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https://issues.apache.org/jira/browse/HADOOP-15245?focusedWorklogId=742508&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-742508
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ASF GitHub Bot logged work on HADOOP-15245:
-------------------------------------------
Author: ASF GitHub Bot
Created on: 16/Mar/22 16:36
Start Date: 16/Mar/22 16:36
Worklog Time Spent: 10m
Work Description: ahmarsuhail commented on a change in pull request #3927:
URL: https://github.com/apache/hadoop/pull/3927#discussion_r828203561
##########
File path:
hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AInputStream.java
##########
@@ -781,6 +781,46 @@ public void readFully(long position, byte[] buffer, int
offset, int length)
}
}
+ /**
+ * {@inheritDoc}
+ *
+ * This implements a more efficient method for skip. It calls lazy seek
+ * which will either make a new get request or do a default skip.
+ * If lazy seek fails, try doing a default skip.
+ *
+ * @param n Number of bytes to be skipped
+ * @return Number of bytes skipped
+ * @throws IOException on any problem
+ */
+ @Override
+ @Retries.OnceTranslated
+ public long skip(final long n) throws IOException {
+
+ if (n <= 0) {
+ return 0;
+ }
+
+ checkNotClosed();
+ streamStatistics.skipOperationStarted();
+
+ long targetPos = pos + n;
Review comment:
After implementing the test, I realised that `read()` uses the
`nextReadPos` to get the byte. To get the correct byte after a skip, we need to
update nextReadPos too. We can just do this inside the `skip()` method and
don't need to update it in the places I mentioned above.
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Issue Time Tracking
-------------------
Worklog Id: (was: 742508)
Time Spent: 3.5h (was: 3h 20m)
> S3AInputStream.skip() to use lazy seek
> --------------------------------------
>
> Key: HADOOP-15245
> URL: https://issues.apache.org/jira/browse/HADOOP-15245
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.1.0
> Reporter: Steve Loughran
> Priority: Major
> Labels: pull-request-available
> Time Spent: 3.5h
> Remaining Estimate: 0h
>
> the default skip() does a read and discard of all bytes, no matter how far
> ahead the skip is. This is very inefficient if the skip() is being done on
> S3A random IO, though exactly what to do when in sequential mode.
> Proposed:
> * add an optimized version of S3AInputStream.skip() which does a lazy seek,
> which itself will decided when to skip() vs issue a new GET.
> * add some more instrumentation to measure how often this gets used
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