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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (IO-355) IOUtils read() and skip() methods are performance hogs
Date Wed, 31 Oct 2012 19:46:11 GMT

    [ https://issues.apache.org/jira/browse/IO-355?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13488154#comment-13488154
] 

Sebb commented on IO-355:
-------------------------

In the case of InputStream#skip(), the Javadoc says it throws:

bq. IOException - if the stream does not support seek or ...

so that might explain why the code uses read() rather than seek().
The Javadoc for Reader#skip() does not mention whether this is a possibility.
[The two classes have different authors, which may explain why Reader#skip throws IllegalArgumentException
for negative arg but InputStream#skip() does not]

An unconditional change to using skip from the implementation class could break some applications,
so this is not a trivial fix.
                
> IOUtils read() and skip() methods are performance hogs
> ------------------------------------------------------
>
>                 Key: IO-355
>                 URL: https://issues.apache.org/jira/browse/IO-355
>             Project: Commons IO
>          Issue Type: Bug
>          Components: Utilities
>    Affects Versions: 2.3, 2.4
>            Reporter: Uli Bubenheimer
>
> IOUtils.skip(InputStream, long) and IOUtils.skip(Reader, long) have the worst possible
performance as they always use read() on the input instead of using skip(). In many cases,
using skip() from a subclass of InputStream is much faster than read(), as the skip() can
be implemented via a disk seek.
> The IOUtils.skip() methods are used in the read() methods of IOUtils and their similarly
named siblings, so they tend to bring down the performance of all reads that involve a skip.
> Case in point: I have observed this performance degradation with Java 7 on Windows 7.
A series of consecutive reads on a large file on disk that involved skips changed my performance
from 30 secs as my baseline to 10 minutes after starting to use IOUtils.read().

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