Piye cara JVM memory lan garbage collection ngerjani?

Question

IT Interview Practice · Accepted Answer

JVM **manajeri memory kanthi otomatis** — nalokasiken objek lan mbebaskaken sing ora bisa diraih liwat **garbage collection (GC)** — supaya sampeyan ora perlu mbebaskaken memory kanthi manual. Ngerti babagan region memory lan kelakuwan GC penting banget kanggo ngrewangi performa lan diagnosa masalah memory. ## Region memory JVM ```text HEAP — where all OBJECTS live (shared across threads), GC operates here ├── Young Generation — new objects (most die young) │ ├── Eden — new allocations go here │ └── Survivor — objects that survived a young GC └── Old (Tenured) Gen — long-lived objects (promoted from young) STACK — per-thread; method frames, local variables, primitive locals, references Metaspace — class metadata (replaced PermGen in Java 8+) ``` Objek manggon ing **heap**; variabel lokal lan referensi manggon ing **stack** per thread. GC fokus ing heap. ## Hipotesis generasi ```text Observation: MOST objects die young (short-lived). → GC splits the heap into generations and collects the young gen FREQUENTLY (cheap, fast) and the old gen RARELY (expensive). ``` ## Piye GC ngerjani: mark lan sweep ```text 1. MARK — starting from GC roots (stack refs, static fields), mark all REACHABLE objects 2. SWEEP — reclaim memory of unmarked (unreachable) objects 3. COMPACT— (often) move survivors together to reduce fragmentation ``` Objek dadi garbage nalika ora **bisa diraih** saka GC root apa-apa. Sampeyan ora mbebaskaken — GC sing mangerteni lan mbukak. ## Minor GC versus Major GC ```text Minor GC — collects the Young Generation; frequent, fast, short pause Major/Full GC — collects the Old Generation (and more); rarer, longer pause → long Full GC pauses ("stop-the-world") are a common performance concern ``` ## Algoritma GC (pilih jajal workload) ```text G1 GC (default, Java 9+) — balanced, predictable pause times, good general choice Parallel GC — max throughput (batch jobs), longer pauses acceptable ZGC / Shenandoah — very low pause times for large heaps (latency-sensitive apps) ``` ## Memory leak isih kelakon (sanajan ana GC) ```java // ❌ a leak: a static collection that only grows keeps objects REACHABLE forever static List

Piye cara JVM memory lan garbage collection ngerjani?

Region memory JVM

Hipotesis generasi

Piye GC ngerjani: mark lan sweep

Minor GC versus Major GC

Algoritma GC (pilih jajal workload)

Memory leak isih kelakon (sanajan ana GC)

Piye dadi penting

Pitakon sing gegandhengan