Database/Oracle (118) 썸네일형 리스트형 103 - [Oracle 19C] About the Undo Retention Period Managing UNDO Data About the Undo Retention Period UNDO_RETENTION The default is 900s Which is 15m The user A should see the data as 10:00 exactly And this is called read consistency User B - This will not reflect the user A query, User A still see the old data, because he execute the query at 10:00 am 102 - [Oracle 19C] Overview of Automatic Undo Management Managing UNDO Data Overview of Automatic Undo Management Oracle provides a fully automated mechanism for managing undo information and space. the database manages undo segments in an undo tablespace Automatic undo management is the default mode for a newly installed database. An auto extending undo tablespace named UNDOTBS1 is automatically created when you create the database with Databas.. 101 - [Oracle 19C] Local Undo Mode vs Shared Undo Mode Managing UNDO Data Local Undo Mode Versus Shared Undo Mode "LOCAL_UNDO_ENABLED= true" - This mean each pluggable can have its own undo There is only one shared UNDO tablespace(in CDB root). There can be a local UNDO tablespacein each PDB You can set a CDB in local UNDO mode either at CDB creation or by altering the CDB property. table :DATABASE_PROPERTIESproperty LOCAL_UNDO_ENABLED= true note.. 100 - [Oracle 19C] Comparing Undo Data and Redo Data Managing UNDO Data Comparing Undo Data and Redo Data Redo log files stores changes to the database as they occur and are used for data recovery. UNDO Redo Used for Rollback, read consistency, flashback Rolling forward of database changes Stored in Undo segments Redo Log Files Example show user; show CON_NAME; /* USER is "PDB10_ADMIN" CON_NAME ------------------------------ PDB10 */ select TABLES.. 99 - [Oracle 19C] Managing UNDO Data Managing UNDO Data EMP table empid sal 100 5000 UPDATE EMP SET SAL=6000 where empid=100; • The Oracle Database server saves the old value (undo data) when a process changes data in a database. • It stores the data as it exists before modifications. • Retained at least until the transaction is ended. UNDO Data used to support : Rollback operations Read-consistent queries Oracle Flashback Query, O.. 98 - [Oracle 19C] Managing Resumable Space Allocation Managing Resumable Space Allocation Managing Resumable Space Allocation A resumable statement: 1- Enables you to suspend large operations instead of receiving an error 2- Gives you a chance to fix the problem while the operation is suspended, rather than starting over 3-Is suspended for the following conditions: >>Out of space >>Maximum extents reached >>Space quota exceeded 4-Can be suspended a.. 97 - [Oracle 19C] Segment Advisor & Example Managing Storage Space - Segment Advisor Managing Storage Space Segment Advisor • We use the Segment Advisor to identify segments that would benefit from online segment shrink. • Only segments in locally managed tablespaces with automatic segment space management (ASSM) are eligible. • Segment Advisor can be automatic or manual. • Running the Segment Advisor Manually with PL/SQL using package DB.. 96 - [Oracle 19C] Reclaiming Wasted Space Managing Storage Space - Reclaiming Wasted Space Managing Storage Space Reclaiming Wasted Space Over time, updates and deletes on objects within a tablespace can create pockets of empty space that individually are not large enough to be reused for new data. This type of empty space is referred to as fragmented free space. Objects with fragmented free space can result in much wasted space, and ca.. 이전 1 2 3 4 5 6 ··· 15 다음
