Tasks
1)Add a field in Pair struct to indicate weather the node was inserted due to pre-warming or due to normal load.


Results
1)On real1 dataset
1.1)Over the period of 20 minutes after failure, there are 212k evictions from single_pool
1.2)Over the period of 20 minutes after failure, there are 589k evictions from multi_pool
1.3)Over the period of 20 minutes after failure, there are 801k evictions in total
1.4)Over the period of 20 minutes after failure, there are 201k evictions of pre-warmed objects. so almost 25% of the evictions
1.5)Almost all the 201k evictions of pre-warmed objects happen in the first 5 minutes. So essentially there are no prewarmed objects 
in the cache after first 5 minutes -> this seems to be bad. try reducing pre-warming size(50%? maybe)
1.6)In first 5 minutes 171k/235k evictions are of pre-warmed objects
1.7)Another idea could be to stop pre-warming once the first pre-warmed object is evicted -> try this. idea seems interesting but can such thing be done iun actual setting?
1.8)prewarming size of 50% gives slightly better results
1.9)Another possible idea could be to fix the prewarm set size and then prewarm in reverse order. so that important objects are at the back of the queue
1.10)Analyse trace carefulle for locality
1.11)estimate how many objects can fit in cache