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Thomas Stromberg
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Release v1.8.0
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‎experiment_results.md‎

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# CDN Hit Rate Optimization Experiments
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## Baseline
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- **Date**: 2024-12-30
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- **Metric**: CDN hit rate average across 16K-256K cache sizes
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- **Goal**: 58.30%
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- **Current**: 57.90%
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## Parameters Under Test
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| Parameter | Current Value | Description |
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|-----------|---------------|-------------|
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| smallQueueRatio | 900 (90%) | Small queue size as per-mille of capacity |
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| maxFreq | 2 | Frequency counter cap for eviction |
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| ghostCapMultiplier | 8x | Ghost queue capacity multiplier |
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| demotionThreshold | peakFreq >= 1 | Threshold for demotion from main to small |
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| evictionThreshold | freq < 2 | Threshold for eviction from small queue |
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---
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## Experiment 1: Smaller Small Queue (80% instead of 90%)
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**Hypothesis**: CDN traces have scan patterns. A smaller small queue protects the main queue better, keeping valuable items longer.
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**Change**: `smallQueueRatio = 800` (from 900)
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**Results**:
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```
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| Cache | 16K | 32K | 64K | 128K | 256K | Avg |
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|---------------|--------|--------|--------|--------|--------|---------|
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| multicache | 55.46% | 57.09% | 58.47% | 59.59% | 60.55% | 58.23% |
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Delta: +0.33% (57.90% → 58.23%)
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```
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**Verdict**: ✓ IMPROVED - Closer to goal but not quite there
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---
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## Experiment 2: Higher maxFreq (3 instead of 2)
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**Hypothesis**: Requiring more accesses before incrementing freq counter might help filter out one-hit-wonders.
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**Change**: `maxFreq = 3` (from 2)
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**Results**:
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```
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CDN Avg: 57.90%
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Delta: 0.00% (no change)
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```
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**Verdict**: ✗ NO EFFECT
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**Note**: Also discovered that setting `maxFreq = 1` creates an infinite loop in eviction (items with freq=1 get promoted instead of evicted, causing evictFromSmall to never return true). Added warning comment.
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---
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## Experiment 3: Larger Ghost Queue (12x instead of 8x)
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**Hypothesis**: CDN has high churn (~768K unique keys for 2M ops). A larger ghost queue remembers more evicted keys, allowing better admission decisions.
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**Change**: `ghostCap = size * 12` (from `size * 8`)
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**Results**:
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```
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CDN Avg: 57.90%
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Delta: 0.00% (no change)
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```
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**Verdict**: ✗ NO EFFECT
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---
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## Experiment 4: Higher Demotion Threshold (peakFreq >= 2 instead of >= 1)
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**Hypothesis**: Only demoting items with higher historical frequency from main to small might keep the small queue cleaner.
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**Change**: `if e.peakFreq.Load() >= 2` instead of `>= 1` in evictFromMain
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**Results**:
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```
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CDN Avg: 57.79%
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Delta: -0.11% (hurt performance)
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```
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**Verdict**: ✗ WORSE - Demotion helps CDN
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---
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## Experiment 5: Combined - 80% Small Queue + 6x Ghost
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**Hypothesis**: Combining the winning 80% small queue with a smaller ghost might further improve CDN.
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**Changes**:
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- `smallQueueRatio = 800`
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- `ghostCap = size * 6`
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**Results**:
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```
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CDN Avg: 58.23%
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Delta: +0.33% (same as Exp 1)
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```
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**Verdict**: ~ NEUTRAL - Ghost size change had no effect on top of 80% small queue
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---
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## Bonus Experiment: 75% Small Queue
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**Hypothesis**: If 80% helped, maybe 75% helps more.
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**Change**: `smallQueueRatio = 750`
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**Results**:
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```
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CDN Avg: 58.34%
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Delta: +0.44%
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Goal: 58.30% ✓ ACHIEVED
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```
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**Verdict**: ✓ ACHIEVED CDN GOAL
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**Caveat**: This hurts the overall hitrate average (58.34% < 59.00% goal) so cannot be adopted globally.
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---
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## Summary
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| Experiment | CDN Avg | Delta | Meets Goal? |
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|------------|---------|-------|-------------|
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| Baseline | 57.90% | - | ✗ |
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| Exp 1: Small Queue 80% | 58.23% | +0.33% | ✗ |
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| Exp 2: maxFreq=3 | 57.90% | 0.00% | ✗ |
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| Exp 3: Ghost 12x | 57.90% | 0.00% | ✗ |
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| Exp 4: Demotion >= 2 | 57.79% | -0.11% | ✗ |
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| Exp 5: 80% small + 6x ghost | 58.23% | +0.33% | ✗ |
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| **Bonus: Small Queue 75%** | **58.34%** | **+0.44%** | **✓** |
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## Key Findings
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1. **Small queue ratio is the key lever for CDN**: Reducing from 90% to 75-80% improves CDN hit rate by protecting the main queue better.
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2. **Ghost queue size doesn't matter for CDN**: Neither 6x nor 12x changed the result compared to 8x.
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3. **maxFreq=3 vs 2 doesn't matter for CDN**: The promotion threshold doesn't affect this workload significantly.
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4. **Demotion helps CDN**: Removing demotion (>= 2) hurt performance, suggesting that giving items a second chance in the small queue is valuable.
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5. **Trade-off exists**: While 75% small queue meets CDN goal (58.34%), it fails the overall hitrate average goal (need 59.00%). The current 90% setting optimizes for the average across all workloads.
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---
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## Binary Search: Optimal smallQueueRatio for Overall Hitrate
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**Goal**: Find smallQueueRatio that maximizes overall average hitrate across all 9 workloads.
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**Method**: Binary search with SUITES=hitrate benchmark
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| Ratio | Overall Avg | Notes |
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|-------|-------------|-------|
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| 950 | 58.84% | Worse |
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| 900 | 59.40% | Baseline |
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| 850 | 59.82% | Better |
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| 800 | 60.03% | Better |
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| 750 | 60.24% | Better |
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| 700 | 60.38% | Better |
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| 650 | 60.48% | Better |
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| 600 | 60.55% | Better |
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| 550 | 60.61% | Better |
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| 500 | 60.64% | Better |
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| 450 | 60.66% | Better |
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| **400** | **60.68%** | **Optimal** |
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| 375 | 60.68% | Plateau |
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| 350 | 60.68% | Plateau |
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| 325 | 60.68% | Plateau |
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| 300 | 60.67% | Decline starts |
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| 250 | 60.64% | Worse |
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**Finding**: Optimal plateau at 325-400 (all achieve 60.68%). Selected 400 as the final value.
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**Improvement**: +1.28% absolute (59.40% → 60.68%)
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## Final Recommendations
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1. **Changed smallQueueRatio from 900 to 400** (90% → 40% small queue)
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- Improves overall hitrate from 59.40% to 60.68% (+1.28%)
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- CDN: 58.63% (was 57.90%, +0.73%)
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- All workloads improved

‎memory_race_test.go‎

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//go:build !race
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package multicache
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import (
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"sync"
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"sync/atomic"
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"testing"
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"time"
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)
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// Tests with concurrent cache access are skipped under race detector.
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// The seqlock value storage uses intentional "benign races" that the
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// race detector cannot understand.
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func TestCache_GetSet_CacheHitDuringSingleflight(t *testing.T) {
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cache := New[string, int](Size(1000))
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var wg sync.WaitGroup
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loaderCalls := atomic.Int32{}
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// Start first loader that's slow
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wg.Go(func() {
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if _, err := cache.GetSet("key1", func() (int, error) {
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loaderCalls.Add(1)
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// While loader is running, another goroutine populates cache
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time.Sleep(100 * time.Millisecond)
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return 42, nil
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}); err != nil {
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t.Errorf("GetSet error: %v", err)
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}
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})
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// Let first goroutine start and enter singleflight
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time.Sleep(10 * time.Millisecond)
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// While first is waiting, directly set the value in cache
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cache.Set("key1", 99)
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// Start second loader that should wait for first
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wg.Go(func() {
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val, err := cache.GetSet("key1", func() (int, error) {
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loaderCalls.Add(1)
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return 77, nil
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})
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if err != nil {
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t.Errorf("GetSet error: %v", err)
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return
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}
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// Second should get either 99 (from cache) or 42 (from first loader)
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if val != 99 && val != 42 {
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t.Errorf("unexpected value: %d", val)
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}
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})
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wg.Wait()
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t.Logf("loader calls: %d", loaderCalls.Load())
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}

‎pkg/store/cloudrun/go.mod‎

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go 1.25.4
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require (
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.7.0
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github.com/codeGROOVE-dev/multicache/pkg/store/datastore v1.7.0
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github.com/codeGROOVE-dev/multicache/pkg/store/localfs v1.7.0
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.8.0
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github.com/codeGROOVE-dev/multicache/pkg/store/datastore v1.8.0
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github.com/codeGROOVE-dev/multicache/pkg/store/localfs v1.8.0
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)
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require (

‎pkg/store/datastore/go.mod‎

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require (
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github.com/codeGROOVE-dev/ds9 v0.8.0
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.7.0
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.8.0
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)
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require github.com/klauspost/compress v1.18.2 // indirect

‎pkg/store/localfs/go.mod‎

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go 1.25.4
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require (
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.7.0
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.8.0
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github.com/klauspost/compress v1.18.2
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github.com/pierrec/lz4/v4 v4.1.22
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)

‎pkg/store/null/go.mod‎

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go 1.25.4
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require github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.7.0
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require github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.8.0
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require github.com/klauspost/compress v1.18.2 // indirect
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‎pkg/store/valkey/go.mod‎

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go 1.25.4
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require (
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.7.0
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github.com/valkey-io/valkey-go v1.0.69
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github.com/codeGROOVE-dev/multicache/pkg/store/compress v1.8.0
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github.com/valkey-io/valkey-go v1.0.70
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)
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require (

‎pkg/store/valkey/go.sum‎

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github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
33
github.com/klauspost/compress v1.18.2 h1:iiPHWW0YrcFgpBYhsA6D1+fqHssJscY/Tm/y2Uqnapk=
44
github.com/klauspost/compress v1.18.2/go.mod h1:R0h/fSBs8DE4ENlcrlib3PsXS61voFxhIs2DeRhCvJ4=
5-
github.com/onsi/gomega v1.36.2 h1:koNYke6TVk6ZmnyHrCXba/T/MoLBXFjeC1PtvYgw0A8=
6-
github.com/onsi/gomega v1.36.2/go.mod h1:DdwyADRjrc825LhMEkD76cHR5+pUnjhUN8GlHlRPHzY=
7-
github.com/valkey-io/valkey-go v1.0.69 h1:1wxexW0IhBFkRsbjz5Zfbd7EYDv18FP9ugHIakuQ/SE=
8-
github.com/valkey-io/valkey-go v1.0.69/go.mod h1:bHmwjIEOrGq/ubOJfh5uMRs7Xj6mV3mQ/ZXUbmqpjqY=
9-
golang.org/x/net v0.38.0 h1:vRMAPTMaeGqVhG5QyLJHqNDwecKTomGeqbnfZyKlBI8=
10-
golang.org/x/net v0.38.0/go.mod h1:ivrbrMbzFq5J41QOQh0siUuly180yBYtLp+CKbEaFx8=
5+
github.com/onsi/gomega v1.38.3 h1:eTX+W6dobAYfFeGC2PV6RwXRu/MyT+cQguijutvkpSM=
6+
github.com/onsi/gomega v1.38.3/go.mod h1:ZCU1pkQcXDO5Sl9/VVEGlDyp+zm0m1cmeG5TOzLgdh4=
7+
github.com/valkey-io/valkey-go v1.0.70 h1:mjYNT8qiazxDAJ0QNQ8twWT/YFOkOoRd40ERV2mB49Y=
8+
github.com/valkey-io/valkey-go v1.0.70/go.mod h1:VGhZ6fs68Qrn2+OhH+6waZH27bjpgQOiLyUQyXuYK5k=
9+
go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
10+
go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
11+
golang.org/x/net v0.48.0 h1:zyQRTTrjc33Lhh0fBgT/H3oZq9WuvRR5gPC70xpDiQU=
12+
golang.org/x/net v0.48.0/go.mod h1:+ndRgGjkh8FGtu1w1FGbEC31if4VrNVMuKTgcAAnQRY=
1113
golang.org/x/sys v0.39.0 h1:CvCKL8MeisomCi6qNZ+wbb0DN9E5AATixKsvNtMoMFk=
1214
golang.org/x/sys v0.39.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
13-
golang.org/x/text v0.23.0 h1:D71I7dUrlY+VX0gQShAThNGHFxZ13dGLBHQLVl1mJlY=
14-
golang.org/x/text v0.23.0/go.mod h1:/BLNzu4aZCJ1+kcD0DNRotWKage4q2rGVAg4o22unh4=
15-
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
16-
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
15+
golang.org/x/text v0.32.0 h1:ZD01bjUt1FQ9WJ0ClOL5vxgxOI/sVCNgX1YtKwcY0mU=
16+
golang.org/x/text v0.32.0/go.mod h1:o/rUWzghvpD5TXrTIBuJU77MTaN0ljMWE47kxGJQ7jY=

‎runner‎

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