Uma Maheswara Rao G created HDFS-15533:
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Summary: Provide DFS API compatible call, but use
ViewFileSystemOverloadScheme inside
Key: HDFS-15533
URL: https://issues.apache.org/jira/browse/HDFS-15533
Project: Hadoop HDFS
Issue Type: Sub-task
Components: dfs, viewfs
Affects Versions: 3.4.0
Reporter: Uma Maheswara Rao G
Assignee: Uma Maheswara Rao G
I have been working on a thought from last week is that, we wanted to provide
DFS compatible APIs with mount functionality. So, that existing DFS
applications can work with out class cast issues.
When we tested with other components like Hive and HBase, I noticed some
classcast issues.
{code:java}
HBase example:
java.lang.ClassCastException:
org.apache.hadoop.fs.viewfs.ViewFileSystemOverloadScheme cannot be cast to
org.apache.hadoop.hdfs.DistributedFileSystemjava.lang.ClassCastException:
org.apache.hadoop.fs.viewfs.ViewFileSystemOverloadScheme cannot be cast to
org.apache.hadoop.hdfs.DistributedFileSystem at
org.apache.hadoop.hbase.util.FSUtils.getDFSHedgedReadMetrics(FSUtils.java:1748)
at
org.apache.hadoop.hbase.regionserver.MetricsRegionServerWrapperImpl.<init>(MetricsRegionServerWrapperImpl.java:146)
at
org.apache.hadoop.hbase.regionserver.HRegionServer.handleReportForDutyResponse(HRegionServer.java:1594)
at
org.apache.hadoop.hbase.regionserver.HRegionServer.run(HRegionServer.java:1001)
at java.lang.Thread.run(Thread.java:748){code}
{code:java}
Hive:
|io.AcidUtils|: Failed to get files with ID; using regular API: Only supported
for DFS; got class
org.apache.hadoop.fs.viewfs.ViewFileSystemOverloadScheme{code}
SO, here the implementation details are like follows:
We extended DistributedFileSystem and created a class called "
ViewDistributedFileSystem"
This vfs=ViewFirstibutedFileSystem, try to initialize
ViewFileSystemOverloadScheme. If success call will delegate to vfs. If fails
to initialize due to no mount points, or other errors, it will just fallback to
regular DFS init. If users does not configure any mount, system will behave
exactly like today's DFS. If there are mount points, vfs functionality will
come under DFS.
I will a patch and will post it in some time.
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