Tài liệu Avoiding Locking Scenarios docx

Avoiding Locking Scenarios = a Si wey ^ go, ss 8 & ok ORS S OR BOQ, 2 ¢ Best Practices — Agyiicavan AWG WGA LIN S = — Use least restrictive isolation level that maintains the data in

Avoiding Locking Scenarios

=

a Si wey ^ go, ss 8 & ok ORS S OR BOQ, 2

¢ Best Practices — Agyiicavan AWG WGA LIN S

=

— Use least restrictive isolation level that maintains the data integrity requirements of the application

— Reduce Isolation level of specific statements by using statement level isolation (i.e., WITH clause)

— CLOSE cursors WITH RELEASE to free locks prior to end of

transaction

— Perform updates as close to the end of the transaction as possible, to reduce exclusive lock duration

— COMMIT frequently to release locks

— Avoid multiple applications accessing the same tables, but acquiring locks in different orders (Access patterns should be similar)

— Avoid having multiple processes that access the same table for both reads and writes within the same transaction

Avoiding Locking Scenarios

Best Practices — Database

— Avoid lock escalations by increasing DB CFG parameters

LOCKLIST and/or MAXLOCKS

— Avoid lock timeouts:

« Adjust the DB CFG parameter LOCKTIMEOUT or use the SET

CURRENT LOCK TIMEOUT command

— Avoid deadlocks:

¢ Reduce row blocking during index and table scans:

— DB2_SKIPINSERTED to skip/ignore uncommitted inserted rows

— DB2_ SKIPDELETED to skip/ignore uncommitted deleted rows

— DB2 EVALUNCOMMITTED to defer locking until row is known to

satisfy query Uncommitted data will be evaluated Skips deleted rows

on table scans.

More Useful |

Locking

iegistry Variables for

¢ DB2 KEEPTABLELOCK

— allows DB2 to maintain the table lock when an

uncommitted read or cursor stability isolation level

is closed The table lock is released at the end of the transaction

- DB2 MAX NON TABLE LOCKS

— defines the maximum number of NON table locks

a transaction can have before it releases these locks Because transactions often access the

same table more than once, retaining locks and changing their state to NON can improve

performance

¢ DB2LOCK_TO_RB

— specifies whether lock timeouts cause the entire transaction to be rolled back, or only the current statement