Andrew Kyle Purtell created HBASE-24637:
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Summary: Filter SKIP hinting regression
Key: HBASE-24637
URL: https://issues.apache.org/jira/browse/HBASE-24637
Project: HBase
Issue Type: Bug
Components: Filters, Performance, Scanners
Reporter: Andrew Kyle Purtell
I have been looking into reported performance regressions in HBase 2 relative
to HBase 1. Depending on the test scenario, HBase 2 can demonstrate
significantly better microbenchmarks in a number of cases, and usually shows
improvement in whole cluster benchmarks like YCSB.
To assist in debugging I added methods to RpcServer for updating per-call
metrics that leverage the fact it puts a reference to the current Call into a
thread local and that all activity for a given RPC is processed by a single
thread context. I then instrumented ScanQueryMatcher (in branch-1) and its
various friends (in branch-2.2), StoreScanner, HFileReaderV2 and HFileReaderV3
(in branch-1) and HFileReaderImpl (in branch-2.2), HFileBlock, and
DefaultMemStore (branch-1) and SegmentScanner (branch-2.2). Test tables with
one family and 1, 5, 10, 20, 50, and 100 distinct column-qualifiers per row
were created, snapshot, dropped, and cloned from the snapshot. Both 1.6 and 2.2
versions under test operated on identical data files in HDFS. For tests with
1.6 and 2.2 on the server side the same 1.6 PE client was used, to ensure only
the server side differed.
The results for pe --filterAll were revealing. See attached.
It appears a refactor to ScanQueryMatcher and friends has disabled the ability
of filters to provide meaningful SKIP hints, which disables an optimization
that avoids reseeking, leading to a serious and proportional regression in
reseek activity and time spent in that code path. So for queries that use
filters, there can be a substantial regression.
Other test cases that did not use filters did not show this regression. If
filters are not used the behavior of ScanQueryMatcher between 1.6 and 2.2 was
almost identical, as measured by counts of the hint types returned, whether or
not column or version trackers are called, and counts of store seeks or
reseeks. Regarding micro-timings, there was a 10% variance in my testing and
results generally fell within this range, except for the filter all case of
course.
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