David Witten created HBASE-10216:
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Summary: Change HBase to support local compactions
Key: HBASE-10216
URL: https://issues.apache.org/jira/browse/HBASE-10216
Project: HBase
Issue Type: New Feature
Components: Compaction
Environment: All
Reporter: David Witten
As I understand it compactions will read data from DFS and write to DFS. This
means that even when the reading occurs on the local host (because region
server has a local copy) all the writing must go over the network to the other
replicas. This proposal suggests that HBase would perform much better if all
the reading and writing occurred locally and did not go over the network.
I propose that the DFS interface be extended to provide method that would merge
files so that the merging and deleting can be performed on local data nodes
with no file contents moving over the network. The method would take a list of
paths to be merged and deleted and the merged file path and an indication of a
file-format-aware class that would be run on each data node to perform the
merge. The merge method provided by this merging class would be passed files
open for reading for all the files to be merged and one file open for writing.
The custom class provided merge method would read all the input files and
append to the output file using some standard API that would work across all
DFS implementations. The DFS would ensure that the merge had happened properly
on all replicas before returning to the caller. It could be that greater
resiliency could be achieved by implementing the deletion as a separate phase
that is only done after enough of the replicas had completed the merge.
HBase would be changed to use the new merge method for compactions, and would
provide an implementation of the merging class that works with HFiles.
This proposal would require a custom code that understands the file format to
be runnable by the data nodes to manage the merge. So there would need to be a
facility to load classes into DFS if there isn't such a facility already. Or,
less generally, HDFS could build in support for HFile merging.
The merge method might be optional. If the DFS implementation did not provide
it a generic version that performed the merge on top of the regular DFS
interfaces would be used.
It may be that this method needs to be tweaked or ignored when the region
server does not have a local copy data so that, as happens currently, one copy
of the data moves to the region server.
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