Bw-Tree Update Implementation

1. Scalable Computing Systems Laboratory
Hanyang University
Update Change
1

2. 2
Existing Update Method
1. TraverseReadOptimized() to check old & new value's existence
2. Traverse() to locate leaf node to insert 'delete delta'
3. update Mapping Table using CAS operation
4. Traverse() to locate leaf node to insert 'insert delta'
5. update Mapping Table using CAS operation
① TraverseReadOptimized()
Node R

3. 3
Existing Update Method
1. TraverseReadOptimized() to check old & new value's existence
2. Traverse() to locate leaf node to insert 'delete delta'
3. update Mapping Table using CAS operation
4. Traverse() to locate leaf node to insert 'insert delta'
5. update Mapping Table using CAS operation
② Traverse()
If <key, oldVal> does not exist:
update() returns false
Node R

4. PID Ptr
L
P
R
S
4
Existing Update Method
Δ
Δ delete
Node R
③ CAS
1. TraverseReadOptimized() to check old & new value's existence
2. Traverse() to locate leaf node to insert 'delete delta'
3. update Mapping Table using CAS operation
4. Traverse() to locate leaf node to insert 'insert delta'
5. update Mapping Table using CAS operation
Node R

5. 5
Existing Update Method
Δ
Δ delete
PID Ptr
L
P
R
S
Node R
1. TraverseReadOptimized() to check old & new value's existence
2. Traverse() to locate leaf node to insert 'delete delta'
3. update Mapping Table using CAS operation If CAS failed: repeat ② ~ ③
4. Traverse() to locate leaf node to insert 'insert delta'
5. update Mapping Table using CAS operation
Node R
③ CAS

6. 6
Existing Update Method
1. TraverseReadOptimized() to check old & new value's existence
2. Traverse() to locate leaf node to insert 'delete delta'
3. update Mapping Table using CAS operation
4. Traverse() to locate leaf node to insert 'insert delta'
5. update Mapping Table using CAS operation
④ Traverse()
If <key, newVal> exists:
update() assert fails
Node R

7. PID Ptr
L
P
R
S
7
Existing Update Method
Δ
Δ delete
Node R
1. TraverseReadOptimized() to check old & new value's existence
2. Traverse() to locate leaf node to insert 'delete delta'
3. update Mapping Table using CAS operation
4. Traverse() to locate leaf node to insert 'insert delta'
5. update Mapping Table using CAS operation If CAS failed: repeat ④ ~ ⑤
⑤ CAS Δ insert
Node R

8. PID Ptr
L
P
R
S
8
Existing Update Method
Δ
Δ delete
Node R
Δ insert
Node R
Problems
1. Operation is not atomic (2 CAS operations involved)
Any operation accessing <key, newVal> or <key, oldVal>
between first & second CAS will be failed.
2. Traverse() is called at least 3 times
All traverse() returns same node.

9. 9
Existing Update Method
Solutions
1. link Δ delete and Δ insert and use CAS only once to change Mapping Table.
2. Create new Traverse() that checks two <key, value> at once.
Problems
1. Operation is not atomic (2 CAS operations involved)
Any operation accessing <key, newVal> or <key, oldVal>
between first & second CAS will be failed.
2. Traverse() is called at least 3 times
All traverse() returns same node.
PID Ptr
L
P
R
S
Δ
Δ delete
Node R
Δ insert
Node R

10. 10
New Update Method
① NewTraverse()
Node R
1. Use NewTraverse() that returns two <key, val> pairs
There is 3 reason for update() to fail
1. NewTraverse() aborted, returning nullptr
2. <key, oldValue> does not exist
3. <key, newValue> already exist
2. Create Δdelete & Δinsert on top of base node without modifying Mapping Table
3. Use CAS operation to modify mapping table If CAS failed: repeat ① ~ ③

11. PID Ptr
L
P
R
S
11
New Update Method
Δ
Δ delete
Node R
Δ insert
Node R
② Create Δdelete & Δinsert
Two combined Δ work as one Δupda
1. Use NewTraverse() that returns two <key, val> pairs
There is 3 reason for update() to fail
1. NewTraverse() aborted, returning nullptr
2. <key, oldValue> does not exist
3. <key, newValue> already exist
2. Create Δdelete & Δinsert on top of base node without modifying Mapping Table
3. Use CAS operation to modify mapping table If CAS failed: repeat ① ~ ③

12. PID Ptr
L
P
R
S
12
New Update Method
Δ
Δ delete
Node R
Δ insert
Node R
③ CAS
1. Use NewTraverse() that returns two <key, val> pairs
There is 3 reason for update() to fail
1. NewTraverse() aborted, returning nullptr
2. <key, oldValue> does not exist
3. <key, newValue> already exist
2. Create Δdelete & Δinsert on top of base node without modifying Mapping Table
3. Use CAS operation to modify mapping table If CAS failed: repeat ① ~ ③

13. PID Ptr
L
P
R
S
13
New Update Method
Δ
Δ delete
Node R
Δ insert
Node R
③ CAS
Advantage
1. Update operation is atomic
only one CAS operation is performed
2. Traverse() is called only once per each CAS operation
Reducing redundant tree traversal

14. 14
New Update Method
362,785,060
127,015,726
835,6980 0 0
0
100000000
200000000
300000000
400000000
1 100 10000
#ofupdatefailure
# of update key
prev Update() new Update()
avg. failure of 5 tests (44threads, total 88000000 updates)
New Update() shows no failure what so ever.

15. Scalable Computing Systems Laboratory
Hanyang University
Thank You
15