EVI maintenance
There are unique challenges to maintaining EVIs. The following
table shows a progression of how EVIs are maintained and the conditions under
which EVIs are most effective and where EVIs are least effective based on
the EVI maintenance characteristics.
Table 1. EVI Maintenance Considerations| |
Condition |
Characteristics |
|---|
|
Most Effective
Least Effective |
When inserting an existing distinct key value |
- Minimum overhead
- Symbol table key value looked up and statistics updated
- Vector element added for new row, with existing byte code
|
| When inserting a new distinct key value - in
order, within byte code range |
- Minimum overhead
- Symbol table key value added, byte code assigned, statistics assigned
- Vector element added for new row, with new byte code
|
| When inserting a new distinct key value - out of order,
within byte code range |
- Minimum overhead if contained within overflow area threshold
- Symbol table key value added to overflow area, byte code assigned, statistics
assigned
- Vector element added for new row, with new byte code
- Considerable overhead if overflow area threshold reached
- Access path validated - not available
- EVI refreshed, overflow area keys incorporated, new byte codes assigned
(symbol table and vector elements updated)
|
| When inserting a new distinct key value - out of byte
code range |
- Considerable overhead
- Access plan invalidated - not available
- EVI refreshed, next byte code size used, new byte codes assigned (symbol
table and vector elements updated
|