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Posted to hdfs-commits@hadoop.apache.org by to...@apache.org on 2011/06/03 22:44:50 UTC
svn commit: r1131224 - in /hadoop/hdfs/branches/branch-0.22: CHANGES.txt
src/docs/src/documentation/content/xdocs/hdfs_design.xml
Author: todd
Date: Fri Jun 3 20:44:49 2011
New Revision: 1131224
URL: http://svn.apache.org/viewvc?rev=1131224&view=rev
Log:
HDFS-1454. Update the documentation to reflect that clients don't write blocks to local disk before copying to HDFS. Contributed by Harsh J Chouraria.
Modified:
hadoop/hdfs/branches/branch-0.22/CHANGES.txt
hadoop/hdfs/branches/branch-0.22/src/docs/src/documentation/content/xdocs/hdfs_design.xml
Modified: hadoop/hdfs/branches/branch-0.22/CHANGES.txt
URL: http://svn.apache.org/viewvc/hadoop/hdfs/branches/branch-0.22/CHANGES.txt?rev=1131224&r1=1131223&r2=1131224&view=diff
==============================================================================
--- hadoop/hdfs/branches/branch-0.22/CHANGES.txt (original)
+++ hadoop/hdfs/branches/branch-0.22/CHANGES.txt Fri Jun 3 20:44:49 2011
@@ -249,6 +249,9 @@ Release 0.22.0 - Unreleased
HDFS-1957. Add documentation for HFTP. (Ari Rabkin via todd)
+ HDFS-1454. Update the documentation to reflect that clients don't write
+ blocks to local disk before copying to HDFS. (Harsh J Chouraria via todd)
+
OPTIMIZATIONS
HDFS-1140. Speedup INode.getPathComponents. (Dmytro Molkov via shv)
Modified: hadoop/hdfs/branches/branch-0.22/src/docs/src/documentation/content/xdocs/hdfs_design.xml
URL: http://svn.apache.org/viewvc/hadoop/hdfs/branches/branch-0.22/src/docs/src/documentation/content/xdocs/hdfs_design.xml?rev=1131224&r1=1131223&r2=1131224&view=diff
==============================================================================
--- hadoop/hdfs/branches/branch-0.22/src/docs/src/documentation/content/xdocs/hdfs_design.xml (original)
+++ hadoop/hdfs/branches/branch-0.22/src/docs/src/documentation/content/xdocs/hdfs_design.xml Fri Jun 3 20:44:49 2011
@@ -387,41 +387,11 @@
</p>
</section>
-
- <section>
- <!-- XXX staging never described / referenced in its section -->
- <title> Staging </title>
- <p>
- A client request to create a file does not reach the NameNode immediately. In fact, initially the HDFS
- client caches the file data into a temporary local file. Application writes are transparently redirected to
- this temporary local file. When the local file accumulates data worth over one HDFS block size, the
- client contacts the NameNode. The NameNode inserts the file name into the file system hierarchy
- and allocates a data block for it. The NameNode responds to the client request with the identity
- of the DataNode and the destination data block. Then the client flushes the block of data from the
- local temporary file to the specified DataNode. When a file is closed, the remaining un-flushed data
- in the temporary local file is transferred to the DataNode. The client then tells the NameNode that
- the file is closed. At this point, the NameNode commits the file creation operation into a persistent
- store. If the NameNode dies before the file is closed, the file is lost.
- </p>
- <p>
- The above approach has been adopted after careful consideration of target applications that run on
- HDFS. These applications need streaming writes to files. If a client writes to a remote file directly
- without any client side buffering, the network speed and the congestion in the network impacts
- throughput considerably. This approach is not without precedent. Earlier distributed file systems,
- e.g. <acronym title="Andrew File System">AFS</acronym>, have used client side caching to
- improve performance. A POSIX requirement has been relaxed to achieve higher performance of
- data uploads.
- </p>
- </section>
-
<section>
<title> Replication Pipelining </title>
<p>
- When a client is writing data to an HDFS file, its data is first written to a local file as explained
- in the previous section. Suppose the HDFS file has a replication factor of three. When the local
- file accumulates a full block of user data, the client retrieves a list of DataNodes from the NameNode.
- This list contains the DataNodes that will host a replica of that block. The client then flushes the
- data block to the first DataNode. The first DataNode starts receiving the data in small portions (4 KB),
+ When a client is writing data to an HDFS file with a replication factor of 3, the NameNode retrieves a list of DataNodes using a replication target choosing algorithm.
+ This list contains the DataNodes that will host a replica of that block. The client then writes to the first DataNode. The first DataNode starts receiving the data in small portions (4 KB),
writes each portion to its local repository and transfers that portion to the second DataNode in the list.
The second DataNode, in turn starts receiving each portion of the data block, writes that portion to its
repository and then flushes that portion to the third DataNode. Finally, the third DataNode writes the