High memory usage on // substitution in one situation, normal usage in other

[Sebastian Gniazdowski <psprint@zdharma.org>]

Hello,
following will cause like 55 GB of VIRT memory usage (process will be killed), having RES memory at 1.8 MB, which roughly equals to ${#__text}.

local -A arr2
for (( i=1; i<=200000; i++ )); do arr2[$i]="_"; done
elems=( "${(kv@)arr2}" )
__text=${elems[*]}
echo ${#__text}
1688894
__text="${__text//(#b)([^$'\03'-$'\07'$'\013'-$'\014'$'\016'-$'\031'$'0\037']##)/${(q)match[1]}}"

Follwing will work smoothly:

arr=( ${(s::)${(r:900000::_:)empty}} )
__text=${arr[*]}
echo ${#__text}
1799999
__text="${__text//(#b)([^$'\03'-$'\07'$'\013'-$'\014'$'\016'-$'\031'$'0\037']##)/${(q)match[1]}}"

I wonder why there is a difference between those two scenarios, why VIRT raises and RES doesn't, and why VIRT rise happens?

--
Sebastian Gniazdowski
psprint /at/ zdharma.org