This document discusses tuning Garbage First Garbage Collector (G1GC) for HBase clusters. Out of the box G1GC can hurt performance with long GC pauses. The key tuning parameters are heap size, initiating heap occupancy percentage, Eden size percentage, and HBase memory configuration caps. Tuning involves setting these parameters based on historical maximums for block cache size, memstore size, and static index size plus a buffer. Tuning Eden size also considers percentage time in GC and average young GC pause times. Adjustments may be needed over time based on cluster usage. Suboptimal client usage could also impact GC and requires fixing. Monitoring GC metrics helps evaluate tuning effectiveness.

1. HBase @ HubSpot

2. Multitenancy

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What does Multitenancy Mean?

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Benefits of Multitenancy

5. Identifying Bad Actors

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Our Tool: HBasetracing

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Ad-hoc Querying with HBasetracing

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HBasetracing Roll-up

9. Example Incident

10. Dealing with Bad Actors

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Quotas

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HADOOP_USER_NAME
Deploying Quotas

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When Quotas Help

14. Remember this?

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When Quotas Fall Flat

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Detention Queues

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The Dream

18. Handling Failure &
Managing Risk

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Read Replicas

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● Consistency.TIMELINE
● isStale()
Read Replica Usage

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Read Replica Timeout Settings

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Read Replica Limitations

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Cluster Replication

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Failover Client

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@StaleReadOnly Annotation

26. Monitoring

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31. G1GC:
Making it work with HBase

32. Why G1GC?
● Designed for large heaps.
○ Divides heap into many smaller G1 regions.
○ G1 regions scanned and collected independently.
● Instead of occasional very long pauses,
G1GC has more frequent, shorter pauses.
If tuned properly, G1GC can provide performant GC
that scales well for large RegionServer heaps.

33. The Need for Tuning
Out of the box, G1GC hurt our HBase
clusters’ performance:
● Too much time spent in GC pauses.
● Occasional very long GC pauses.
● “To-space Exhaustion”, leading to Full GCs,
which led to slow RegionServer deaths.

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Recommended Defaults

36. Important Metrics for Tuning
● G1GC Eden & Tenured size.
○ GC logs: “[Eden: … Survivors: … Heap: …]”
● HBase memory used by Memstore.
○ RegionServer JMX: “memStoreSize”
● HBase memory used by Block Cache.
○ RegionServer JMX: “blockCacheSize”
● HBase memory used by “static index”.
○ RegionServer JMX: “staticIndexSize”

37. Necessary Tuning Params
● JVM args:
-Xms, -Xmx
-XX:G1NewSizePercent
-XX:InitiatingHeapOccupancyPercent (aka “IHOP”)
● HBase configs (hbase-site.xml):
hfile.block.cache.size
hbase.regionserver.global.memstore.size

38. Necessary Tuning: Method
A. Find max block cache size, memstore size,
and static index size from the past month.
B. Sum 110% of (A) maxes, add heap waste.
C. Set IHOP and heap size such that Initiating
Heap Occupancy > (B) by at least 10% heap.
D. Ensure IHOP + G1NewSizePercent < 90%.
– 90% = 100% - G1ReservePercent (default 10)

39. Necessary Tuning: cont.
In hbase-site.xml:
● Set hfile.block.cache.size ratio value to 110%
max block cache size from the past month.
● Set hbase.regionserver.global.memstore.size
ratio value to 110% max Memstore size from
the past month.

42. Further Tuning & Considerations
● -XX:G1ReservePercent
○ Accommodating for burst-y usage.
● -XX:G1HeapRegionSize
○ Reducing occurrence of humongous objects.
○ Reducing long tail of slow GCs in some cases.
● -XX:G1NewSizePercent
○ Tuning individual pause time vs. % time in GC.

43. HBase Usage & Tuning Limits
A Full GC isn’t necessarily G1GC’s fault. There’s
a level of “bad usage” that’s unreasonable to
tune around:
● Unexpected, excessively burst-y traffic.
● Too many/enormous Humongous objects.
In either of these cases, the real solution is to
fix the client code.

44. Usage Note: Caching isn’t Free!
Yellow: % time spent in Mixed GC (left axis) | Blue: block cache churn, MB/sec (right axis)

45. ...to Summarize:
● Tune heap size, IHOP, & HBase memory
caps based on HBase memory usage.
● Tune Eden size based on % time in GC &
average Young GC pause times.
● Make adjustments as needed, based on
cluster usage.
● Look for suboptimal usage in your HBase
clients to further improve HBase GC.

46. Links & Reference
Blog Post — http://bit.ly/hbasegc
G1GC CollectD Plugin — http://bit.ly/collectdgc
G1GC Log Visualizer — http://bit.ly/gclogviz