tapdb: switch proof cache to size-based limits and add deep size estimation

[ffranr]

Issue: #1865

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This PR introduces a size-based proof cache and supporting deep-size logic.

Summary

• Replace proof-count cache limits with a byte-size limit.
• Add human-readable size parsing in configuration.
• Introduce deep size estimation (LowerBoundByteSize) and apply it to proof cache entries.
• Update proof cache keys for finer-grained eviction.
• Improve error handling and logging around cache initialization.

Note

It's pretty trivial to get from here to logging cache size, but we need lightninglabs/neutrino#330 for that.

[gemini-code-assist]

Summary of Changes

Hello @ffranr, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refactors the tapdb proof caching mechanism by transitioning from a simple count-based eviction strategy to a more sophisticated size-based approach. This change aims to provide more efficient and predictable memory usage for the proof cache. It introduces a robust deep size estimation utility for Go objects and updates the configuration to be more user-friendly with human-readable size inputs. Additionally, cache keying and management logic have been refined for better performance and error handling.

Highlights

• Size-Based Proof Cache: The proof cache now uses a byte-size limit instead of a count-based limit, allowing for more accurate memory management. The default size is set to 32MB.
• Deep Size Estimation: A new utility function, LowerBoundByteSize, has been introduced in the fn package to provide a conservative deep-size estimate of Go objects, including handling pointers and cycles. This is crucial for the new size-based cache.
• Human-Readable Configuration: The configuration for the maximum proof cache size now accepts human-readable values like '32MB' or '1GB', improving user experience.
• Finer-Grained Cache Eviction: The proof cache keys have been updated to UniverseProofKey, which combines the universe ID and leaf key, enabling more granular eviction of cached proofs.
• Improved Error Handling and Logging: Error handling around MultiverseStore initialization has been enhanced, and logging messages for cache operations have been made more descriptive.

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[gemini-code-assist]

Code Review

This pull request introduces a significant improvement by switching the proof cache from count-based to size-based limits, incorporating deep size estimation for more accurate memory management. The changes also include finer-grained eviction strategies for cache entries and enhanced error handling and logging around cache initialization. The new LowerBoundByteSize function, utilizing reflect and unsafe, provides a conservative estimate of an object's memory footprint, which is crucial for the new cache mechanism. Comprehensive unit tests have been added for this new functionality, covering various data types and edge cases like pointer cycles. Configuration options have been updated to support human-readable size values for the cache limit. Overall, the changes align well with the stated objective of improving cache efficiency and control.

[coveralls]

Pull Request Test Coverage Report for Build 19179362473

Details

• 178 of 199 (89.45%) changed or added relevant lines in 6 files are covered.
• 95 unchanged lines in 25 files lost coverage.
• Overall coverage increased (+0.03%) to 56.558%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tapcfg/server.go	2	4	50.0%
tapdb/multiverse.go	12	14	85.71%
fn/memory.go	89	93	95.7%
tapdb/multiverse_cache.go	66	79	83.54%

Files with Coverage Reduction	New Missed Lines	%
commitment/tap.go	1	85.65%
fn/context_guard.go	1	91.94%
proof/courier.go	1	78.88%
tapdb/interfaces.go	1	86.67%
tapdb/multiverse_cache.go	1	91.37%
asset/group_key.go	2	72.15%
mssmt/compacted_tree.go	2	78.57%
tapdb/mssmt.go	2	90.45%
tapdb/multiverse.go	2	80.69%
tapdb/sqlc/transfers.sql.go	2	83.33%

Totals
Change from base Build 18942913401:	0.03%
Covered Lines:	64443
Relevant Lines:	113942

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💛 - Coveralls