undo_management = manual
When creating a new database, Oracle will create a default system return segment in the System tablespace. The SYSTEM retreat should only be used to store the Rolling Record of Oracle System Transactions, and any user transaction should not be returned to the SYSTEM.
# After creating a database, you should create a non-SYSTEM return segment immediately in the System table space, because users need to create other tablespaces and return segments after the database is created. At this time, the rollback records of these operations will be saved in this non-System return segment without saving in the SYSTEM return. After the other tablespace and the retraction section are established, this non-SYSTEM back to the SYSTEM table space can be deleted.
The number of retire segments obtained at the time of the instance is determined by a variety of methods: • The number of public retort segments obtained by the instance is determined by the transaction, transaction_per_rollback_segments. The private rollback section and name acquired by the instance are determined by Rollback_SEGMENTS. # In addition, the maximum number of returned segments allowed by an instance MAX_ROLLBACK_SEGMENTS = CEIL (Transaction / Transaction_Per_Rollback_SEGMENTS).
In one example, if you use the public return segment and the private return segment, the instance first gets the private return segment specified by the ROLLBACK_SEGMENTS parameter, and then the value calculated by CEIL (Transactions / Transactions_Per_rollback_SEGments) and the acquired private rollback The difference between the number of segments needs to be compensated by obtaining a public retreat section. · Create a private return Create Rollback Segments XXXXTABLESPACE XXXSTORAGE (Initial XXX NEXT XXX OPTIMAL XXX PCTINCREASE 0 MINEXTENTS XXX MAXEXTENTS XXX) · Create a public return CREATE PUBLIC ROLLBACK Segments XXX ......
#online offline · ALTER ROLLBACK Segment XXX Online / Offline • Use the parameter file (private return to the private return) ROLLBACK_SEGMENTS to add a private return section into this parameter, then the status of the return segment will be permanently ONLNE After the retreat of the parameter file is restarted after the database is restarted, then restart again, it will become offline and the public return will not be restricted by the parameter file.
In the retreat section, the head of the segment stores the information on the retirement transaction being used. One transaction can only use a back to the back to store its rollback information, and a return segment can store multiple transactions back Retreat.
