If there are 59 news items, the last merged indexing files should be 
 [tier_5_A, tier_2_A, tier_1_A] 
 "B" file will never appear, because once it appears, it is merged.
 
 tier_1_A=1 file
 tier_2_A=2 files
 tier_5_A=16 files

 (16+2+1)*3 =57
 57+2(still in the memory) = 59

If there are 59 news items, the last merged indexing files should be [tier_5_A, tier_2_A, tier_1_A] "B" file will never appear, because once it appears, it is merged. tier_1_A=1 file tier_2_A=2 files tier_5_A=16 files (16+2+1)*3 =57 57+2(still in the memory) = 59