https://community.cloudera.com/t5/Support-Questions/what-is-meaning-of-datanode-numBlocksFailedToUncache-metric/m-p/313837#M225754 <P>Hello</P><P>&nbsp;</P><P>This is related to the Cache Management of HDFS</P><P>&nbsp;</P><P>As described in the documentation:&nbsp;<A href="https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/CentralizedCacheManagement.html#:~:text=Centralized%20cache%20management%20in%20HDFS%20is%20an%20explicit%20caching%20mechanism,blocks%20in%20off%2Dheap%20caches" target="_blank">https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/CentralizedCacheManagement.html</A></P><P>&nbsp;</P><P><SPAN>In this architecture, the NameNode is responsible for coordinating all the DataNode off-heap caches in the cluster. The NameNode periodically receives a&nbsp;</SPAN><I>cache report</I><SPAN>&nbsp;from each DataNode which describes all the blocks cached on a given DN. The NameNode manages DataNode caches by piggybacking <STRONG><FONT color="#000000">cache</FONT></STRONG> and <STRONG><FONT color="#000000">uncache</FONT></STRONG> commands on the DataNode heartbeat.</SPAN></P><P>&nbsp;</P><P>If the metric is going up, one possibility could be your namenode is too busy to handle the request</P><P>&nbsp;</P><P>&nbsp;</P><P>&nbsp;</P> Tue, 30 Mar 2021 09:13:28 GMT Daming Xue 2021-03-30T09:13:28Z https://community.cloudera.com/t5/Support-Questions/what-is-meaning-of-datanode-numBlocksFailedToUncache-metric/m-p/313801#M225729 <P>Hello,</P><P>&nbsp;</P><P>I am seeing this value for numBlocksFailedToUncache property is going up. Should I be concerned? From apache documentation I can see it means <A href="https://blog.woopi.org/wordpress/files/hadoop-2.6.0-javadoc/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetCache.html" target="_blank" rel="noopener">https://blog.woopi.org/wordpress/files/hadoop-2.6.0-javadoc/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetCache.html</A></P><P>"<SPAN>Number of uncache commands that could not be completed successfully" Not sure how to interpret&nbsp;this..</SPAN></P><P>&nbsp;</P><P><SPAN>Thanks</SPAN></P><P><SPAN>M</SPAN></P> Mon, 29 Mar 2021 14:39:54 GMT https://community.cloudera.com/t5/Support-Questions/what-is-meaning-of-datanode-numBlocksFailedToUncache-metric/m-p/313801#M225729 SDL 2021-03-29T14:39:54Z https://community.cloudera.com/t5/Support-Questions/what-is-meaning-of-datanode-numBlocksFailedToUncache-metric/m-p/313837#M225754 <P>Hello</P><P>&nbsp;</P><P>This is related to the Cache Management of HDFS</P><P>&nbsp;</P><P>As described in the documentation:&nbsp;<A href="https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/CentralizedCacheManagement.html#:~:text=Centralized%20cache%20management%20in%20HDFS%20is%20an%20explicit%20caching%20mechanism,blocks%20in%20off%2Dheap%20caches" target="_blank">https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/CentralizedCacheManagement.html</A></P><P>&nbsp;</P><P><SPAN>In this architecture, the NameNode is responsible for coordinating all the DataNode off-heap caches in the cluster. The NameNode periodically receives a&nbsp;</SPAN><I>cache report</I><SPAN>&nbsp;from each DataNode which describes all the blocks cached on a given DN. The NameNode manages DataNode caches by piggybacking <STRONG><FONT color="#000000">cache</FONT></STRONG> and <STRONG><FONT color="#000000">uncache</FONT></STRONG> commands on the DataNode heartbeat.</SPAN></P><P>&nbsp;</P><P>If the metric is going up, one possibility could be your namenode is too busy to handle the request</P><P>&nbsp;</P><P>&nbsp;</P><P>&nbsp;</P> Tue, 30 Mar 2021 09:13:28 GMT https://community.cloudera.com/t5/Support-Questions/what-is-meaning-of-datanode-numBlocksFailedToUncache-metric/m-p/313837#M225754 Daming Xue 2021-03-30T09:13:28Z