityIndex=99,
slowHLogAppendCount=0, fsReadLatencyHistogramMean=1570049.34,
fsReadLatencyHistogramCount=1239690.00,
fsReadLatencyHistogramMedian=20859045.50,
fsReadLatencyHistogram75th=35791318.75,
fsReadLatencyHistogram95th=97093132.05,
fsReadLatencyHistogram99th=179688655.93,
fsReadLatencyHistogram999th=312277183.40,
fsPreadLatencyHistogramMean=35548585.63,
fsPreadLatencyHistogramCount=2803268.00,
fsPreadLatencyHistogramMedian=37662144.00,
fsPreadLatencyHistogram75th=55991186.50,
fsPreadLatencyHistogram95th=116227275.50,
fsPreadLatencyHistogram99th=173173999.27,
fsPreadLatencyHistogram999th=273812341.79,
fsWriteLatencyHistogramMean=1523660.72,
fsWriteLatencyHistogramCount=1225000.00,
fsWriteLatencyHistogramMedian=226540.50,
fsWriteLatencyHistogram75th=380366.00,
fsWriteLatencyHistogram95th=2193516.80,
fsWriteLatencyHistogram99th=4290208.93,
fsWriteLatencyHistogram999th=6926850.53









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