Every block in the file has a corresponding bit in a bitmap. All blocks with valid data are marked busy in their maps; all blocks that are unused or no longer hold data are marked free. GDS uses bitmaps to locate free blocks efficiently. The errors discussed in this section indicate problems with bitmaps.
"Block incorrectly marked free" is the only potentially dangerous bitmap error. This error means that the block is within the B-tree structure, but that the bitmap shows it available for use (i.e., it is a "Block doubly allocated" waiting to happen). Immediately use DSE to MAP such blocks BUSY.
Bitmap information is redundant (i.e., bitmaps can be recreated by scanning the B-tree); however, the majority of bitmap errors reflect secondary errors emanating from flaws in the B-tree, which are often reported as key or data errors by MUPIP INTEG.
When INTEG encounters an error, it stops processing that leaf of the tree. When it subsequently compares its generated bitmaps to those in the database, it reports the blocks belonging in the tree that it could not find as "Block incorrectly marked busy." This error type can be viewed as a flag, marking the location of a block of lost data whose index is disrupted.
INTEG reports each block that it concludes is incorrectly marked, and also the local map that holds the "bad" bits. Furthermore, if the local map "errors" affect whether the local map should be marked full or not full in the master map, INTEG also reports the (potential) problem with the master map. Therefore, a single error in a level one (1) index block will generate, in addition to itself, one or more "Block incorrectly marked busy", one or more "Local bitmap incorrect", and possibly one or more "Master bitmap shows..." Errors in higher level index blocks can induce very large numbers of bitmap error reports.
Because bitmap errors are typically secondary to other errors, correcting the primary errors usually also cures the bitmap errors. For this reason and, more importantly, because bitmap errors tend to locate "lost" data, they should always be corrected at, or close to, the end of a repair session.
The DSE command MAP provides a way to switch bits in local maps with FREE and BUSY, propagate the status of a local map to the master map with MASTER, and completely rebuild all maps from the B-tree with RESTORE. Never use MAP MASTER until all non-bitmap errors have been resolved.