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Posted to hdfs-commits@hadoop.apache.org by cn...@apache.org on 2013/10/30 20:01:13 UTC
svn commit: r1537243 - in
/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs: CHANGES.txt
src/main/resources/hdfs-default.xml
src/site/apt/CentralizedCacheManagement.apt.vm
src/site/resources/images/caching.png
Author: cnauroth
Date: Wed Oct 30 19:01:13 2013
New Revision: 1537243
URL: http://svn.apache.org/r1537243
Log:
HDFS-5386. Add feature documentation for datanode caching. Contributed by Colin Patrick McCabe.
Added:
hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/CentralizedCacheManagement.apt.vm
hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/resources/images/caching.png (with props)
Modified:
hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
Modified: hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
URL: http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt?rev=1537243&r1=1537242&r2=1537243&view=diff
==============================================================================
--- hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt (original)
+++ hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt Wed Oct 30 19:01:13 2013
@@ -188,6 +188,9 @@ Trunk (Unreleased)
HDFS-5378. In CacheReport, don't send genstamp and length on the wire
(Contributed by Colin Patrick McCabe)
+ HDFS-5386. Add feature documentation for datanode caching.
+ (Colin Patrick McCabe via cnauroth)
+
OPTIMIZATIONS
HDFS-5349. DNA_CACHE and DNA_UNCACHE should be by blockId only. (cmccabe)
Modified: hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
URL: http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml?rev=1537243&r1=1537242&r2=1537243&view=diff
==============================================================================
--- hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml (original)
+++ hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml Wed Oct 30 19:01:13 2013
@@ -1487,6 +1487,24 @@
</property>
<property>
+ <name>dfs.namenode.list.cache.descriptors.num.responses</name>
+ <value>100</value>
+ <description>
+ This value controls the number of cache descriptors that the NameNode will
+ send over the wire in response to a listDirectives RPC.
+ </description>
+</property>
+
+<property>
+ <name>dfs.namenode.list.cache.pools.num.responses</name>
+ <value>100</value>
+ <description>
+ This value controls the number of cache pools that the NameNode will
+ send over the wire in response to a listPools RPC.
+ </description>
+</property>
+
+<property>
<name>dfs.namenode.path.based.cache.refresh.interval.ms</name>
<value>300000</value>
<description>
Added: hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/CentralizedCacheManagement.apt.vm
URL: http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/CentralizedCacheManagement.apt.vm?rev=1537243&view=auto
==============================================================================
--- hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/CentralizedCacheManagement.apt.vm (added)
+++ hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/apt/CentralizedCacheManagement.apt.vm Wed Oct 30 19:01:13 2013
@@ -0,0 +1,300 @@
+~~ Licensed under the Apache License, Version 2.0 (the "License");
+~~ you may not use this file except in compliance with the License.
+~~ You may obtain a copy of the License at
+~~
+~~ http://www.apache.org/licenses/LICENSE-2.0
+~~
+~~ Unless required by applicable law or agreed to in writing, software
+~~ distributed under the License is distributed on an "AS IS" BASIS,
+~~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+~~ See the License for the specific language governing permissions and
+~~ limitations under the License. See accompanying LICENSE file.
+
+ ---
+ Hadoop Distributed File System-${project.version} - Centralized Cache Management in HDFS
+ ---
+ ---
+ ${maven.build.timestamp}
+
+Centralized Cache Management in HDFS
+
+ \[ {{{./index.html}Go Back}} \]
+
+%{toc|section=1|fromDepth=2|toDepth=4}
+
+* {Background}
+
+ Normally, HDFS relies on the operating system to cache data it reads from disk.
+ However, HDFS can also be configured to use centralized cache management. Under
+ centralized cache management, the HDFS NameNode itself decides which blocks
+ should be cached, and where they should be cached.
+
+ Centralized cache management has several advantages. First of all, it
+ prevents frequently used block files from being evicted from memory. This is
+ particularly important when the size of the working set exceeds the size of
+ main memory, which is true for many big data applications. Secondly, when
+ HDFS decides what should be cached, it can let clients know about this
+ information through the getFileBlockLocations API. Finally, when the DataNode
+ knows a block is locked into memory, it can provide access to that block via
+ mmap.
+
+* {Use Cases}
+
+ Centralized cache management is most useful for files which are accessed very
+ often. For example, a "fact table" in Hive which is often used in joins is a
+ good candidate for caching. On the other hand, when running a classic
+ "word count" MapReduce job which counts the number of words in each
+ document, there may not be any good candidates for caching, since all the
+ files may be accessed exactly once.
+
+* {Architecture}
+
+[images/caching.png] Caching Architecture
+
+ With centralized cache management, the NameNode coordinates all caching
+ across the cluster. It receives cache information from each DataNode via the
+ cache report, a periodic message that describes all the blocks IDs cached on
+ a given DataNode. The NameNode will reply to DataNode heartbeat messages
+ with commands telling it which blocks to cache and which to uncache.
+
+ The NameNode stores a set of path cache directives, which tell it which files
+ to cache. The NameNode also stores a set of cache pools, which are groups of
+ cache directives. These directives and pools are persisted to the edit log
+ and fsimage, and will be loaded if the cluster is restarted.
+
+ Periodically, the NameNode rescans the namespace, to see which blocks need to
+ be cached based on the current set of path cache directives. Rescans are also
+ triggered by relevant user actions, such as adding or removing a cache
+ directive or removing a cache pool.
+
+ Cache directives also may specific a numeric cache replication, which is the
+ number of replicas to cache. This number may be equal to or smaller than the
+ file's block replication. If multiple cache directives cover the same file
+ with different cache replication settings, then the highest cache replication
+ setting is applied.
+
+ We do not currently cache blocks which are under construction, corrupt, or
+ otherwise incomplete. If a cache directive covers a symlink, the symlink
+ target is not cached.
+
+ Caching is currently done on a per-file basis, although we would like to add
+ block-level granularity in the future.
+
+* {Interface}
+
+ The NameNode stores a list of "cache directives." These directives contain a
+ path as well as the number of times blocks in that path should be replicated.
+
+ Paths can be either directories or files. If the path specifies a file, that
+ file is cached. If the path specifies a directory, all the files in the
+ directory will be cached. However, this process is not recursive-- only the
+ direct children of the directory will be cached.
+
+** {hdfs cacheadmin Shell}
+
+ Path cache directives can be created by the <<<hdfs cacheadmin
+ -addDirective>>> command and removed via the <<<hdfs cacheadmin
+ -removeDirective>>> command. To list the current path cache directives, use
+ <<<hdfs cacheadmin -listDirectives>>>. Each path cache directive has a
+ unique 64-bit ID number which will not be reused if it is deleted. To remove
+ all path cache directives with a specified path, use <<<hdfs cacheadmin
+ -removeDirectives>>>.
+
+ Directives are grouped into "cache pools." Each cache pool gets a share of
+ the cluster's resources. Additionally, cache pools are used for
+ authentication. Cache pools have a mode, user, and group, similar to regular
+ files. The same authentication rules are applied as for normal files. So, for
+ example, if the mode is 0777, any user can add or remove directives from the
+ cache pool. If the mode is 0644, only the owner can write to the cache pool,
+ but anyone can read from it. And so forth.
+
+ Cache pools are identified by name. They can be created by the <<<hdfs
+ cacheAdmin -addPool>>> command, modified by the <<<hdfs cacheadmin
+ -modifyPool>>> command, and removed via the <<<hdfs cacheadmin
+ -removePool>>> command. To list the current cache pools, use <<<hdfs
+ cacheAdmin -listPools>>>
+
+*** {addDirective}
+
+ Usage: <<<hdfs cacheadmin -addDirective -path <path> -replication <replication> -pool <pool-name> >>>
+
+ Add a new PathBasedCache directive.
+
+*--+--+
+\<path\> | A path to cache. The path can be a directory or a file.
+*--+--+
+\<replication\> | The cache replication factor to use. Defaults to 1.
+*--+--+
+\<pool-name\> | The pool to which the directive will be added. You must have write permission on the cache pool in order to add new directives.
+*--+--+
+
+*** {removeDirective}
+
+ Usage: <<<hdfs cacheadmin -removeDirective <id> >>>
+
+ Remove a cache directive.
+
+*--+--+
+\<id\> | The id of the cache directive to remove. You must have write permission on the pool of the directive in order to remove it. To see a list of PathBasedCache directive IDs, use the -listDirectives command.
+*--+--+
+
+*** {removeDirectives}
+
+ Usage: <<<hdfs cacheadmin -removeDirectives <path> >>>
+
+ Remove every cache directive with the specified path.
+
+*--+--+
+\<path\> | The path of the cache directives to remove. You must have write permission on the pool of the directive in order to remove it. To see a list of cache directives, use the -listDirectives command.
+*--+--+
+
+*** {listDirectives}
+
+ Usage: <<<hdfs cacheadmin -listDirectives [-path <path>] [-pool <pool>] >>>
+
+ List PathBasedCache directives.
+
+*--+--+
+\<path\> | List only PathBasedCache directives with this path. Note that if there is a PathBasedCache directive for <path> in a cache pool that we don't have read access for, it will not be listed.
+*--+--+
+\<pool\> | List only path cache directives in that pool.
+*--+--+
+
+*** {addPool}
+
+ Usage: <<<hdfs cacheadmin -addPool <name> [-owner <owner>] [-group <group>] [-mode <mode>] [-weight <weight>] >>>
+
+ Add a new cache pool.
+
+*--+--+
+\<name\> | Name of the new pool.
+*--+--+
+\<owner\> | Username of the owner of the pool. Defaults to the current user.
+*--+--+
+\<group\> | Group of the pool. Defaults to the primary group name of the current user.
+*--+--+
+\<mode\> | UNIX-style permissions for the pool. Permissions are specified in octal, e.g. 0755. By default, this is set to 0755.
+*--+--+
+\<weight\> | Weight of the pool. This is a relative measure of the importance of the pool used during cache resource management. By default, it is set to 100.
+*--+--+
+
+*** {modifyPool}
+
+ Usage: <<<hdfs cacheadmin -modifyPool <name> [-owner <owner>] [-group <group>] [-mode <mode>] [-weight <weight>] >>>
+
+ Modifies the metadata of an existing cache pool.
+
+*--+--+
+\<name\> | Name of the pool to modify.
+*--+--+
+\<owner\> | Username of the owner of the pool.
+*--+--+
+\<group\> | Groupname of the group of the pool.
+*--+--+
+\<mode\> | Unix-style permissions of the pool in octal.
+*--+--+
+\<weight\> | Weight of the pool.
+*--+--+
+
+*** {removePool}
+
+ Usage: <<<hdfs cacheadmin -removePool <name> >>>
+
+ Remove a cache pool. This also uncaches paths associated with the pool.
+
+*--+--+
+\<name\> | Name of the cache pool to remove.
+*--+--+
+
+*** {listPools}
+
+ Usage: <<<hdfs cacheadmin -listPools [name] >>>
+
+ Display information about one or more cache pools, e.g. name, owner, group,
+ permissions, etc.
+
+*--+--+
+\<name\> | If specified, list only the named cache pool.
+*--+--+
+
+*** {help}
+
+ Usage: <<<hdfs cacheadmin -help <command-name> >>>
+
+ Get detailed help about a command.
+
+*--+--+
+\<command-name\> | The command for which to get detailed help. If no command is specified, print detailed help for all commands.
+*--+--+
+
+* {Configuration}
+
+** {Native Libraries}
+
+ In order to lock block files into memory, the DataNode relies on native JNI
+ code found in <<<libhadoop.so>>>. Be sure to
+ {{{../hadoop-common/NativeLibraries.html}enable JNI}} if you are using HDFS
+ centralized cache management.
+
+** {Configuration Properties}
+
+*** Required
+
+ Be sure to configure the following:
+
+ * dfs.namenode.caching.enabled
+
+ This must be set to true to enable caching. If this is false, the NameNode
+ will ignore cache reports, and will not ask DataNodes to cache
+ blocks.
+
+ * dfs.datanode.max.locked.memory
+
+ The DataNode will treat this as the maximum amount of memory it can use for
+ its cache. When setting this value, please remember that you will need space
+ in memory for other things, such as the Java virtual machine (JVM) itself
+ and the operating system's page cache.
+
+*** Optional
+
+ The following properties are not required, but may be specified for tuning:
+
+ * dfs.namenode.path.based.cache.refresh.interval.ms
+
+ The NameNode will use this as the amount of milliseconds between subsequent
+ path cache rescans. This calculates the blocks to cache and each DataNode
+ containing a replica of the block that should cache it.
+
+ By default, this parameter is set to 300000, which is five minutes.
+
+ * dfs.datanode.fsdatasetcache.max.threads.per.volume
+
+ The DataNode will use this as the maximum number of threads per volume to
+ use for caching new data.
+
+ By default, this parameter is set to 4.
+
+ * dfs.cachereport.intervalMsec
+
+ The DataNode will use this as the amount of milliseconds between sending a
+ full report of its cache state to the NameNode.
+
+ By default, this parameter is set to 10000, which is 10 seconds.
+
+** {OS Limits}
+
+ If you get the error "Cannot start datanode because the configured max
+ locked memory size... is more than the datanode's available RLIMIT_MEMLOCK
+ ulimit," that means that the operating system is imposing a lower limit
+ on the amount of memory that you can lock than what you have configured. To
+ fix this, you must adjust the ulimit -l value that the DataNode runs with.
+ Usually, this value is configured in <<</etc/security/limits.conf>>>.
+ However, it will vary depending on what operating system and distribution
+ you are using.
+
+ You will know that you have correctly configured this value when you can run
+ <<<ulimit -l>>> from the shell and get back either a higher value than what
+ you have configured with <<<dfs.datanode.max.locked.memory>>>, or the string
+ "unlimited," indicating that there is no limit. Note that it's typical for
+ <<<ulimit -l>>> to output the memory lock limit in KB, but
+ dfs.datanode.max.locked.memory must be specified in bytes.
Added: hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/resources/images/caching.png
URL: http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/site/resources/images/caching.png?rev=1537243&view=auto
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