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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8859) Improve DataNode (ReplicaMap) memory footprint to save about 45%
Date Wed, 12 Aug 2015 11:35:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14693340#comment-14693340
] 

Hadoop QA commented on HDFS-8859:
---------------------------------

\\
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:red}-1{color} | pre-patch |  17m  2s | Findbugs (version ) appears to be broken on
trunk. |
| {color:green}+1{color} | @author |   0m  0s | The patch does not contain any @author tags.
|
| {color:green}+1{color} | tests included |   0m  0s | The patch appears to include 3 new
or modified test files. |
| {color:green}+1{color} | javac |   7m 44s | There were no new javac warning messages. |
| {color:green}+1{color} | javadoc |   9m 38s | There were no new javadoc warning messages.
|
| {color:green}+1{color} | release audit |   0m 22s | The applied patch does not increase
the total number of release audit warnings. |
| {color:red}-1{color} | checkstyle |   1m 29s | The applied patch generated  6 new checkstyle
issues (total was 12, now 14). |
| {color:red}-1{color} | whitespace |   0m  1s | The patch has 3  line(s) that end in whitespace.
Use git apply --whitespace=fix. |
| {color:green}+1{color} | install |   1m 29s | mvn install still works. |
| {color:green}+1{color} | eclipse:eclipse |   0m 32s | The patch built with eclipse:eclipse.
|
| {color:green}+1{color} | findbugs |   4m 25s | The patch does not introduce any new Findbugs
(version 3.0.0) warnings. |
| {color:red}-1{color} | common tests |  22m 16s | Tests failed in hadoop-common. |
| {color:red}-1{color} | hdfs tests | 220m 50s | Tests failed in hadoop-hdfs. |
| | | 286m  7s | |
\\
\\
|| Reason || Tests ||
| Failed unit tests | hadoop.ha.TestZKFailoverController |
|   | hadoop.net.TestNetUtils |
|   | hadoop.hdfs.server.namenode.ha.TestDNFencing |
|   | hadoop.hdfs.server.namenode.snapshot.TestSnapshot |
| Timed out tests | org.apache.hadoop.hdfs.server.namenode.TestParallelImageWrite |
|   | org.apache.hadoop.hdfs.server.namenode.TestFsck |
|   | org.apache.hadoop.hdfs.TestRestartDFS |
|   | org.apache.hadoop.cli.TestHDFSCLI |
\\
\\
|| Subsystem || Report/Notes ||
| Patch URL | http://issues.apache.org/jira/secure/attachment/12750016/HDFS-8859.003.patch
|
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / 1ea1a83 |
| checkstyle |  https://builds.apache.org/job/PreCommit-HDFS-Build/11976/artifact/patchprocess/diffcheckstylehadoop-common.txt
|
| whitespace | https://builds.apache.org/job/PreCommit-HDFS-Build/11976/artifact/patchprocess/whitespace.txt
|
| hadoop-common test log | https://builds.apache.org/job/PreCommit-HDFS-Build/11976/artifact/patchprocess/testrun_hadoop-common.txt
|
| hadoop-hdfs test log | https://builds.apache.org/job/PreCommit-HDFS-Build/11976/artifact/patchprocess/testrun_hadoop-hdfs.txt
|
| Test Results | https://builds.apache.org/job/PreCommit-HDFS-Build/11976/testReport/ |
| Java | 1.7.0_55 |
| uname | Linux asf909.gq1.ygridcore.net 3.13.0-36-lowlatency #63-Ubuntu SMP PREEMPT Wed Sep
3 21:56:12 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux |
| Console output | https://builds.apache.org/job/PreCommit-HDFS-Build/11976/console |


This message was automatically generated.

> Improve DataNode (ReplicaMap) memory footprint to save about 45%
> ----------------------------------------------------------------
>
>                 Key: HDFS-8859
>                 URL: https://issues.apache.org/jira/browse/HDFS-8859
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>            Reporter: Yi Liu
>            Assignee: Yi Liu
>            Priority: Critical
>         Attachments: HDFS-8859.001.patch, HDFS-8859.002.patch, HDFS-8859.003.patch
>
>
> By using following approach we can save about *45%* memory footprint for each block replica
in DataNode memory (This JIRA only talks about *ReplicaMap* in DataNode), the details are:
> In ReplicaMap, 
> {code}
> private final Map<String, Map<Long, ReplicaInfo>> map =
>     new HashMap<String, Map<Long, ReplicaInfo>>();
> {code}
> Currently we use a HashMap {{Map<Long, ReplicaInfo>}} to store the replicas in
memory.  The key is block id of the block replica which is already included in {{ReplicaInfo}},
so this memory can be saved.  Also HashMap Entry has a object overhead.  We can implement
a lightweight Set which is  similar to {{LightWeightGSet}}, but not a fixed size ({{LightWeightGSet}}
uses fix size for the entries array, usually it's a big value, an example is {{BlocksMap}},
this can avoid full gc since no need to resize),  also we should be able to get Element through
key.
> Following is comparison of memory footprint If we implement a lightweight set as described:
> We can save:
> {noformat}
>     SIZE (bytes)           ITEM
>     20                        The Key: Long (12 bytes object overhead + 8 bytes long)
>     12                        HashMap Entry object overhead
>     4                          reference to the key in Entry
>     4                          reference to the value in Entry
>     4                          hash in Entry
> {noformat}
> Total:  -44 bytes
> We need to add:
> {noformat}
>     SIZE (bytes)           ITEM
>     4                             a reference to next element in ReplicaInfo
> {noformat}
> Total:  +4 bytes
> So totally we can save 40bytes for each block replica 
> And currently one finalized replica needs around 46 bytes (notice: we ignore memory alignment
here).
> We can save 1 - (4 + 46) / (44 + 46) = *45%*  memory for each block replica in DataNode.
>     



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