1Z0-497 · Question #46
View the current parameter settings shown in the output below. NAMETYPEVALUE db_file_multiblock_read_count integer ddl_lock_timeout integer Distributed_lock_timeout integer dml_locks integer…
The correct answer is C. The second user's session waits for a time before producing a "resource busy" error. DB_FILE_MULTIBLOCK_READ_COUNT is one of the parameters you can use to minimize I/O during table scans. It specifies the maximum number of blocks read in one I/O operation during a sequential scan. The total number of I/Os needed to perform a full table scan depends on such…
Question
View the current parameter settings shown in the output below. NAMETYPEVALUE db_file_multiblock_read_count integer ddl_lock_timeout integer Distributed_lock_timeout integer dml_locks integer lock_sga boolean FALSE enab1e_dd1_1ogging boolean FALSE resumable_timeout integer A user logs in to the hrschema and issues the following commands:
SQL> CREATE TABLE emp (empno NUMBER(3), enamo VARCHAR2(20), sal NUMBER (8, 2)); SQL> INSERT INTO emp (empno, ename) VALUES(1, 'JAMES'); At this moment, a second user also logs in to the hrschema and issues the following command:
SQL> ALTER TABLE emp MODIFY salNUMBER(10, 2); What happens in this scenario?
Options
- AThe second user's session immediately produces a "resource busy" error.
- BThe second user's command executes successfully.
- CThe second user's session waits for a time before producing a "resource busy" error.
- DA deadlock is created.
How the community answered
(18 responses)- A6% (1)
- B11% (2)
- C83% (15)
Explanation
DB_FILE_MULTIBLOCK_READ_COUNT is one of the parameters you can use to minimize I/O during table scans. It specifies the maximum number of blocks read in one I/O operation during a sequential scan. The total number of I/Os needed to perform a full table scan depends on such factors as the size of the table, the multiblock read count, and whether parallel execution is being utilized for the operation. DDL_LOCK_TIMEOUT specifies a time limit for how long DDL statements will wait in a DML lock queue. The default value of zero indicates a status of NOWAIT. The maximum value of 1,000,000 seconds will result in the DDL statement waiting forever to acquire a DML lock. If a lock is not acquired before the timeout period expires, then an error is returned. DISTRIBUTED_LOCK_TIMEOUT specifies the amount of time (in seconds) for distributed transactions to wait for locked resources. A DML_LOCK is a lock obtained on a table that is undergoing a DML operation (insert, update, delete). DML_LOCKS specifies the maximum number of DML locks-one for each table modified in a transaction. The value should equal the grand total of locks on tables currently referenced by all users. For example, if three users are modifying data in one table, then three entries would be required. If three users are modifying data in two tables, then six entries would be required. LOCK_SGA locks the entire SGA into physical memory. It is usually advisable to lock the SGA into real (physical) memory, especially if the use of virtual memory would include storing some of the SGA using disk space. This parameter is ignored on platforms that do not support it. ENABLE_DDL_LOGGING enables or disables the writing of a subset of data definition language (DDL) statements to a DDL log. RESUMABLE_TIMEOUT enables or disables resumable statements and specifies resumable timeout at the system level.
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