  We perform an extensive study of autocorrelation of several observables in
lattice QCD with two degenerate flavours of naive Wilson fermions and
unimproved Wilson gauge action using DD-HMC algorithm. We show that (1) at a
given lattice spacing, autocorrelation of topological susceptibility decreases
with decreasing quark mass and autocorrelations of plaquette and Wilson loop do
not increase with decreasing quark mass, (2) autocorrelation of topological
susceptibility substantially increases with decreasing lattice spacing but
autocorrelation of topological charge density correlator shows only mild
increase and (3) increasing the size and the smearing level increase the
autocorrelation of Wilson loop.
