1.

Explain One to One (1:1), One to Many (1:N) and Man to Many (N:N) mapping with an example?

Answer»

Write-ahead transaction log controls & DEFINED recording of DATA modifications to disk. To maintain ACID (Atomicity, Consistency, Isolation, and Durability) property of DBMS, SQL Server uses a write-ahead log (WAL), which guarantees that no data modifications are written to disk before the associated log record is written to disk.

Write-ahead log WORK as below:-

  • SQL Server maintains a buffer cache to maintain data pages on retrieval
  • When a page is modified in the buffer cache, it marked as dirty. The page is not immediately written back to disk.
  • A data page can be modified multiple times before written to disk but maintain separate log ENTRY a transaction log record.
  • The log records must be written to disk before the associated dirty page is REMOVED from the buffer cache and written to disk.


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