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https://issues.apache.org/jira/browse/HDFS-4461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13687130#comment-13687130
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Todd Lipcon commented on HDFS-4461:
-----------------------------------
todd@todd-w510:~$ cat /tmp/c
A few quick comments on the patch:
{code}
+ return path.replaceAll("(?<!^)(\\\\|/){2,}",
+ Matcher.quoteReplacement(File.separator));
{code}
Can you introduce a constant {{Pattern}} instance for this regex? That way
you'll avoid the overhead of recompiling the regex each time this is called.
--
- Can you add comments to the {{blockSuffix}} and {{metaSuffix}} members about
their behavior when null? If I understand correctly, it would be something like:
{code}
/**
* The block file path, relative to the volume's base directory.
* If there was no block file found, this may be null. If 'vol'
* is null, then this is the full path of the block file.
*/
private final String blockSuffix;
/**
* The suffix of the meta file path relative to the block file.
* If blockSuffix is null, then this will be the entire path relative
* to the volume base directory, or an absolute path if vol is also
* null.
*/
private final String metaSuffix;
{code}
- Maybe add a simple unit test for ScanInfo to test the various combinations,
making sure that you get back the same paths that you put in?
> DirectoryScanner: volume path prefix takes up memory for every block that is
> scanned
> -------------------------------------------------------------------------------------
>
> Key: HDFS-4461
> URL: https://issues.apache.org/jira/browse/HDFS-4461
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.0.3-alpha
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
> Priority: Minor
> Attachments: HDFS-4461.002.patch, HDFS-4461.003.patch,
> HDFS-4461.004.patch, memory-analysis.png
>
>
> In the {{DirectoryScanner}}, we create a class {{ScanInfo}} for every block.
> This object contains two File objects-- one for the metadata file, and one
> for the block file. Since those File objects contain full paths, users who
> pick a lengthly path for their volume roots will end up using an extra
> N_blocks * path_prefix bytes per block scanned. We also don't really need to
> store File objects-- storing strings and then creating File objects as needed
> would be cheaper. This would be a nice efficiency improvement.
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