Assuming this precise sequence of host and sid is the deciding criterion, maybe something like
Code:
sed '/host=atlx3 sid=atld3/{;h;s/^/#/p;x;}' abc.txt
This takes a matching line and remembers it in the
hold space (h); then substitutes a hash mark at beginning of line and prints the result; then swaps back the hold space (x) which will be printed as any other line a second time.