Kif jaħdem il-memorja tal-JVM u l-garbage collection?

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Il-JVM **jimmaniġġja l-memorja awtomatikament** — taqassam oġġetti u taħlif dawk li ma jistgħux jingħaddu permezz tal-**garbage collection (GC)** — sabiex m'għandekx bżonn taħlif il-memorja manwalment. L-għarfien tal-meridjani tal-memorja u l-imġiba tal-GC huwa essenzjali għat-tweaking tal-prestazzjoni u d-dijanjosi tal-problemi tal-memorja. ## Reġjuni tal-memorja tal-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+) ``` Oġġetti jgħixu fuq il-**heap**; il-varjabbli lokali u r-referenzi jgħixu fuq il-**stacks** għal kull thread. GC jiffoka fuq il-heap. ## L-ipoteżi ġenerazzjonali ```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). ``` ## Kif jaħdem GC: immark u isweep ```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 ``` Oġġett huwa garbage meta m'għadux **jingħadd** minn ebda root tal-GC. Int m'għandekx taħlifu — il-GC isibu u jirrevendika. ## Minor GC vs 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 ``` ## Algoritmi GC (għażel skond il-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) ``` ## Il-memory leaks għad iseħħu (minkejja GC) ```java // ❌ a leak: a static collection that only grows keeps objects REACHABLE forever static List

Reġjuni tal-memorja tal-JVM

L-ipoteżi ġenerazzjonali

Kif jaħdem GC: immark u isweep

Minor GC vs Major GC

Algoritmi GC (għażel skond il-workload)

Il-memory leaks għad iseħħu (minkejja GC)

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