MVCC (Multi-Version Concurrency Control) ni jinsi PostgreSQL inavyoshughulikia ufikiaji unaoendana — badala ya kufunga safu kwa usomaji, inaweka matoleo mengi ya safu, hivyo kila transaction inaona snapshot thabiti ya data. Faida kuu: wasomaji hawazuii waandishi, na waandishi hawazuii wasomaji, ikiwezesha concurrency ya juu.
Wazo la msingi: matoleo mengi ya safu
When a row is UPDATED, Postgres doesn't overwrite it — it creates a NEW version and
marks the old one obsolete. Different transactions can see different versions.
→ Each transaction sees a consistent SNAPSHOT of the database as of its start
(depending on isolation level), unaffected by others' uncommitted changes.
