Transaction Log Notes

442; transaction logs. Critical info we need to be aware of this is what deals with disaster recovery all through log and audit files. Back up and recovery is one of the 9 functions. Log files is what allows dbms to perform the recovery.

Lost updates and uncommitted data; never know when db will crash. What happens to info that crashed before making to db? Understand diff strategies for dealing with these kind of disasters and how much recovery is made. This functionality is what you pay for. See whats not happening for open source free stuff bc its not available in those. Understand concept of COMMIT. “Burn it in”

Multiuser level access; s447; scheduler; utility that determines who goes next. “Traffic cop”

449-issue of locking. Multiple types of locks. Different locking strategies-optimistic/pessimistic. Db level, table lock, row, page->level locks.

When we talk about pages, we’re talking about memory. Page will never be big enough to hold entire db. So a page worth will be swapped. Once page size is, then table size. DBA optimizes size of page with table. Row is individual instance of attribute. Thrashing-NEED to know. Calculate Thrash rate. DBA optimize to reduce thrashing rate. Thrashing swapping in and out to get info.

452; Locking, two phase locking, then deadlocks(db crashes down)

Concurrency control with time stamping

Wait & die/ wounded wait schemes

Transaction recovery; how do we clean things up. Last thing we want to do is lose data and have it recreated. Store everything and try to fix itself.