Plan your fallback strategy before starting repairs with DSE.

This will enable you to make the best choice between repair and restore and/or recovery strategies as your analysis proceeds. In addition, you will be able to reasonably assess the potential risks of your decision.

Determine, at least approximately, the extent of the damage, and how much work has been done since the last backup.

Check the existence, dates, and sizes of all files; do not assume that everything is as it "should" be.

Estimate the time required to restore and redo the work. Determine if there are special circumstances, such as imminent deadlines.

Consider whether you have the disk space to pursue two courses in parallel.

Consider whether you should back up the damaged database for additional protection or for later analysis.

Before changing any block in the database, always use the DSE SAVE command to make an in-memory copy of that block.

If a modification fails to accomplish its intended goal, you can use the DSE RESTORE command to get the block back to its previous state. For instance, a CHANGE -BSIZ= that specifies a smaller block size causes DSE to discard all information falling beyond the new size.

An important aspect of this strategy is recognizing that testing some modifications requires using other tools such as MUPIP INTEG, but once you leave DSE to invoke MUPIP you lose anything saved in memory. To avoid this problem, use SPAWN to access those tools.

To save a copy of the block for further analysis, SAVE it, and then RESTORE it to an empty block. The best place to put such a copy, using RESTORE -REGION=, is in a special region created just to receive such blocks.

Alternatively, you can RESTORE it temporarily in a free block within the region, preferably near the end of the file. If you RESTORE the block to the original database, it may be overlaid when normal operation requires more blocks. You may prevent this overlay by using MAP -BUSY on the target block of the RESTORE. However this causes INTEG to report "incorrectly marked busy" errors.

After changing a block, always check the quality of the result by using the DSE INTEG command.

DSE INTEG does not check the placement of the block in the tree. It checks only the single block specified explicitly with the -BLOCK= qualifier or implicitly (the current block) when -BLOCK= is omitted. If you need to verify the index structure related to a block, SPAWN and use MUPIP INTEG -REGION -FAST, possibly with the -BLOCK or -SUBSCRIPT qualifiers.

Specifying -BLOCK= tends to avoid incorrect assumptions about which block DSE last handled. Not specifying -BLOCK= tends to minimize typographical errors in identifying the block.