There has been some discussion on the JIRA lately about what to do about a 0.92/0.94 compatibility issue. I wanted to bring this up to a larger audience in order to solicit additional opinions.
HBASE-5206 (https://issues.apache.org/jira/browse/HBASE-5206), which is in 0.94.0 and 0.94.1, breaks compatibility with 0.92.0 and 0.92.1. The issue is described in the release notes for HBASE-5155 (of which HBASE-5206 is a forward port). Excerpted here: This issue is an incompatible change. If an HBase client with the changes for HBASE-5155 and a server (master) without the changes for HBASE-5155 is used, then the is_enabled (from HBase Shell) or isTableEnabled() (from HBaseAdmin) will return false though the table is already enabled as per the master. If the HBase client does have the changes for HBASE-5155 and the server does not have the changes for HBASE-5155, then if we try to Enable a table then the client will hang. The reason is because, Prior to HBASE-5155 once the table is enabled the znode in the zookeeper created for the table is deleted. After HBASE-5155 once the table is enabled the znode in the zookeeper created for the table is not deleted, whereas the same node is updated with the status ENABLED. The client also expects the status of the znode in the zookeeper to be in the ENABLED state if the table has been enabled successfully. The above changes makes the client behaviour incompatible if the client does not have this fix whereas the server has this fix. If both the client and the server does not have this fix, then the behaviour is as expected. So we have a situation where 0.92.0 and 0.92.1 clients are not compatible with 0.94.0 and 0.94.1 servers and visa-versa. The issue is, what should we do about the 0.94.2 server? As far as I can tell, we cannot make both {0.92.0,0.92.1} and {0.94.0,0.94.1} clients happy. I propose we make the 0.94.2 server compatible with the {0.92.0, 0.92.1} client set. My thinking is that we should optimize for the most common use case. Given that both CDH4 and HDP 1.0 ship 0.92.1, and that 0.94 is relatively new, it seems more likely that users will upgrade servers from 0.92.1 to 0.94.2+ than from an earlier 0.94 version. I think we can do this while actually fixing the issue that HBASE-5206 purports to fix by moving the ENABLED state to a different znode. I'll even volunteer to do that :). I don't think there is an obvious or easy answer here, so wanted to get other's opinions. As for the client, HBASE-6268 ( https://issues.apache.org/jira/browse/HBASE-6268) was introduced in 0.92.2 to handle both cases of servers ({0.92.0,0.92.1} and {0.94.0,0.94.1}) by accepting both possibilities for the table znode. I think that approach works whether we leave the server as is or go with what I've proposed -- but we should test. Greg
