Chapter 21: Locking Commands and Options

Session-level transaction isolation levels and readpast

For data-only-locked tables, the effects of readpast on a table in a select command are shown in Table 21-1.

**Table 21-1: Session-level isolation level and the use of readpast**
Session Isolation Level	Effects
0, read uncommitted (dirty reads)	readpast is ignored, and rows containing uncommitted transactions are returned to the user. A warning message is printed.
1, read committed	Rows or pages with incompatible locks are skipped; no locks are held on the rows or pages read.
2, repeatable read	Rows or pages with incompatible locks skipped; shared locks are held on all rows or pages that are read until the end of the statement or transaction.
3, serializable	readpast is ignored, and the command executes at level 3. The command blocks on any rows or pages with incompatible locks.