Yaya yadda ajiya JVM da tara gida ke aiki?

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JVM **ta sarrafa ajiya ta kanta** — ta ba da jiyya kuma ta 'yantar da waɗanda ba za a iya samun ta — ta hanyar **tara gida (GC)** — don haka ba buƙatar ka saki ajiya ta kankanta. Fahimtar yankunan ajiya da halayen GC sune mabuɗi don dandali aiki da gida matsaloli. ## Yankunan ajiya 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+) ``` Abjejin suna zaune a kan **jaji**; mahimman jiyya da kuma sanannun jiya suna zaune a kan **kafofin aiki** na kowane zaren. GC yana da ziyarci kan jaji. ## Tunanin bayar da haihuwa ```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). ``` ## Yaya GC ke aiki: alama da share ```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 ``` Abjekta itace gida ne lokacin da ba a iya **samun ta** daga GC tushe. Ba ka saki ita — GC ne ke cewa kuma ya dawo da ita. ## Little vs babbar 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 ``` ## Algorithms GC (zaɓi bisa aiki) ```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) ``` ## Buɗewar ajiya har yanzu ina (duk da GC) ```java // ❌ a leak: a static collection that only grows keeps objects REACHABLE forever static List