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https://issues.apache.org/jira/browse/HADOOP-18296?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18007927#comment-18007927
]
ASF GitHub Bot commented on HADOOP-18296:
-----------------------------------------
mukund-thakur commented on code in PR #7732:
URL: https://github.com/apache/hadoop/pull/7732#discussion_r2214416106
##########
hadoop-common-project/hadoop-common/src/main/resources/core-default.xml:
##########
@@ -1364,6 +1364,24 @@
<description>File space usage statistics refresh interval in
msec.</description>
</property>
+<property>
+ <name>fs.file.checksum.verify</name>
+ <value>true</value>
+ <description>
+ Should data read through the local filesystem (file://) URLs be verified
aginst
+ the checksums stored in the associated checksum files?
+ Setting this to false skips loading the checksum files, reading data in
checksum-aligned
+ blocks and verifying checksums. This may improve performance
+ when reading data, though it pushes the responsibility of detecting errors
+ into the file formats themselves, or the underlying storage system.
+ Even when verification is enabled, files without associated checksum files
+ .$FILENAME.crc are never be verified.
+ When fs.file.checksum.verify is false, vector reads of date will always
return
Review Comment:
typo : date to data
##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ChecksumFileSystem.java:
##########
@@ -489,9 +512,27 @@ public void readVectored(final List<? extends FileRange>
ranges,
}
}
+ private boolean delegateVectorReadsToInner() {
Review Comment:
nit: this name seems a bit off to me. Also javadocs.
##########
hadoop-common-project/hadoop-common/src/main/resources/core-default.xml:
##########
@@ -1364,6 +1364,24 @@
<description>File space usage statistics refresh interval in
msec.</description>
</property>
+<property>
+ <name>fs.file.checksum.verify</name>
+ <value>true</value>
+ <description>
+ Should data read through the local filesystem (file://) URLs be verified
aginst
+ the checksums stored in the associated checksum files?
+ Setting this to false skips loading the checksum files, reading data in
checksum-aligned
+ blocks and verifying checksums. This may improve performance
+ when reading data, though it pushes the responsibility of detecting errors
+ into the file formats themselves, or the underlying storage system.
+ Even when verification is enabled, files without associated checksum files
+ .$FILENAME.crc are never be verified.
Review Comment:
nit: typo extra "be"
##########
hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/contract/AbstractContractVectoredReadTest.java:
##########
@@ -619,4 +625,61 @@ protected <T extends Throwable> void
verifyExceptionalVectoredRead(
});
}
}
+
+ @Test
+ public void testBufferSlicing() throws Throwable {
+ describe("Test buffer slicing behavior in vectored IO");
+
+ final int numBuffers = 8;
+ final int bufferSize = S_4K;
+ long offset = 0;
+ final List<FileRange> fileRanges = new ArrayList<>();
+ for (int i = 0; i < numBuffers; i++) {
+ fileRanges.add(FileRange.createFileRange(offset, bufferSize));
+ // increment and add a non-binary-aligned gap, so as to force
+ // offsets to be misaligned with possible page sizes.
+ offset += bufferSize + 4000;
+ }
+ TrackingByteBufferPool trackerPool =
TrackingByteBufferPool.wrap(getPool());
+ int unknownBuffers = 0;
+ boolean slicing;
+ try (FSDataInputStream in = openVectorFile()) {
+ slicing = in.hasCapability(VECTOREDIO_BUFFERS_SLICED);
+ LOG.info("Slicing is {} for vectored IO with stream {}", slicing, in);
+ in.readVectored(fileRanges, s -> trackerPool.getBuffer(isDirect, s),
trackerPool::putBuffer);
+
+ // check that all buffers are from the the pool, unless they are sliced.
+ for (FileRange res : fileRanges) {
+ CompletableFuture<ByteBuffer> data = res.getData();
+ ByteBuffer buffer = awaitFuture(data);
+ Assertions.assertThat(buffer)
+ .describedAs("Buffer must not be null")
+ .isNotNull();
+ Assertions.assertThat(slicing || trackerPool.containsBuffer(buffer))
+ .describedAs("Buffer must be from the pool")
+ .isTrue();
+ try {
+ trackerPool.putBuffer(buffer);
+ } catch
(TrackingByteBufferPool.ReleasingUnallocatedByteBufferException e) {
+ // this can happen if the buffer was sliced, as it is not in the
pool.
+ if (!slicing) {
+ throw e;
+ }
+ LOG.info("Sliced buffer detected: {}", buffer);
+ unknownBuffers++;
+ }
+ }
+ }
+ try {
+ trackerPool.close();
+ } catch (TrackingByteBufferPool.LeakedByteBufferException e) {
+ if (!slicing) {
+ throw e;
+ }
+ LOG.info("Slicing is enabled; we saw leaked buffers: {} after {}"
Review Comment:
shouldn't this LOG be outside of the catch block?
##########
hadoop-common-project/hadoop-common/src/site/markdown/filesystem/fsdatainputstream.md:
##########
@@ -665,8 +665,48 @@ support through an explicit `hasCapability()` probe:
Stream.hasCapability("in:readvectored")
```
-Given the HADOOP-18296 problem with `ChecksumFileSystem` and direct buffers,
across all releases,
-it is best to avoid using this API in production with direct buffers.
+#### Buffer Slicing
+
+[HADOOP-18296](https://issues.apache.org/jira/browse/HADOOP-18296),
+_Memory fragmentation in ChecksumFileSystem Vectored IO implementation_
+highlights that `ChecksumFileSystem` (which the default implementation of
`file://`
+subclasses), may return buffers which are sliced subsets of buffers allocated
+through the `allocate()` function passed in.
+
+This will happen during reads with and without range coalescing.
+
+Checksum verification may be disabled by setting the option
+`fs.file.checksum.verify` to true (Hadoop 3.4.2 and later).
Review Comment:
typo: option to false.
> Memory fragmentation in ChecksumFileSystem Vectored IO implementation.
> ----------------------------------------------------------------------
>
> Key: HADOOP-18296
> URL: https://issues.apache.org/jira/browse/HADOOP-18296
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: common
> Affects Versions: 3.4.0
> Reporter: Mukund Thakur
> Assignee: Steve Loughran
> Priority: Minor
> Labels: fs, pull-request-available
>
> As we have implemented merging of ranges in the ChecksumFSInputChecker
> implementation of vectored IO api, it can lead to memory fragmentation. Let
> me explain by example.
>
> Suppose client requests for 3 ranges.
> 0-500, 700-1000 and 1200-1500.
> Now because of merging, all the above ranges will get merged into one and we
> will allocate a big byte buffer of 0-1500 size but return sliced byte buffers
> for the desired ranges.
> Now once the client is done reading all the ranges, it will only be able to
> free the memory for requested ranges and memory of the gaps will never be
> released for eg here (500-700 and 1000-1200).
>
> Note this only happens for direct byte buffers.
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