Add MaxHeightSplay for the splay tree to improve its performance by reducing its skewness. #957
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To reduce the skewness of the splay tree, perform a MaxHeightSplay every sqrt(n) regular splays. To implement it, height attribute added to Node struct and splayCount and operationCount is added to Tree struct.
To test max heigt splay, ToTestString is updated to include node's height. Tests using ToTestString is updated and test for max height splay is added.
WalkthroughThe changes optimize the Splay tree implementation by incorporating enhancements to prevent skewness, thereby improving performance in the Changes
Sequence Diagram(s)sequenceDiagram
participant User
participant SplayTree
participant Node
User->>SplayTree: Insert Node
SplayTree->>Node: Create NewNode
Node->>Node: Initialize Height
SplayTree->>SplayTree: Update Height
SplayTree->>User: Return Tree Structure
Assessment against linked issues
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Review details
Configuration used: CodeRabbit UI
Review profile: CHILL
Files selected for processing (3)
- pkg/document/document_test.go (1 hunks)
- pkg/splay/splay.go (11 hunks)
- pkg/splay/splay_test.go (6 hunks)
Additional comments not posted (14)
pkg/splay/splay_test.go (4)
159-181: Add comprehensive checks in the "max height splay test".The new test case for max height splay is a valuable addition. Ensure that it comprehensively checks the tree's behavior and structure after each insertion.
59-65: Update assertions to reflect new node representation.The assertions have been updated to include an additional index in the node representation. Ensure that these changes correctly reflect the updated logic in the
ToTestString()method.Verification successful
Assertions correctly reflect the updated node representation.
The
ToTestStringmethod implementation confirms that the node representation includes weight, length, height, and value, matching the updated test assertions. No further action is needed.Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Description: Verify the correctness of the updated node representation in the ToTestString method. # Test: Check the ToTestString method implementation. Expect: The method includes the new index logic. ast-grep --lang go --pattern $'func (t *Tree[$_] ToTestString() string { $$$ }'Length of output: 690
Line range hint
124-146: Review range deletion tests for updated node representation.The range deletion tests have been updated to reflect the new node representation. Ensure that these changes are consistent with the updated tree logic.
Verification successful
Verification successful: Node representation in range deletion tests is consistent with updated tree logic.
The
ToTestStringmethod inpkg/splay/splay.goconstructs node representations using weight, value length, height, and value string, which matches the format expected in the test assertions. The changes in the range deletion tests reflect this updated logic correctly.Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Description: Verify the correctness of the updated node representation in the range deletion tests. # Test: Check the ToTestString method implementation. Expect: The method includes the new index logic. ast-grep --lang go --pattern $'func (t *Tree[$_] ToTestString() string { $$$ }'Length of output: 690
95-104: Ensure correctness of deletion tests with updated node representation.The test cases for deletion now expect a new node representation. Verify that these changes align with the updated logic in the tree implementation.
Verification successful
Deletion Tests Correctly Verify Updated Node Representation
The deletion tests in
pkg/splay/splay_test.gocorrectly use the updated node representation format in their assertions, ensuring alignment with theToTestStringmethod. The tests verify both the tree's string representation and node indices after deletions, confirming correctness.Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Description: Verify the correctness of the updated node representation in the deletion tests. # Test: Check the ToTestString method implementation. Expect: The method includes the new index logic. ast-grep --lang go --pattern $'func (t *Tree[$_] ToTestString() string { $$$ }'Length of output: 690
Script:
#!/bin/bash # Description: Check the deletion test cases to ensure they expect the correct node representation format. # Locate the test cases for deletion in the splay_test.go file. rg 'func Test.*Deletion' -A 20 pkg/splay/splay_test.goLength of output: 56
Script:
#!/bin/bash # Description: Search for all test functions in the splay_test.go file to find those related to deletion. # List all test functions in the splay_test.go file. rg '^func Test' -A 20 pkg/splay/splay_test.goLength of output: 845
Script:
#!/bin/bash # Description: Search for any usage of a Delete method or similar within the splay_test.go file to find deletion-related tests. # Search for the Delete method or similar operations in the test file. rg 'Delete' pkg/splay/splay_test.goLength of output: 302
Script:
#!/bin/bash # Description: Search for assertions following deletion operations to verify alignment with the updated node representation. # Search for assertions in the context of Delete operations. rg 'Delete' -A 5 pkg/splay/splay_test.go | rg 'assert\.Equal'Length of output: 337
pkg/splay/splay.go (9)
40-40: Add height field to Node struct for balancing operations.The addition of the
heightfield is crucial for implementing balancing operations. Ensure that this field is correctly initialized and updated throughout the code.
50-51: Initialize height in NewNode function.The
NewNodefunction now initializes the height to 1. Verify that this initialization is consistent with the intended logic for new nodes.
57-74: Implement leftHeight, rightHeight, and InitHeight methods.These methods are essential for managing node heights. Ensure they are correctly implemented and used in the tree operations.
117-119: Introduce operation counters in Tree struct.The
splayCountandoperationCountfields are introduced to manage splay operations. Ensure these counters are correctly incremented and reset.
155-156: Update height after insertion.The
UpdateHeightmethod is called after node insertion to maintain correct height values. Ensure this update is correctly integrated into the insertion logic.
Line range hint
161-206: Separate InternalSplay from public Splay method.The separation of
InternalSplayfromSplayhelps manage internal and public operations distinctly. Ensure that this separation is effectively utilized in the codebase.
197-206: Implement MaxHeightSplay logic in Splay method.The
Splaymethod now includes logic to perform aMaxHeightSplayevery √n operations. Verify that this logic is correctly implemented and aligns with the performance improvement objectives.
208-220: Implement MaxHeightSplay to reduce skewness.The
MaxHeightSplaymethod finds and splays the deepest node to reduce skewness. Ensure that the logic effectively identifies and splays the correct node.
322-334: Ensure UpdateHeight method correctly recalculates node height.The
UpdateHeightmethod recalculates node height based on children. Verify that this method is invoked appropriately throughout the tree operations.pkg/document/document_test.go (1)
135-150: Update assertions to reflect new array representation.The assertions for array operations have been updated to include additional indices in the representation. Ensure that these changes correctly reflect the updated logic in the
ToTestString()method.Verification successful
Ensure test assertions match the
ToTestStringformat.The
ToTestStringmethod inpkg/splay/splay.gooutputs a string with node weight, value length, height, and value string. Verify that the test assertions inpkg/document/document_test.goreflect this format accurately. Adjust the test outputs if necessary to align with the method's logic.Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Description: Verify the correctness of the updated array representation in the ToTestString method. # Test: Check the ToTestString method implementation. Expect: The method includes the new index logic. ast-grep --lang go --pattern $'func (t *Tree[$_] ToTestString() string { $$$ }'Length of output: 690
I had to update the test code because the ToTest String had to output including the height of the display tree.
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Files selected for processing (1)
- test/bench/document_bench_test.go (1 hunks)
Additional comments not posted (4)
test/bench/document_bench_test.go (4)
145-145: Verify the correctness ofToTestString()output.Ensure that the expected output string accurately reflects the internal state of the array after the operations. The indices and values should match the operations performed.
Verification successful
Verification of
ToTestString()output is consistent with expected behavior.The
ToTestString()function is used to output a string containing the metadata of the elements for debugging purposes. The expected output in the test assertion appears to accurately reflect the internal state of the array, including indices and values, as intended by the function. No issues found with the test assertion.
- The
ToTestString()function is defined inpkg/document/crdt/array.goand outputs metadata for debugging.Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Description: Verify the correctness of the expected output for `ToTestString()`. # Test: Search for `ToTestString()` implementations to understand its output format. ast-grep --lang go --pattern $'func ToTestString() string { $$$ }'Length of output: 67
Script:
#!/bin/bash # Description: Search for the definition or documentation of `ToTestString()` using ripgrep. # Search for `ToTestString` in the codebase to locate its definition or related comments. rg 'ToTestString' --context 5Length of output: 33501
160-160: VerifyToTestString()output after second insertion.Check that the expected output string correctly represents the array's state after the second insertion operation. The indices and values should be consistent with the operations performed.
155-155: VerifyToTestString()output after insertion.Ensure that the expected output string accurately reflects the array's state after an integer is inserted. The indices and values should match the insertion operation.
150-150: VerifyToTestString()output after deletion.Check that the expected output string correctly represents the array's state after an element is deleted. The indices and values should be consistent with the deletion operation.
If the number of operations is less than 10,000, performing max_height_splay too frequently can degrade performance. To prevent this, only perform max_height_splay when the number of operations exceeds 10,000.
The test cases have been updated due to changes in max-height splay, which is no longer performed when the operation count is 10,000 or less.
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Files selected for processing (1)
- pkg/splay/splay_test.go (6 hunks)
Files skipped from review as they are similar to previous changes (1)
- pkg/splay/splay_test.go
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I’ve decided to close this PR as further research is required. The code applying max height splay caused a stack overflow during benchmarking, and I need to analyze the cause in more detail. In addition, I found a test case that works inefficiently because the new implementation method calls the max height display function first and then the display. Given these issues, I see a strong need for benchmarking code that can compare the new implementation with the existing one. I will prioritize this task first, and once all concerns are fully resolved, I will submit a new PR. |
What this PR does / why we need it:
Why this is needed:
Currently, the crdt.Text data structure uses a Splay tree. While Splay trees are efficient for performing operations in a continuous range, they have a downside where consecutively inserted elements may become linearly arranged in the tree, leading to a skew tree. When performing M operations on a tree with N nodes, the performance is generally guaranteed to be O((N+M) log N). However, if the tree becomes skewed, each operation might initially take O(N) time, though it could eventually improve. This skewness can degrade the performance of the crdt.Text data structure, making it crucial to explore ways to prevent this skewness and maintain the tree's performance and efficiency. This PR aims to address the performance and efficiency degradation in the crdt.Text data structure caused by skewness in the Splay tree.
What this PR does:
In this Pull Request, we introduce a method called max_height_splay to reduce the skewness. This method involves finding the deepest leaf node and performing a splay operation on it every √n operations, where n is the number of splay operations performed. The time complexity of max_height_splay is also amortized O(log n), similar to other operations. A POC for this approach was implemented in C++, and the code can be found here.
Which issue(s) this PR fixes:
Fixes #941
Special notes for your reviewer:
If operations are primarily occurring at the end of the document, performance degradation might still occur. Although this may require further research, it seems worthwhile to implement as it can provide good performance in most cases.
I have added test code but did not include benchmark code. If you think it's needed, please mention me! And while adding the test code, I needed to check the height of the Splay tree nodes, which led to some modifications in other test code as well.
Does this PR introduce a user-facing change?:
Additional documentation:
Checklist:
Summary by CodeRabbit
New Features
Bug Fixes
Tests