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HADOOP-18407. Improve readVectored() api spec (#4760) 

part of HADOOP-18103.

Contributed By: Mukund Thakur
This commit is contained in:
Mukund Thakur 2022-08-22 23:19:29 +05:30 committed by GitHub
parent a9e5fb3313
commit 231e095802
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10
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/PositionedReadable.java
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@ -114,6 +114,16 @@ public interface PositionedReadable {
* As a result of the call, each range will have FileRange.setData(CompletableFuture)
* called with a future that when complete will have a ByteBuffer with the
* data from the file's range.
* <p>
* The position returned by getPos() after readVectored() is undefined.
* </p>
* <p>
* If a file is changed while the readVectored() operation is in progress, the output is
* undefined. Some ranges may have old data, some may have new and some may have both.
* </p>
* <p>
* While a readVectored() operation is in progress, normal read api calls may block.
* </p>
* @param ranges the byte ranges to read
* @param allocate the function to allocate ByteBuffer
* @throws IOException any IOE.

7
hadoop-common-project/hadoop-common/src/site/markdown/filesystem/fsdatainputstream.md
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@ -454,6 +454,13 @@ Also, clients are encouraged to use `WeakReferencedElasticByteBufferPool` for
allocating buffers such that even direct buffers are garbage collected when
they are no longer referenced.
The position returned by `getPos()` after `readVectored()` is undefined.
If a file is changed while the `readVectored()` operation is in progress, the output is
undefined. Some ranges may have old data, some may have new, and some may have both.
While a `readVectored()` operation is in progress, normal read api calls may block.
Note: Don't use direct buffers for reading from ChecksumFileSystem as that may
lead to memory fragmentation explained in HADOOP-18296.