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From "Xiaoyu Yao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10690) Optimize insertion/removal of replica in ShortCircuitCache.java
Date Fri, 30 Sep 2016 18:26:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10690?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15536651#comment-15536651

Xiaoyu Yao commented on HDFS-10690:

[~fenghua_hu], we will need to update {{TestEnhancedByteBufferAccess.java}} and {{TestShortCircuitCache.java}}
now that the {{CacheVisitor}} interface has been changed. Otherwise, it will fail with compiler
error like below. 

Not sure why Jenkins run did not catch this, but will file separate infra JIRA for that. 

[ERROR] /hadoop/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/fs/TestEnhancedByteBufferAccess.java:[291,18]
org.apache.hadoop.fs.TestEnhancedByteBufferAccess.CountingVisitor is not abstract and does
not override abstract method visit(int,java.util.Map<org.apache.hadoop.hdfs.ExtendedBlockId,org.apache.hadoop.hdfs.shortcircuit.ShortCircuitReplica>,java.util.Map<org.apache.hadoop.hdfs.ExtendedBlockId,org.apache.hadoop.security.token.SecretManager.InvalidToken>,org.apache.commons.collections.map.LinkedMap,org.apache.commons.collections.map.LinkedMap)
in org.apache.hadoop.hdfs.shortcircuit.ShortCircuitCache.CacheVisitor
[ERROR] /hadoop/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/fs/TestEnhancedByteBufferAccess.java:[306,5]
method does not override or implement a method from a supertype

> Optimize insertion/removal of replica in ShortCircuitCache.java
> ---------------------------------------------------------------
>                 Key: HDFS-10690
>                 URL: https://issues.apache.org/jira/browse/HDFS-10690
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 3.0.0-alpha2
>            Reporter: Fenghua Hu
>            Assignee: Fenghua Hu
>         Attachments: HDFS-10690.001.patch, HDFS-10690.002.patch, HDFS-10690.003.patch,
HDFS-10690.004.patch, HDFS-10690.005.patch, HDFS-10690.006.patch, ShortCircuitCache_LinkedMap.patch
>   Original Estimate: 336h
>  Remaining Estimate: 336h
> Currently in ShortCircuitCache, two TreeMap objects are used to track the cached replicas.
> private final TreeMap<Long, ShortCircuitReplica> evictable = new TreeMap<>();
> private final TreeMap<Long, ShortCircuitReplica> evictableMmapped = new TreeMap<>();
> TreeMap employs Red-Black tree for sorting. This isn't an issue when using traditional
HDD. But when using high-performance SSD/PCIe Flash, the cost inserting/removing an entry
 becomes considerable.
> To mitigate it, we designed a new list-based for replica tracking.
> The list is a double-linked FIFO. FIFO is time-based, thus insertion is a very low cost
operation. On the other hand, list is not lookup-friendly. To address this issue, we introduce
two references into ShortCircuitReplica object.
> ShortCircuitReplica next = null;
> ShortCircuitReplica prev = null;
> In this way, lookup is not needed when removing a replica from the list. We only need
to modify its predecessor's and successor's references in the lists.
> Our tests showed up to 15-50% performance improvement when using PCIe flash as storage
> The original patch is against 2.6.4, now I am porting to Hadoop trunk, and patch will
be posted soon.

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