Operating HBase – Things You Need to Know
Christian Gügi
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Outline● HBase internals
● Overview of HBase utilities
● HBase split visualisation with Hannibal
● Challenges & lessons learned
● Resources to get started
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About me● Software Architect @ Sentric
● Founder and organizer of the Swiss Big Data User Grouphttp://www.bigdata-usergroup.ch
● Contact:[email protected]://www.sentric.ch@chrisgugi
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HBase Internals
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Data Model● A sparse, multi-dimensional, sorted map
● Table consist of rows, each has a row key
● Each row may have any number of columns
● Rows are sorted lexicographically based on row key
● Column = Column Family : Column Qualifier
– Cell → {rowkey, column, timestamp}
● Region: contiguous set of sorted rows
● Region: unit of distribution and availability
[Bigtable: A Distributed Storage System for Structured Data]
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Physical Data Organization
Memstore
HFile(on HDFS)
HFile(on HDFS)
Store
Region
HLo
g(W
AL
on H
FD
S)
content Column Family
● Column families are stored separately on disk
– Unit of access control with different patterns
● Writes are held (sorted) in memory until flush
● Sorted on disk in predictable order
– By row key, column key, descending timestamp
Memstore
HFile(on HDFS)
Store
anchor Column Family
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Flushes and Compaction● Flushing/compaction per Region
– One thread (CompactSplitThread) per region server
● Minor compaction
– Merges two or more HFiles into one
● Major compaction
– Picks up all HFiles in the region, merges them and removes deleted k/v
● Regions are split when grown too large
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System Architecture
Master
HBase
Write-Ahead Log
RegionServer
HDFS ZooKeeper
[HBase: The Definitive Guide]
API
MemstoreHFile
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Key Design & Distribution● Bad idea: continuous number or timestamp
(sequential row keys)– RegionServer hot-spotting
● Better: use hash function and/or composite key – Distribute keys over random regions
– Uniform reads/writes across key space
● Proper key design is very essential– E.g. reversed URL (Bigtable paper)
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Overview HBase Utilities
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Useful Tools● hbck – checks and fixes table integrity and
region consistency
● HFile – examine contents of HFile
● HLog – examine contents of HLog file
● OfflineMetaRepair – rebuild meta table from file system
● HBase web interfaces– Master
– RegionsServer
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Monitoring Tools● Ganglia
● Nagios
● OpenTSDB
● …
All tools use metrics provided through JMX
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Manual Splitting● Via master web interface– Split
● HBase shell split command
● RegionSplitter– Create table with pre-split regions
– Rolling split of all regions on existing table
– . /bin/hbase org.apache.hadoop.hbase.util.RegionSplitter
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Disable Automatic Splitting● Determined by hbase.hregion.max.filesize
● Set to max. 100GB
● OK, but: – How do I monitor my region growth?
– Where do I split when I have irregular data growth?
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HBase Split Visualisation with Hannibal
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Hannibal● Open source, project on github
– https://github.com/sentric/hannibal
● Web based
● Implemented in Scala
● Compatible with HBase 0.90
● Support > 0.92 added soon
● Check it out!
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How well are regions balanced over the cluster?
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How well are the regions split for the table?
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How did the region evolve over time?
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Future Plans● HBase 0.92 client API changes allow to
query Compaction-State on Regions through HBaseAdmin → differentiate major from minor compactions
● Add tool to find best region-key for irregular data growth
● Expose metrics through JMX
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Challenges & Lessons Learned
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Challenges● Everyone is still learning
● Some issues only appear at scale– At scale, nothing works as advertised
● Production cluster configuration– Hardware issues
– Tuning cluster configuration to our work loads
● HBase stability
● Monitoring health of HBase
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Lessons Learned● Schema & key design
– What’s queried together should be stored together
● Monitoring/Operational tooling is most important
● Forget “emergency actions”, it takes some time
● You need DevOps in production
● Huge know-how curve, you need to know the whole ecosystem
– Hadoop, HDFS, Map/Red, ZooKeeper
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Resources to get started● https://github.com/sentric/hannibal
● http://hbase.apache.org/book.html
● https://github.com/jmhsieh/hbase-repair-scripts
● http://www.sentric.ch/blog/best-practice-why-monitoring-hbase-is-important
● HBase: The Definitive Guide
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Questions?@chrisgugi
Thank you!
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