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@@ -449,6 +449,80 @@ creations/deletions), or "all".</description>
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</description>
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</property>
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+<property>
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+ <name>dfs.datanode.readahead.bytes</name>
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+ <value>4193404</value>
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+ <description>
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+ While reading block files, if the Hadoop native libraries are available,
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+ the datanode can use the posix_fadvise system call to explicitly
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+ page data into the operating system buffer cache ahead of the current
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+ reader's position. This can improve performance especially when
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+ disks are highly contended.
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+
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+ This configuration specifies the number of bytes ahead of the current
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+ read position which the datanode will attempt to read ahead. This
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+ feature may be disabled by configuring this property to 0.
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+
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+ If the native libraries are not available, this configuration has no
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+ effect.
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+ </description>
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+</property>
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+
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+<property>
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+ <name>dfs.datanode.drop.cache.behind.reads</name>
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+ <value>false</value>
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+ <description>
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+ In some workloads, the data read from HDFS is known to be significantly
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+ large enough that it is unlikely to be useful to cache it in the
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+ operating system buffer cache. In this case, the DataNode may be
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+ configured to automatically purge all data from the buffer cache
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+ after it is delivered to the client. This behavior is automatically
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+ disabled for workloads which read only short sections of a block
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+ (e.g HBase random-IO workloads).
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+
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+ This may improve performance for some workloads by freeing buffer
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+ cache spage usage for more cacheable data.
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+
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+ If the Hadoop native libraries are not available, this configuration
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+ has no effect.
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+ </description>
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+</property>
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+
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+<property>
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+ <name>dfs.datanode.drop.cache.behind.writes</name>
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+ <value>false</value>
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+ <description>
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+ In some workloads, the data written to HDFS is known to be significantly
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+ large enough that it is unlikely to be useful to cache it in the
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+ operating system buffer cache. In this case, the DataNode may be
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+ configured to automatically purge all data from the buffer cache
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+ after it is written to disk.
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+
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+ This may improve performance for some workloads by freeing buffer
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+ cache spage usage for more cacheable data.
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+
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+ If the Hadoop native libraries are not available, this configuration
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+ has no effect.
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+ </description>
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+</property>
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+
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+<property>
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+ <name>dfs.datanode.sync.behind.writes</name>
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+ <value>false</value>
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+ <description>
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+ If this configuration is enabled, the datanode will instruct the
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+ operating system to enqueue all written data to the disk immediately
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+ after it is written. This differs from the usual OS policy which
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+ may wait for up to 30 seconds before triggering writeback.
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+
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+ This may improve performance for some workloads by smoothing the
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+ IO profile for data written to disk.
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+
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+ If the Hadoop native libraries are not available, this configuration
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+ has no effect.
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+ </description>
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+</property>
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+
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<property>
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<name>dfs.client.use.datanode.hostname</name>
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<value>false</value>
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Eli Collins