Topic of Discussion : point out problems involved in space management when finer than page level granularity of locking and varying length records are to be supported efficiently.
The space released by a transaction during record deletion or update on a data page should not be consumed by another transaction, until the space releasing transaction is committed.
It is not desirable to do physical locking and logging of data within a page.
The logging and locking have to be logical within a page. eg (page #,slot #), where slot # identifies a location on the page which points to the actual location of the record, should be the record's lock name.
Garbage collection that collects unused space on a page should have to lock or log the record that are moved around within the page. This helps us in moving records within a page in a flexible manner.
Fig 9 shows that if the state of the page is not tracked properly, then redoing from an earlier point in the log leads to problems.
Typically each file has a few pages called FSIPS, also called SMPs. FSIP describes space information relating to many data or index pages.
FSIP keeps only approximate information and is consulted during updates (particularly inserts).
. Updates to FSIPs must be logged, which must be redo only changes and do logical undo with respect to the free space inventory updates
System must determine whether an operation causes the space information to change and if it does, then update FSIP and write the CLR describing the change.