Try this
| gentimes start=-1 | eval s="[11/Dec/2015:04:45:26 +481] Topic1_0=[9,7,2] Topic1_1=[3,2,1] Topic1_2=[6,4,2] Topic1_3=[2,1,1]
[11/Dec/2015:04:45:26 +481] Topic2_0=[5,3,2] Topic2_1=[2,1,1] Topic2_2=[0,0,0] Topic2_3=[1,1,0]"
| rex max_match=0 field=s "\]\s(?<top>\w+)_\d=\[(?<prod>\d+),(?<cons>\d+),(?<lag>\d+)"
| eval z=mvzip(top, prod) | eval z=mvzip(z, cons) | eval z=mvzip(z, lag)
| mvexpand z
| eval t=split(z, ",")
| eval Topic=mvindex(t, 0) | eval prod=mvindex(t, 1) | eval cons=mvindex(t, 2) | eval lag=mvindex(t, 3)
| stats sum(prod) as Produced, sum(cons) as Consumed, sum(lag) as Lag by Topic
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