Can two bitcoin-qt share the same blockchain data I have a bitcoin-qt and bitcoin-abc on same computer running, can both share the same beginning of the blockchain data file ? since they both have same history till point in time.
It's not a documented feature, but Bitcoin Core and its derivatives only write to the last blk*.dat file, and only read the others.  So you can create symlinks to have them share older files.  I've done this (for testnet) and it worked fine.