By Thomas Kyte, Darl Kuhn
Oracle Database Transactions and Locking printed presents much-needed info for construction scalable, high-concurrency purposes and install them opposed to the Oracle Database. learn this brief, 150-page publication that's tailored from professional Oracle Database structure to achieve an excellent and actual figuring out of the way locking and concurrency are handled by way of Oracle Database. additionally learn the way the Oracle Database structure contains consumer transactions, and the way you could write code to mesh with how Oracle Database is designed to function. reliable transaction layout is a crucial part of highly-concurrent purposes which are run by way of hundreds and hundreds, even hundreds of thousands of clients who're all executing transactions while. Transaction layout in flip depends a very good knowing of ways the underlying database platform manages of the locking of assets in an effort to hinder entry conflicts and information loss that would another way consequence from concurrent entry to info within the database.
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Extra info for Oracle Database Transactions and Locking Revealed
Example text
The RBS, SLOT, and SEQ values match the V$TRANSACTION information. This is my transaction ID. Now we’ll start another session using the same username, update some rows in EMP, and then try to update DEPT: EODA@ORA12CR1> update emp set ename = upper(ename); 14 rows updated. info Chapter 3 ■ Lock Types We’re now blocked in this session. username = USER; USERNAME SID RBS SLOT SEQ LMODE REQUEST --------------- ---------- ---------- ---------- ---------- ---------- ---------EODA 17 2 27 21201 0 6 EODA 22 2 27 21201 6 0 EODA 17 8 17 21403 6 0 EODA@ORA12CR1> select XIDUSN, XIDSLOT, XIDSQN from v$transaction; XIDUSN XIDSLOT XIDSQN ---------- ---------- ---------2 27 21201 8 17 21403 What we see here is that a new transaction has begun, with a transaction ID of (8,17,21403).
EODA@ORA12CR1> exec p PL/SQL procedure successfully completed. The procedure, P, will now show up in the DBA_DDL_LOCKS view. We have a parse lock on it: EODA@ORA12CR1> select session_id sid, owner, name, type, 2 mode_held held, mode_requested request 3 from dba_ddl_locks 4 where session_id = (select sid from v$mystat where rownum=1) 5 / SID OWNER NAME TYPE HELD REQUEST ------ -------- --------------------- -------------------- ---------- -------22 EODA P Table/Procedure/Type Null None ... 22 SYS DATABASE 18 Null None 9 rows selected.
If argument A is not null, then it returns argument B; otherwise, it returns argument C. This query assumes that the owner of the constraint is the owner of the table and index as well. If another user indexed the table or the table is in another schema (both rare events), it will not work correctly. info Chapter 2 ■ Locking and Issues The prior script also checks to see if the index type is a B*Tree index (NORMAL or NORMAL/REV). We’re checking to see if it’s a B*Tree index because a bitmap index on a foreign key column does not prevent the locking issue.