Oracle Server Manager User's Guide

The Rollback Monitor

The Rollback Monitor displays statistics and information about online rollback segments. The following figure illustrates the left-most columns of the Rollback Monitor.

Figure 11 - 9. Rollback Monitor

The Rollback Monitor is described below:

RS ID Name of the rollback segment.
Rollback Segment Rollback segment number.
Size (bytes) Size of the rollback segment, in bytes.
Extents Number of extents in the rollback segment.
Active Xactions Number of active transactions using the rollback segment.
Write Rate (bytes/s) Rate at which bytes were written to the rollback segment since the last sample.
Header Gets Number of times the rollback segment's header was accessed since the last sample.
Header Waits Number of times a process had to wait to access the rollback segment's header since the last sample.
Optimal Size Optimal size of the rollback segment.
HWM Size High water mark for the rollback segment (the largest size the rollback segment has grown to), in bytes.
Average Active Current average size of active extents (extents that contain uncommitted transaction data), in bytes.
Average Shrink Total size of freed extents divided by number of shrinks, in bytes.
Wraps Number of times the rollback segment wraps from one extent to another.
Extends Number of times the rollback segment was extended and allocated a new extent.
Shrinks Number of times the rollback segment shrank, deallocating one or more extents.

Attention: In the Rollback Monitor you can sort on the RS ID, Rollback Segment, Size, Extents, Active Xactions, Optimal Size, HWM Size, Average Active, Average Shrink, Wraps, Extends, and Shrinks columns.

Filters

The following filter is available in the Rollback Monitor:

Rollback Segment Name Filter for the rollback segment name. Monitor displays information only for rollback segments whose names match the Rollback Segment Name filter.

SQL Worksheet Equivalent

To start the Rollback Monitor from a SQL Worksheet, you can use the following Server Manager command:

	MONITOR ROLLBACK

Required Views

To use the Rollback Monitor, you must have access to:

V$ROLLNAME

V$ROLLSTAT

Interpreting Rollback Statistics

When you have multiple rollback segments, the values in the Header Gets column should be roughly equal for all rollback segments. This indicates that the rollback segments are being accessed evenly.

If the value in the Extents column is high, you may want to create additional rollback segments or increase the size of current segments.

A high value in the Header Waits column indicates contention for the headers of rollback segments. In this case, you should consider adding more rollback segments.

RS ID	Name of the rollback segment.
Rollback Segment	Rollback segment number.
Size (bytes)	Size of the rollback segment, in bytes.
Extents	Number of extents in the rollback segment.
Active Xactions	Number of active transactions using the rollback segment.
Write Rate (bytes/s)	Rate at which bytes were written to the rollback segment since the last sample.
Header Gets	Number of times the rollback segment's header was accessed since the last sample.
Header Waits	Number of times a process had to wait to access the rollback segment's header since the last sample.
Optimal Size	Optimal size of the rollback segment.
HWM Size	High water mark for the rollback segment (the largest size the rollback segment has grown to), in bytes.
Average Active	Current average size of active extents (extents that contain uncommitted transaction data), in bytes.
Average Shrink	Total size of freed extents divided by number of shrinks, in bytes.
Wraps	Number of times the rollback segment wraps from one extent to another.
Extends	Number of times the rollback segment was extended and allocated a new extent.
Shrinks	Number of times the rollback segment shrank, deallocating one or more extents.