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https://issues.apache.org/jira/browse/HDFS-516?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12750246#action_12750246
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Jay Booth commented on HDFS-516:
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I did some benchmarking, here are the results:
Each test ran 1000 searches to warm, then 5000 searches to benchmark.
Binary search of a 20GB sorted sequence file of 20 million 1kb records.
Tests were run from the namenode in a 4-node EC2 medium cluster, 1.7 GB of ram
each. 1 namenode and 3 datanodes.
>From HDFS to a 512MB cached RadFS there was a 4X average improvement in search
>times, from 102ms to 24ms.
Each search was, theoretically, 24.25 reads (log 2 of 20 million). Not
actually measured.
I only ran each set once. The 90th percent line trends the right way, although
the max line is a little spikey. I'll add a 99th % in future benchmarks.
HDFS, baseline:
Warming with 1000 searches
Executed 5000 random searches with FS class
org.apache.hadoop.hdfs.DistributedFileSystem
Done, Search Times:
Mean: 102.17840000000015
Variance: 5939.660105461091
Median: 97.0
Max: 3095.0
Min: 33.0
90th pct: 130.0
Rad, no cache
Executed 5000 random searches with FS class
org.apache.hadoop.hdfs.rad.RadFileSystem
Done, Search Times:
Mean: 68.55640000000002
Variance: 233.8335857571515
Median: 67.0
Max: 379.0
Min: 26.0
90th pct: 79.0
Rad, 16MB cache:
Warming with 1000 searches
Executed 5000 random searches with FS class
org.apache.hadoop.hdfs.rad.RadFileSystem
Done, Search Times:
Mean: 42.039799999999985
Variance: 237.83818359671966
Median: 40.0
Max: 203.0
Min: 5.0
90th pct: 59.0
Rad, 128MB cache:
Warming with 1000 searches
Executed 5000 random searches with FS class
org.apache.hadoop.hdfs.rad.RadFileSystem
Done, Search Times:
Mean: 29.850600000000007
Variance: 202.08189601920367
Median: 27.0
Max: 203.0
Min: 1.0
90th pct: 45.0
Rad, 512MB cache:
Warming with 1000 searches
Executed 5000 random searches with FS class
org.apache.hadoop.hdfs.rad.RadFileSystem
Done, Search Times:
Mean: 24.274600000000014
Variance: 250.3052558911758
Median: 22.0
Max: 687.0
Min: 0.0
90th pct: 36.0
I could still shave a point or two by cleaning up my caching system to be more
graceful with its lookahead mechanism, but not bad for now. I'll pretty it up
and post a first attempt at a final patch soon.
> Low Latency distributed reads
> -----------------------------
>
> Key: HDFS-516
> URL: https://issues.apache.org/jira/browse/HDFS-516
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Jay Booth
> Priority: Minor
> Attachments: hdfs-516-20090824.patch, hdfs-516-20090831.patch,
> radfs.patch
>
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> I created a method for low latency random reads using NIO on the server side
> and simulated OS paging with LRU caching and lookahead on the client side.
> Some applications could include lucene searching (term->doc and doc->offset
> mappings are likely to be in local cache, thus much faster than nutch's
> current FsDirectory impl and binary search through record files (bytes at
> 1/2, 1/4, 1/8 marks are likely to be cached)
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