Currently, the cfile value index blocks store the entire value for the first value in each data block. This is actually not necessary – we only need to store the shortest string that falls between the last key of the previous block and the first key of this block. For example:
Data block 1: apple,banana,cardamom
Data block 2: carrot,epazote,fennel
Today we would store:
Index block entries: ['apple' -> block 1, 'carrot' -> block 2]
Minimally, we can store:
Index block entries: ['' -> block 1, 'care' -> block 2]
In this example only a few bytes are saved, but in the case of longer key strings, the savings can be substantial. For example, if the key is a 36-byte UUID uniformly distributed, and we have 1000x32KB data blocks in a 32MB cfile, we can probably shorten the index entries to only 2-3 bytes on average for a big savings.