- Prior to ALTIBASE HDB 5.5.1, only ALLOC of undo tablespace could be checked, but USED could not be checked.
- This chapter describes how to check the actual usage tablespaces using V$DISK_UNDO_USAGE added from ALTIBASE HDB version 5.5.1.
ALLOC and USED of undo tablespace
- The undo tablespace is made up of segments, and segments are made up of smaller units called extents.
- When a change transaction occurs in a disk table, it is allocated in units of extents. Whenever an extent is newly allocated, the size of the undo tablespace ALLOC increases.
- When the transaction ends, the extent becomes reusable.
- However, if any of the extents within a segment are in use, even if there are reusable extents, all of the extents within that segment become unusable. (UNSTEALABLE EXTENT)
- Either the extent is used because a change transaction is executing, or the UNSTEALABLE extent is counted as USED for the undo tablespace.
This monitoring query is available in the version below.
- ALTIBASE HDB 5.5.1
- ALTIBASE HDB 6.1.1
- ALTIBASE HDB 6.3.1
Undo tablespace usage
- ALLOC and USED may increase while a change transaction is being performed on the disk table.
- If the transaction is committed, the USED that is increased during the execution of the transaction is reduced.
- If the transaction is rolled back, the ALLOC and USED that have increased during the execution of the transaction will be reduced.
- Improved the problem of calculating undo areas that cannot be reused as usable space. (A problem in which the extent corresponding to the UNSTEALABLE_EXT_CNT column is calculated as the available extent)
- Refer to the description of the V$DISK_UNDO_USAGE performance view below for the UNSTEALABLE_EXT_CNT column.
- ALTIBASE HDB 18.104.22.168.9
- ALTIBASE HDB 22.214.171.124.3
Reference - V$DISK_UNDO_USAGE performance view
Number of extents for a segment (Transaction Status Segment, TSS) that stores transaction status information.
Number of extents in the undo segment being used in the transaction.
Number of extents that cannot be taken from other undo segments.
Number of reusable extents
The total number of extents allocated from the undo tablespace.