Transaction Recovery

enrique_aeo
enrique_aeo used Ask the Experts™
on
hi experts, i am reading about Transaction Recovery
but i do not understand thisn concepts
Roll forward
Roll back
Checkpoint

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Billing Engineer
Most Valuable Expert 2014
Top Expert 2009
Commented:
when you create a transaction, the change is written FIRST in the transaction log file, to disk, and in parallel in the memory blocks.when you commit, that fact is also written in the transaction log file, but it changes nothing to the data or the date files.on checkpoint, the dirty buffers (which are the data pages in memory) are flushed (written) to disk, which is independant of the commit.of between the commit and the checkpoint the system crashes, on restart, sql server will be able to roll forward the transaction by reading the transaction log file.if there was no commit, after system crash, sql server will roll backwards and blocks in the data files that had already been updated by the checkpoint, but not committed.hope this clarifies

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