LRU::Cache: Fast Perl LRU Cache in C

What if your Perl app’s biggest bottleneck — that endless churn of lookups and evictions — vanished into C-speed smoke?

LRU::Cache, the new CPAN module dropping like a mic in a quiet room, does exactly that. It’s a Least Recently Used cache rebuilt from the silicon up in XS, promising O(1) everything: gets, sets, peeks, deletes. No more Perl-level hacks masquerading as efficiency.

And here’s the kicker — in a world where Perl’s whispered about like yesterday’s news, this thing clocks 45 million set operations per second. Pure Perl? A measly 1.7 million. That’s not incremental; it’s a paradigm gut-punch.

How LRU::Cache Actually Works Under the Hood

Picture a doubly-linked list fused with a hash table. Keys map instantly to nodes; the list tracks recency. Touch an entry? Yank it from the middle, slap it at the head. Full? Chop the tail. Simple. Elegant. But in Perl?

Pure Perl versions tie hashes or juggle objects — dispatch overhead alone murders tight loops. LRU::Cache sidesteps all that. XS means C code slotted directly into the Perl interpreter. Every op zips through custom ops, no method resolution, no @_ unpacking. It’s like giving your cache a backstage pass to memory.

Every operation — get, set, delete, exists — is O(1). No Perl-level hash ties, no linked list objects, no method dispatch on the hot path if you don’t want it.

That’s straight from the module’s docs. And it delivers.

Take this snippet:

my $cache = LRU::Cache::new(3);
$cache->set('a', 1);
$cache->set('b', 2);
$cache->set('c', 3);
$cache->get('a');  # a to front: a->c->b
$cache->set('d', 4);  # evicts b

Dead simple. But peek() lets you snoop without promoting — gold for monitoring. oldest() and newest() hand back tail-head pairs. keys() spits MRU order. delete() returns the victim. It’s thoughtful.

Why Bother with Function-Style APIs in Perl?

Method calls in Perl? They’re toll roads. entersub op, resolution, shifting — it stacks up in loops. LRU::Cache’s import() unleashes lru_get(), lru_set(), etc. Compile-time magic swaps the call for a direct C jump via call checker. Pad-slurp the cache pointer. Boom — 2x method speeds, 5-20x pure Perl.

Benchmarks don’t lie. Single ops, no batches:

Those numbers? From real hardware, no smoke. Wrap your DNS resolver:

my $dns_cache = LRU::Cache::new(1000);
sub resolve {
    my ($domain) = @_;
    my $ip = lru_get($dns_cache, $domain);
    return $ip if defined $ip;
    $ip = expensive_dns_lookup($domain);
    lru_set($dns_cache, $domain, $ip);
    $ip;
}

Misses compute; hits scream from C. Evictions? Automatic housekeeping.

But wait — Perl in 2024? Who’s caching in Perl anymore? That’s my unique angle here: this isn’t just a module; it’s a flare for Perl’s performance underground. Remember Redis? Its LRU core in C made it a beast. Perl’s XS scene faded post-5.10, but LRU::Cache screams revival. Bold prediction: expect a wave of C/XS drops for hot-path libs. Perl’s garbage-collected efficiency + C bursts = sleeper hit for IoT edges, embedded, anywhere memory’s tight and loops burn.

Corporate hype? None here — it’s open-source, no VC spin. Just a dev tired of slow caches. Skeptical? cpanm LRU::Cache. Benchmark it yourself.

Is LRU::Cache Really 20x Faster Than Alternatives?

CHI? Tie::Cache? Solid, but Perl-heavy. CHI’s drivers vary; pure Perl LRU caps at millions ops/sec. XS::LRU exists, but older, less optimized. LRU::Cache’s custom ops edge it — function API crushes. Why? No Perl stack traces on every touch.

Architectural shift: Perl’s OP customization (pluggable ops) rarely flexed lately. This showcases it. Future-proof? Thread-safe? Docs say no shared mutability across threads — single-thread king. For moar? Fork per-worker.

Tradeoffs. Fixed size only — no LRU-K or adaptive. Values? Blobs, refs fine, but serialize big ones. Still, for keys-as-strings, values-as-anything? Perfect.

Real-world? Mojolicious sessions, DB query caches, API rate-limits. That DNS wrapper? Swap for Redis, sure — but Redis needs daemons, nets. Local LRU::Cache? Zero deps, microsecond hits.

Why Does LRU::Cache Matter for Perl Developers in 2024?

Perl’s not dead — it’s specialized. Bioinformatics, sysadmin scripts, legacy behemoths. Hot paths there beg C acceleration. This module lowers the XS barrier: OO interface + func speed. No more “pure Perl or bust.”

Historical parallel: 1990s Perl CGI boom rode fast regex engines. Now, caching. If Perl 7 lands with better XS interop, expect fireworks.

Critique time — why not Rust crate? Perl’s here, ecosystem intact. Porting? Pain. This fits now.

Install: cpanm LRU::Cache. XS needs compiler — standard for CPAN.

Short version: it’s fast. Stupid fast.

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Frequently Asked Questions

What is LRU::Cache in Perl?

LRU::Cache is a CPAN module implementing a fixed-size Least Recently Used cache in C via XS, with O(1) get/set/peek/delete ops up to 45M/sec.

How do I install and use LRU::Cache?

Run cpanm LRU::Cache. Then: my $cache = LRU::Cache::new(1000); $cache->set('key', $val); Or import funcs for max speed.

Is LRU::Cache faster than pure Perl caches?

Yes, 5-20x faster per benchmarks, thanks to custom C ops bypassing Perl dispatch overhead.