Without this index we got errors like:

[root@p06253947b39467 ~]# cta af ls --instance cta --path /eos/dev/test/gcancio/10072017/file_2167
Failed to execute the command. Reason: Failed to open root://10.16.135.81:10955//Y3Rh&YWY=&bHM=&LS1pbnN0YW5jZQ==&Y3Rh&LS1wYXRo&L2Vvcy9kZXYvdGVzdC9nY2FuY2lvLzEwMDcyMDE3L2ZpbGVfMjE2Nw==: [ERROR] Operation expired
[root@p06253947b39467 ~]#

With this index we execute the same query in less than a second:

[root@p06253947b39467 ~]# time cta af ls --instance cta --path /eos/dev/test/gcancio/10072017/file_2167
 289440       1  I20170    1381    51096      cta   18965         1006       ADLER32     0XFBA23F1D    german_raw  gcancio       c3    1499697578 /eos/dev/test/gcancio/10072017/file_2167

real    0m0.590s
user    0m0.005s
sys    0m0.006s
[root@p06253947b39467 ~]#