Cursor Isolation

Notes

• A consistent read is done using a snapshot.
• A current read is done using the latest committed version of a row and latest means right now, not the snapshot from statement start.
• A locking read is done as part of the WHERE clause processing for INSERT ... SELECT, UPDATE, DELETE and SELECT ... FOR UPDATE statements.

Features

• Read committed and repeatable read will be provided.
• Read committed and repeatable read provide consistent read for SELECT statements via a snapshot per statement for read committed and snapshot per transaction for repeatable read.
• TODO -- determine whether locking reads use consistent or current reads.
• Rows matched for locking-reads are locked until commit or rollback. TODO - determine whether early unlock can be done for rows when the row does not match non-index predicates.

Background