What dcache is

A dcache is a storage method for data of temporary value. It's effective in terms of size and space.

What dcache is not

A dcache is not meant to hold mission-critical data which cannot be recovered. Data in a dcache may be deleted at any time, if need arises. This is not a bug but a feature.

A dcache is potentially vulnerable to corruption problems if the process writing to it is killed or crashes during some non-atomical operations. The code has been written to minimize the window during which this can happen, but still serious corruption of the index can occur.
In most of these cases dcachedump should be able to dump the content of the cache.

Applications for dcache