Oracle 01555了解错误代码，有效解决方案（oracle 01555）

Oracle 01555: Understanding the Error Code and Effective Solutions

Oracle 01555 is an error code that often appears during a database query. It indicates that a transaction has been rolled back to a previous state due to a lack of undo space. This error can occur in several scenarios, such as when a query involves a large amount of data or when the database is running out of space.

Understanding the Error Code:

When an Oracle database processes a user query, it uses a technique called snapshot too old (STO) to ensure the transaction’s data integrity. The STO technique essentially means that Oracle snapshots the database state at the beginning of a transaction and uses it to ensure that the data being queried is consistent throughout the transaction’s execution.

However, if a transaction runs for too long or the undo tablespace does not have enough space to record changes, Oracle will not be able to mntn the consistency of the transaction. As a result, the transaction will fl, and the Oracle 01555 error code will appear.

Effective Solutions:

There are several effective solutions to the Oracle 01555 error code. Here are some of them:

1. Increase Undo Tablespace:

One of the most common causes of the Oracle 01555 error is a lack of undo space. This can be addressed by increasing the undo tablespace. To do this, you can execute the following SQL command:

ALTER TABLESPACE undo_tablespace_name ADD DATAFILE ‘/path/to/new/file.dbf’ SIZE [size in MB];

2. Optimize Query:

Another way to address the Oracle 01555 error is to optimize the query. This can be done by re-writing the query to use less data or by indexing the tables used in the query. You can use the Oracle optimizer to help you find the best query execution plan. Here is an example of how to use the Oracle optimizer:

SELECT /*+ gather_plan_statistics */ * FROM table_name WHERE column_name = ‘value’;

SET AUTOTRACE TRACE;

3. Increase UNDO_RETENTION:

Increasing the UNDO_RETENTION parameter can also help prevent the Oracle 01555 error. This parameter determines how long Oracle keeps undo data before purging it. Increasing the value of this parameter will allow Oracle to mntn the consistency of transactions that run for longer periods. Here is an example of how to increase UNDO_RETENTION:

ALTER SYSTEM SET UNDO_RETENTION = number_of_seconds;

4. Use Flashback Queries:

Flashback queries can help you recover lost data due to the Oracle 01555 error. These queries use the undo data to restore a previous state of the database. Here is an example of how to use flashback queries:

SELECT * FROM table_name AS OF TIMESTAMP SYSDATE – 1/24;

Conclusion:

The Oracle 01555 error code can be frustrating to deal with, especially if you are working with a large database. However, by understanding the error code and following these effective solutions, you can prevent it from happening and ensure the data integrity of your transaction.