Thiruvel Thirumoolan created HBASE-20643:
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Summary: Getting HDFSBlockDist in Master by querying RegionServers
Key: HBASE-20643
URL: https://issues.apache.org/jira/browse/HBASE-20643
Project: HBase
Issue Type: Improvement
Components: Balancer
Reporter: Thiruvel Thirumoolan
Assignee: Thiruvel Thirumoolan
Fix For: 2.1.0, 1.5.0, 1.4.5
Region locality information is needed by the balancer to generate region plans.
Computing HDFSBlockDistribution is expensive on larger clusters and adds load
to the NameNode. This also needs to be recomputed on a master restart. The
proposal is to get the HDFSBlockDistribution from the RegionServers instead of
computing it in Master. RS already has this information and we could just reuse
it by querying it. RS already passes dataLocality info via RegionLoad today.
Proposed Implementation: This is a high-level overview.
# A RegionServer API has to be added which will return HDFSBlockDistribution
for all the regions it hosts. RS already has this info. Since ClusterStatus has
already become bulky and we don’t need updated locality so fast, it’s better to
have another API rather than add this to RegionLoad and pass it along with
RSReport.
# Master will have a Chore to query all RegionServers and will cache the
HDFSBlockDistribution for those regions. This is easy and quick. Admins can
tune the frequency based on size of the cluster. On a ~90 nodes cluster with
500k regions and a prototype implementation and no load, it took about 5
seconds to get all HDFSBlockDistribution from RS.
# The cache will be an extension of RegionLocationFinder (subclass), if needed
to keep the implementation simple. Probably will get clear with implementation.
# Balancer will use the new cache to get all HDFSBlockDistribution. If there is
a new region and Chore didn’t get the block distribution from RS during its
previous run, then it will be computed by RegionLocationFinder the same way it
has been done now. If the Chore runs more frequently like every hour, then this
recomputation will be drastically reduced.
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