DEDB insert algorithm
The DEDB insert algorithm searches for additional space when space is not available in the most desirable block.
This topic contains Diagnosis, Modification, and Tuning information.
For root segments, if the RAP CI does not have sufficient space to hold the entire record, it contains the root and as many direct dependents as possible. Base CIs that are not randomizer targets go unused. The algorithm next searches for space in the first dependent overflow CI for this UOW. From the header of the first dependent overflow CI, a determination is made whether space exists in that CI.
If the CI pointed to by the current overflow pointer does not have enough space, the next dependent overflow CI (if one exists) is searched for space. The current overflow pointer is updated to point to this dependent overflow CI. If no more dependent overflow CIs are available, then the algorithm searches for space in the independent overflow part.
When an independent overflow CI has been selected for storing data, it can be considered a logical extension of the overflow part for the UOW that requested it.
The following figure shows how a UOW is extended into independent overflow. This UOW, defined as 10 CIs, includes 8 Base CIs and 2 dependent overflow CIs. Additional space is needed to store the database records that randomize to this UOW. Two independent overflow CIs have been acquired, extending the size of this UOW to 12 CIs. The first dependent overflow CI has a pointer to the second independent overflow CI indicating that CI is the next place to look for space.
