Posts (238+)

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September 2026

Interpreter:Represent a Grammar and Evaluate It

Model a tiny promo DSL as AND/OR of percent-off and sku-in-category expressions that evaluate(Order), and skip it when a few ifs or a real parser would be honest.

Algorithms

Raft:Elect a Leader and Replicate a Log (Awareness, Not a From-Scratch Cluster)

Raft terms, leader election, and log replication at awareness depth — enough to know what etcd and Kafka-adjacent consensus are doing, not enough to ship your own cluster.

Design Patterns

Visitor:Add Operations Without Changing the Elements

Add CSV export and tax walks to a stable Sku / Category tree with accept(Visitor) so each new report is a class, not another method on every catalog type.

Algorithms

Rabin-Karp:Rolling Hash When You Need Many Pattern Checks

Slide a window hash in O(1), compare hashes first, then verify characters — the procedure for one needle or many needles against the same haystack.

Design Patterns

Prototype:Copy an Object Instead of Reconstructing It

Clone a configured DiscountPolicy, ChargeRequest, or gateway test double in Java instead of rebuilding constructor arguments — and skip clone() when new is cheaper or the copy shares mutable guts.

Algorithms

Two-Phase Commit:All Prepare, Then All Commit — and Why It Blocks

A coordinator asks every participant to prepare, then commit or abort together — and why a crashed coordinator leaves the cluster stuck.

Design Patterns

Memento:Snapshot State Without Breaking Encapsulation

Undo a checkout draft in Java by letting Order take an opaque snapshot — no public fields, no JSON dump, and no serializing OrderProcessor.

Design Patterns

Mediator:Keep Colleagues from Talking to Each Other

Stop DiscountPolicy, PaymentGateway, fraud, inventory, and the notifier from importing each other by letting CheckoutMediator own the checkout conversation.

Algorithms

Exponential Backoff:Retry With Jitter Instead of a Thundering Herd

Wait base × 2^attempt after a failure, cap the wait, and add jitter so retries do not stampede the same instant.

Design Patterns

Flyweight:Share What Does Not Change

Share immutable catalog SKU metadata across cart LineItems so a Black Friday order does not clone name, tax class, and image URL on every row.