The flood of fresh debt, sold by governments to fund pandemic-rescue packages, threatens to dwarf central-bank buying and swamp markets in the U.K., Canada and Australia, according to Bloomberg calculations. Policy-maker purchases will also lag issuance in the U.S. and Japan, where a continuing tilt toward buying short-maturity debt would risk allowing yields on longer-dated bonds to rise unchecked, hurting pension funds and life insurers that rely on these markets.