Critical Description
Apache Hadoop 1.2.0 ships with the durable sync enabled by default and the support append option marked as obsolete. Because of this, the check inside of TabletServer, meant to ensure that the HDFS WAL can function properly, incorrectly fails as it doesn't know that dfs.durable.sync is on by default.
This can be worked around by specifying the old durable sync property in hdfs-site.xml:
<property> <name>dfs.durable.sync</name> <value>true</value> </property>
I'm not sure how to best way to address the differences between the newer and older versions of Hadoop and their differing append support.
Thanks to Carlos Mundi for pointing this out on user@a.a.o
Using this table to track the presence of these variables and their default from hdfs/o/a/h/h/DFSConfigKeys and from the codebase when there is no config parameter for it.
| Version | DFSConfigKeys.DFS_SUPPORT_APPEND_KEY | DFSConfigKeys.DFS_SUPPORT_APPEND_DEFAULT | "dfs.durable.sync" | Specific Configuration Required |
|---|---|---|---|---|
| 0.20.205.0 | defined | false | not present | yes |
| 0.23.x | defined | true | not present | no |
| 1.0.x | defined | false | not present | yes |
| 1.1.X | not present | absent | implicit "true" | no |
| 1.2.X | not present | absent | implicit "true" | no |
| 2.0.x | defined | true | not present | no |
| 2.1.x | defined | true | not present | no |
| 2.2.0 | defined | true | not present | no |