I was looking through the notes and book and I'm not seeing a definition for "flush."  When in the notes it says "Flush the disk..." does that mean to delete everything on the disk?

My understanding is that we "flush the buffer" to the disk, meaning we write the data what data is currently in RAM to the corresponding hard disk memory locations, like saving a file. The significance of when we flush to disk is that it determines the state of our data after a crash. depending whether the transactions that were in progress got logged/committed/flushed

venny wrote:

Oh, my mistake I thought it said "flush the disk" whereas I've seen "flush the log."  Is this similar to "apply all the actions to the disk and clear out the log"  thus making the changes permanent? 

Log records like <START,T> and <UPDATE, T> are first written to a log buffer page in memory. Flush(log) simply writes all the log records in that buffer page to disk, and the buffer page can then be used for new log records.

venny wrote:

What is the difference between Flush() and commit?  If there is any.

They are two completely different things.

COMMIT is an SQL statement (like SELECT and UPDATE) and a db operation. COMMIT marks the end of a transaction, and if the commit operation is successful, the transaction is considered completed successfully with the ACID guarantees. Flush, as explained earlier, simply writes a memory buffer page to disk.