Questions?
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Transaction Table: TT
Dirty Page Table: DPT

Log Entries
===============================

LSN: Log sequence number


LSN  Ti updates Pi  old_value  new_value PREV_LSN
LSN  Ti commit PREV_LSN
LSN  Ti abort  PREV_LSN
LSN  Ti end  PREV_LSN

LSN  undo (Ti updates Pi old_value  new_value)



Checkpoints

LSN BEGIN CHECKPOINT
LSN dump of TT
LSN dump of DPT
LSN END CHECKPOINT 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

FORCE/STEAL


FORCE:

Whenever a transaction Ti wants to commit:

   1. flush the log to disk

   2. Write all the pages modified by Ti

   3. Write commit record for Ti to log, flush the log to disk

   4. Allow Ti to commit



NO FORCE:

Whenever a transaction Ti wants to commit:

   1. Write the commit record for Ti and flush the log to disk

   2. Allow Ti to commit



(*) Pages modified by the transaction will be written to disk by the
    DBMS as needed/not needed by other transactions



If FORCE is used -> Recovery does not need REDO operations.







~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

STEAL:

Whenever a transaction wants to use a memory block allocated to a
page modified by an uncommited transaction:

    1. Flush the log (Write Ahead Logging)

    2. Write the modified page to disk and free up memory
    it occupied




NO STEAL:

Pin all memory blocks occupied by an uncommitted transaction
and keep all dirty pages in memory until transaction commits.


If no steal is used, then recovery does not need to use UNDO steps.