Optimizing_hbase_scanner_performance

2. Optimizing HBase scanner
performance
Mikhail Bautin
Software Engineer
01/19/2012

3. HBase Scanners
What happens on a Get
RegionScanner
ColumnFamily1 ColumnFamily2
Store = (Region,
StoreScanner StoreScanner CF)
...
StoreFileScanne StoreFileScanne StoreFileScanne
...
r r r
(R1,C1,T3) (R1,C2,T2) (R1,C1,T1) (R1,C2,T3) (R2,C2,T1) . . .
(R1,C2,T1) (R2,C1,T2)

4. HBase Scanner State
What happens on a next()
RegionScanner
ColumnFamily1 Priority ColumnFamily2
Queue
Store = (Region,
StoreScanner StoreScanner CF)
Priority Priority
Queue ... Queue
StoreFileScanne StoreFileScanne StoreFileScanne
...
r r r
Current KeyValue Current KeyValue Current KeyValue

5. Avoiding next() on StoreFileScanner
Every next() call may result in disk I/O
▪ HBASE-4433: avoid extra next if done with row/column
(Kannan)
▪ An optimization for queries specifying a column set
▪ INCLUDE_AND_SEEK_NEXT_COL
▪ INCLUDE_AND_SEEK_NEXT_ROW
▪ HBASE-4434: Don't do HFile Scanner next() unless the next
KV is needed (Kannan)
▪ Avoid aggressive pre-fetching

6. Simple ROWCOL Bloom Filters
Do we have to read all of these files?
Query: (R1, C3)
Row Col TS Row Col TS Row Col TS
T2 C1 T3 C1 T4
C1 R1
R1 T1 R1 C2 T3 C2 T2
C2 T1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2
T2 C2 T3
R2 C2
T1
C3 T1

7. Simple ROWCOL Bloom Filters
In some cases, we only have to read one file
Query: (R1, C3)
Row Col TS
R1 C1 T3
R1 C2 T3
R1 C3 T2
C1 T2
R2
C2 T3

8. Multi-column Bloom Filters (HBASE-2794)
ROWCOL Bloom filters for multi-column queries
Query: C1 and C3 in all rows
Row Col TS Row Col TS Row Col TS
T2 C1 T3 C1 T4
C1 R1
R1 T1 R1 C2 T3 C2 T2
C2 T1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2
T2 C2 T3
R2 C2
T1
C3 T1

9. Multi-column Bloom Filters (HBASE-2794)
ROWCOL Bloom filters for multi-column queries
Query: C1 and C3 in all rows—seek to (R1,
C1)
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C1 T1 R1 C2 T3 R1 C2 T2
R1 C2 T1 R1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2
T2 C2 T3
R2 C2
T1
C3 T1

10. Multi-column Bloom Filters (HBASE-2794)
ROWCOL Bloom filters for multi-column queries
Query: C1 and C3 in all rows—seek to (R1,
C3)
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2 R2 C1 T1
C1 T1 C1 T2 Fake key: (R1, end of
R2 C3)
T2 C2 T3
R2 C2
T1
C3 T1
Fake key: (R1, end of
C3)

11. Multi-column Bloom Filters (HBASE-2794)
ROWCOL Bloom filters for multi-column queries
Query: C1 and C3 in all rows—seek to (R2,
C1)
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2
R2 C1 T2
R2 C2 T2 R2 C2 T3
R2 C2 T1 (R2, C1, T2)
R2 C3 T1 wins by
timestamp

12. Multi-column Bloom Filters (HBASE-2794)
ROWCOL Bloom filters for multi-column queries
Query: C1 and C3 in all rows—seek to (R2,
C3)
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2
R2 C1 T2 Fake key: (R2, end of
C3)
Fake key: (R2, end of
R2 C3 T1
C3)
(R2, C3,
T1)

13. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
T2 C1 T3 C1 T4
C1 R1
R1 T1 R1 C2 T3 C2 T2
C2 T1 C3 T2 R2 C1 T1
C1 T1 C1 T2 Fake key: (R1, C1,
R2 T4)
T2 C2 T3
R2 C2
T1 Fake key: (R1, C1,
C3 T1
T3)
Fake key: (R1, C1,
T2)

14. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
T2 C1 T3 R1 C1 T4
C1
R1 T1 R1 C2 T3 R1 C2 T2
C2 T1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2 (R1, C1, T4)
T2 C2 T3
R2 C2
T1 Fake key: (R1, C1,
C3 T1
T3)
Fake key: (R1, C1,
T2)

15. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2 R2 C1 T1
C1 T1 C1 T2 Fake key: (R1, C3,
R2 T4)
T2 C2 T3
R2 C2
T1 Fake key: (R1, C3,
C3 T1
T3)
Fake key: (R1, C3,
T2)

16. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2 (R2, C1, T1)
T2 C2 T3
R2 C2
T1 Fake key: (R1, C3,
C3 T1
T3)
Fake key: (R1, C3,
T2)

17. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2 (R2, C1, T1)
T2 C2 T3
R2 C2
T1 (R1, C3, T2) is
C3 T1 next
Fake key: (R1, C3,
T2)

18. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2 R2 C1 T1
C1 T1 C1 T2
R2 (R2, C1, T1)
T2 C2 T3
R2 C2
T1 Fake key: (R2, C1,
T3)
C3 T1
To be selected next.
Fake key: (R2, C1,
T2)

19. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2
C1 T1 R2 C1 T2
(R2, C1, T1)
T2 R2 C2 T3
R2 C2
T1 (R2, C1, T2)
C3 T1
wins by
timestamp
Fake key: (R2, C1,
T2)

20. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2
C1 T1 R2 C1 T2 Fake key: (R2, C3,
T2 R2 C2 T3
T4)
R2 C2
T1 Fake key: (R2, C3,
T3)
C3 T1
Fake key: (R2, C3,
T2)

21. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2
C1 T1 R2 C1 T2 EO
F
T2 R2 C2 T3
R2 C2
T1
Real seek to
C3 T1
(R2, C3, T3)
Fake key: (R2, C3,
T2)

22. Lazy Seek (HBASE-4465)
Optimizing for reading recent data
T1 – T2 – T1 –
T2 T3 T4
Row Col TS Row Col TS Row Col TS
R1 C1 T4
R1 C3 T2
R2 C1 T2 EO
F
EOF
R2 C3 T1
(R2, C3,
T1)

23. Top-of-the-row seek
Some applications do not use DeleteFamily
▪ We always seek to the top of the row first
▪ DeleteFamily comes before all columns, i.e. at (R1, empty column)
▪ Even if we only need (R1, C1), there might be a DeleteFamily for R1
▪ Some applications do not even use DeleteFamily
▪ Two fixes by Liyin Tang:
▪ Utilize existing ROWCOL Bloom filter (HBASE-4469)
▪ Added a separate ROW-only Bloom filter for DeleteFamily(HBASE-
4532)

24. Seek on deleted KV (HBASE-4585)
What if the requested column has been deleted?
▪ We are requesting C1, C2, ..., Cn
▪ What if we see a delete marker for Ci?
▪ Previously, we would keep calling next()
▪ Now, we seek to (i + 1)’th requested column
(also a fix by Liyin)

25. Data block read requests (dark launch)
Thu, Sep 15 – Sun, Sep 25 2011
Fri Sep 16th vs. Sep 23rd:
45% savings in logical
block read requests
(cache hits + misses)
Pushed on Tue Sep 20th:
• No extra next when done with
column/row (HBASE-4433)
• No KV prefetch (HBASE-4434)
• Lazy Seek (HBASE-4465)

26. Data block read requests (dark launch)
Sun, Sep 25 – Mon, Oct 3 2011
Sun Sep 25th vs. Oct 2nd:
33% savings in logical
block read requests
(cache hits + misses)
Pushed on Fri Sep 30th:
• Avoid top-of-the-row seek
(HBASE-4469, Liyin)
• Off-peak compactions (HBASE-
4463, Karthik)

27. Data block cache misses (dark launch)
▪ 20.6 K (Mon Sep 19th) -> 11.8 K (Mon Sep 26th) -> 9.8 K (Mon
Oct 3rd)
▪ 52% savings (42% and then 17% more)
• No next KV prefetch
• No next() when done
with row/column • No top-of-the-row seek
• Lazy Seek • Off-peak compactios

28. Avoid loading previous block (HBASE-4443)
We sometimes go to previous block on exact match
▪ Future work
▪ Suppose the first key of a block matches (Row, Column)
▪ But maybe there is an earlier key that would also match?
▪ We load the previous block to find out
▪ Possible fixes:
▪ Track deletes and optimize the MAX_VERSIONS=1 case
▪ Add last key in block to index (increases index size)

29. Top-of-the-column seek (HBASE-4962)
Some applications do not use DeleteColumn
▪ Future work
▪ DeleteColumn deletes all versions of a particular column
▪ Comes before all Puts for a (Row, Column)
▪ Slows down timestamp range queries
▪ Proposed solution:
▪ Add a (Row, Column) Bloom filter for DeleteColumn only
▪ Seek to (Row, Column, T2) for a [T1, T2] range query

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