perf: Optimize statCache expiration timestamp by using int64 instead of time.Time

[vedantdas-source]

Description

In the StatCache the entry struct tracks TTL expiration using a standard Go time.Time object. This time.Time struct consumes 24 bytes of memory which can be reduced to 8 bytes using int64 for the expiration timestamp. This saves 16 bytes of memory per object.

Changes Made

• Changed expiration field in the internal cache entry from time.Time to int64
• Cache insertion methods (Insert, InsertImplicitDir, AddNegativeEntry, etc.) now convert the incoming expiration time.Time parameter to seconds using .Unix()
• Lookup methods now evaluate expiration against now.Unix()

Benchmarking results

Using time.Time :

goos: linux
goarch: amd64
pkg: github.com/googlecloudplatform/gcsfuse/v3/internal/cache/metadata
cpu: Intel(R) Xeon(R) CPU @ 2.60GHz
BenchmarkStatCache_Insert-48                     3033651               409.2 ns/op           272 B/op          4 allocs/op
BenchmarkStatCache_AddNegativeEntry-48           7874757               149.2 ns/op            80 B/op          2 allocs/op
BenchmarkStatCache_LookUp-48                    19632806                61.15 ns/op           17 B/op          0 allocs/op

Using int64 :

goos: linux
goarch: amd64
pkg: github.com/googlecloudplatform/gcsfuse/v3/internal/cache/metadata
cpu: Intel(R) Xeon(R) CPU @ 2.60GHz
BenchmarkStatCache_Insert-48                     3174098               382.8 ns/op           256 B/op          4 allocs/op
BenchmarkStatCache_AddNegativeEntry-48           8443263               141.3 ns/op            64 B/op          2 allocs/op
BenchmarkStatCache_LookUp-48                    22825635                54.30 ns/op           11 B/op          0 allocs/op

All existing tests pass successfully.

Link to the issue in case of a bug fix.

Testing details

1. Manual - NA
2. Unit tests - Added stat_cache_benchmark_test.go to measure memory and CPU performance of StatCache operations.
3. Integration tests - NA

Any backward incompatible change? If so, please explain.

[gemini-code-assist]

Code Review

This pull request optimizes the entry struct in stat_cache.go by changing the expiration field from time.Time to int64 (using Unix timestamps) and adds a benchmark test suite to measure cache performance. The reviewer suggests using UnixMilli() instead of Unix() across all insertions and lookups to preserve sub-second precision while still maintaining the memory benefits of the int64 representation.

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.68%. Comparing base (b61c988) to head (f2acd33).

Files with missing lines	Patch %	Lines
internal/cache/metadata/stat_cache.go	62.50%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4857       +/-   ##
===========================================
+ Coverage        0   83.68%   +83.68%     
===========================================
  Files           0      170      +170     
  Lines           0    20958    +20958     
===========================================
+ Hits            0    17539    +17539     
- Misses          0     2762     +2762     
- Partials        0      657      +657     

Flag	Coverage Δ
unittests	83.68% <62.50%> (?)

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[github-actions]

Hi @kislaykishore, @raj-prince, @vipnydav, your feedback is needed to move this pull request forward. This automated reminder was triggered because there has been no activity for over 24 hours. Please provide your input when you have a moment. Thank you!

[github-actions]

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[github-actions]

Hi @kislaykishore, @vipnydav, @raj-prince, your feedback is needed to move this pull request forward. This automated reminder was triggered because there has been no activity for over 24 hours. Please provide your input when you have a moment. Thank you!

[github-actions]

Hi @kislaykishore, @vipnydav, @raj-prince, your feedback is needed to move this pull request forward. This automated reminder was triggered because there has been no activity for over 24 hours. Please provide your input when you have a moment. Thank you!

[github-actions]

Hi @kislaykishore, @vipnydav, @raj-prince, your feedback is needed to move this pull request forward. This automated reminder was triggered because there has been no activity for over 24 hours. Please provide your input when you have a moment. Thank you!