golang-samber-hot
In-memory caching in Golang using samber/hot — eviction algorithms (LRU, LFU, TinyLFU, W-TinyLFU, S3FIFO, ARC, TwoQueue, SIEVE, FIFO), TTL, cache loaders, sharding, stale-while-revalidate, missing key caching, and Prometheus metrics. Apply when using or adopting samber/hot, when the codebase imports github.com/samber/hot, or when the project repeatedly loads the same medium-to-low cardinality resources at high frequency and needs to reduce latency or backend pressure.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-hot- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads golang-samber-hot automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Persona: You are a Go engineer who treats caching as a system design decision. You choose eviction algorithms based on measured access patterns, size caches from working-set data, and always plan for expiration, loader failures, and monitoring.
Using samber/hot for In-Memory Caching in Go
Generic, type-safe in-memory caching library for Go 1.22+ with 9 eviction algorithms, TTL, loader chains with singleflight deduplication, sharding, stale-while-revalidate, and Prometheus metrics.
Official Resources:
This skill is not exhaustive — refer to library documentation and code examples for more information:
- For Go package docs, symbols, versions, importers, and known vulnerabilities, → See
samber/cc-skills-golang@golang-pkg-go-devskill (godig), preferred over Context7 for Go package facts. - To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See
samber/cc-skills-golang@golang-goplsskill (gopls). - Context7 remains a fallback for docs not indexed on pkg.go.dev.
go get -u github.com/samber/hot
Algorithm Selection
Pick based on your access pattern — the wrong algorithm wastes memory or tanks hit rate.
| Algorithm | Constant | Best for | Avoid when |
|---|---|---|---|
| W-TinyLFU | hot.WTinyLFU | General-purpose, mixed workloads (default) | You need simplicity for debugging |
| LRU | hot.LRU | Recency-dominated (sessions, recent queries) | Frequency matters (scan pollution evicts hot items) |
| LFU | hot.LFU | Frequency-dominated (popular products, DNS) | Access patterns shift (stale popular items never evict) |
| TinyLFU | hot.TinyLFU | Read-heavy with frequency bias | Write-heavy (admission filter overhead) |
| S3FIFO | hot.S3FIFO | High throughput, scan-resistant | Small caches (<1000 items) |
| ARC | hot.ARC | Self-tuning, unknown patterns | Memory-constrained (2x tracking overhead) |
| TwoQueue | hot.TwoQueue | Mixed with hot/cold split | Tuning complexity is unacceptable |
| SIEVE | hot.SIEVE | Simple scan-resistant LRU alternative | Highly skewed access patterns |
| FIFO | hot.FIFO | Simple, predictable eviction order | Hit rate matters (no frequency/recency awareness) |
Decision shortcut: Start with hot.WTinyLFU. Switch only when profiling shows the miss rate is too high for your SLO.
For detailed algorithm comparison, benchmarks, and a decision tree, see Algorithm Guide.
Core Usage
Basic Cache with TTL
import "github.com/samber/hot"
cache := hot.NewHotCache[string, *User](hot.WTinyLFU, 10_000).
WithTTL(5 * time.Minute).
WithJanitor().
Build()
defer cache.StopJanitor()
cache.Set("user:123", user)
cache.SetWithTTL("session:abc", session, 30*time.Minute)
value, found, err := cache.Get("user:123")
Loader Pattern (Read-Through)
Loaders fetch missing keys automatically with singleflight deduplication — concurrent Get() calls for the same missing key share one loader invocation:
cache := hot.NewHotCache[int, *User](hot.WTinyLFU, 10_000).
WithTTL(5 * time.Minute).
WithLoaders(func(ids []int) (map[int]*User, error) {
return db.GetUsersByIDs(ctx, ids) // batch query
}).
WithJanitor().
Build()
defer cache.StopJanitor()
user, found, err := cache.Get(123) // triggers loader on miss
Capacity Sizing
Before setting the cache capacity, estimate how many items fit in the memory budget:
- Estimate single-item size — estimate size of the struct, add the size of heap-allocated fields (slices, maps, strings). Include the key size. A rough per-entry overhead of ~100 bytes covers internal bookkeeping (pointers, expiry timestamps, algorithm metadata).
- Ask the developer how much memory is dedicated to this cache in production (e.g., 256 MB, 1 GB). This depends on the service's total memory and what else shares the process.
- Compute capacity —
capacity = memoryBudget / estimatedItemSize. Round down to leave headroom.
Example: *User struct ~500 bytes + string key ~50 bytes + overhead ~100 bytes = ~650 bytes/entry
256 MB budget → 256_000_000 / 650 ≈ 393,000 items
If the item size is unknown, ask the developer to measure it with a unit test that allocates N items and checks runtime.ReadMemStats. Guessing capacity without measuring leads to OOM or wasted memory.
Common Mistakes
- Forgetting
WithJanitor()— without it, expired entries stay in memory until the algorithm evicts them. Always chain.WithJanitor()in the builder anddefer cache.StopJanitor(). - Calling
SetMissing()without missing cache config — panics at runtime. EnableWithMissingCache(algorithm, capacity)orWithMissingSharedCache()in the builder first. WithoutLocking()+WithJanitor()— mutually exclusive, panics.WithoutLocking()is only safe for single-goroutine access without background cleanup.- Oversized cache — a cache holding everything is a map with overhead. Size to your working set (typically 10-20% of total data). Monitor hit rate to validate.
- Ignoring loader errors —
Get()returns(zero, false, err)on loader failure. Always checkerr, not justfound.
Best Practices
- Always set TTL — unbounded caches serve stale data indefinitely because there is no signal to refresh
- Use
WithJitter(lambda, upperBound)to spread expirations — without jitter, items created together expire together, causing thundering herd on the loader - Monitor with
WithPrometheusMetrics(cacheName)— hit rate below 80% usually means the cache is undersized or the algorithm is wrong for the workload - Use
WithCopyOnRead(fn)/WithCopyOnWrite(fn)for mutable values — without copies, callers mutate cached objects and corrupt shared state
For advanced patterns (revalidation, sharding, missing cache, monitoring setup), see Production Patterns.
For the complete API surface, see API Reference.
If you encounter a bug or unexpected behavior in samber/hot, open an issue at https://github.com/samber/hot/issues.
Cross-References
- → See
samber/cc-skills-golang@golang-performanceskill for general caching strategy and when to use in-memory cache vs Redis vs CDN - → See
samber/cc-skills-golang@golang-observabilityskill for Prometheus metrics integration and monitoring - → See
samber/cc-skills-golang@golang-databaseskill for database query patterns that pair with cache loaders - → See
samber/cc-skills@promql-cliskill for querying Prometheus cache metrics via CLI
FAQ
What does the golang-samber-hot skill do?
In-memory caching in Golang using samber/hot — eviction algorithms (LRU, LFU, TinyLFU, W-TinyLFU, S3FIFO, ARC, TwoQueue, SIEVE, FIFO), TTL, cache loaders, sharding, stale-while-revalidate, missing key caching, and Prometheus metrics. Apply when using or adopting samber/hot, when the codebase imports github.com/samber/hot, or when the project repeatedly loads the same medium-to-low cardinality resources at high frequency and needs to reduce latency or backend pressure.
How do I install golang-samber-hot?
Run npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-hot in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/golang-samber-hot/ (personal) or .claude/skills/golang-samber-hot/ (project).
Which AI agents can use golang-samber-hot?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is golang-samber-hot safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains golang-samber-hot?
It is published by samber in samber/cc-skills-golang. It has 38,358 recorded installs.
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