sql undo last query

First, back paragraph introduction In an Oracle database, when something modifies the data, Oracle first saves the original value of the data to a fallback segment. A thing can only save its fallback information to a fallback segment, while multiple

--Create the undo table spaceCreate undo Tablespace Undo_tbs DataFile ' size 500m;--Toggle the Undo table Spacealter system Set Undo_tablespace = Undo_tbs scope = both; Advice: About estimating the undo table Space >>>>>>>>>>>>>>>>>>> The script for

Oracle 10g and later versions have a new feature that automatically adjusts the undo retention time, which is much simpler to manage, for auto-scaling (Autoextend on) undo tablespace, Parameters Undo_ The retention is set as the lowest threshold for

The undo segment in the Undo table space is automatically generated, and Oracle automatically uses the undo segment of the Undo table space. As a high-level DBA, you need to understand how Oracle uses the Undo segment. This will solve the

In Oracle We do some updates, how Oracle's bottom layer is flowing, this article is to explain.     I. PrincipleSuppose we update a row of data in an OLTP system that has updated many fragmented records. So the actual steps for this update are as

Rollback segmentIt can be said that it is a disk storage area that provides consistent read and transaction integrity to maintain the image before data changes. When a transaction starts, it first writes the data before and after the change to the

The Oracle database uses undo to ensure consistent read and dirty read. User A updates the table and does not submit the table. User B queries the table, unsubmitted updates cannot appear in the user's query results. Instance simulation: the data in

No dirty reads occur. User A has updated the table and has not submitted the table. User B queries the table. unsubmitted updates cannot appear in the user's query results. Instance simulation: the data in the test table is as follows: 1. User a

MS SQL Server Query optimization methodThere are many reasons for the slow speed of queries, which are common1, no indexes, or no indexes (this is the most common problem with query slowness, is the flaw in programming)2, I/o throughput is small,

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