The previous code would update the latest index only, even
if the metric is on another one. Now we fetch the latest document
and we update read_on on this one.
Coverage decreased (-0.1%) to 81.759% when pulling 6b4b459786d642eea46c95fc93c58838e5736717 on iksaif:master into 51f73cf133f8d2cd2d2079129566fe48c83a7918 on criteo:master.
The previous code would update the latest index only, even if the metric is on another one. Now we fetch the latest document and we update read_on on this one.