My organization is looking at making some changes that would introduce HBase bulk loads that write into a remote cluster. Today our bulk loads write to a local HBase. By local, I mean the home directory of the user preparing and executing the bulk load is on the same HDFS filesystem as the HBase cluster. In the remote cluster case, the HBase being loaded to will be on a different HDFS filesystem.
The thing I am wondering about is what the best pattern is for determining the location to write HFiles to from the job preparing the bulk load. Typical examples write the HFiles somewhere in the user's home directory. When HBase is local, that works perfectly well. With remote HBase, it can work, but results in writing the files twice: once from the preparation job and a second time by the RegionServer when it reacts to the bulk load by copying the HFiles into the filesystem it is running on. Ideally the preparation job would have some mechanism to know where to write the files such that they are initially written on the same filesystem as HBase itself. This way the bulk load can simply move them into the HBase storage directory like happens when bulk loading to a local cluster. I've considered a pattern where the bulk load preparation job reads the hbase.rootdir property and pulls the filesystem off of that. Then, it sticks the output in some directory (e.g. /tmp) on that same filesystem. I'm inclined to think that hbase.rootdir should only be considered a server-side property and as such I shouldn't expect it to be present in client configuration. Under that assumption, this isn't really a workable strategy. It feels like HBase should have a mechanism for sharing a staging directory with clients doing bulk loads. Doing some searching, I ran across "hbase.bulkload.staging.dir", but my impression is that its intent does not exactly align with mine. I've read about it here [1]. It seems the idea is that users prepare HFiles in their own directory, then SecureBulkLoad moves them to "hbase.bulkload.staging.dir". A move like that isn't really a move when dealing with a remote HBase cluster. Instead it is a copy. A question would be why doesn't the job just write the files to "hbase.bulkload.staging.dir" initially and skip the extra step of moving them? I've been inclined to invent my own application-specific Hadoop property to use to communicate an HBase-local staging directory with my bulk load preparation jobs. I don't feel perfectly good about that idea though. I'm curious to hear experiences or opinions from others. Should I have my bulk load prep jobs look at "hbase.rootdir" or "hbase.bulkload.staging.dir" and make sure those get propagated to client configuration? Is there some other mechanism that already exists for clients to discover an HBase-local directory to write the files? [1] http://hbase.apache.org/book.html#hbase.secure.bulkload
