Step-by-Step Internal Flow

1. BEGIN → The database assigns a transaction ID (TID) and starts tracking all operations.

2. Read/Write Operations → Data pages are fetched from disk into the Buffer Pool.

3. Locking / MVCC →

   • Lock-based systems: lock rows/tables to ensure isolation.

   • MVCC systems: keep multiple versions of data so reads don’t block writes.

4. Undo Logging → Before any change, the old value is written to an Undo Log.

5. Change in Memory → Updates are made to in-memory pages in the buffer pool.

6. Redo Logging (WAL) → The intended changes are written to a Write-Ahead Log on disk.

7. Commit → The WAL is flushed to disk, guaranteeing durability.

8. Post-Commit → Locks are released, and dirty pages are eventually written to disk.

9. Rollback (if needed) → Use the Undo Log to restore old values.

Read More: https://jating4you.blogspot.com/2025/08/understanding-internal-working-of.html