z-york commented on pull request #2113: URL: https://github.com/apache/hbase/pull/2113#issuecomment-663260010
So the use case here is starting a new cluster in the cloud where HDFS (WAL) data on the previous cluster will not be available. One of the benefits of storing the data off the cluster (in our case, S3), is to not have to replicate data (and just create a new cluster pointed to the same root directory). IMO, in this case we shouldn't need the WAL directories to exist just to tell us to reassign and this is a valid use case. I get that there is pushback for enabling this in the catalog cleaner, and I think that's fine. For this case, it's a one time issue, not something that periodically needs fixing. (there might be other unknown server cases that would require that, but that isn't blocking us at the moment). So, instead maybe a 1-time run to cleanup old servers/schedule SCP for them (this is what the code that was removed in HBASE-20708 actually did) makes the most sense? I understand that it was removed to simplify the assignment, but it has a very different behavior. In fact it looks like we don't even try to read hbase:meta if it is found (without SCP/WAL) and simply just delete the directory[1]. What problem is being solved by deleting instead of trying to assign it if data is there? [1] https://github.com/apache/hbase/blob/bad2d4e409ba57014e0f5931b72e54cc397e268a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/InitMetaProcedure.java#L75-L81 > For your scenario, it is OK as you can confirm that there is no data loss as you manually flushed all the data. But what if another user just configs the wrong WAL directory? In this case, if we schedule SCPs automatically, there will be data loss. In this scenario, regardless of what we do, there will be dataloss unless the correct WAL directory is (again) specified. In fact, I don't believe you can change WAL dir without restarting servers (I also don't think it works with rolling restart). I don't think this is a valid scenario for this issue. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
