Query Cache utilisation ~50% Qcache_lowmem_prunes still high I ran two tests, each running for about a week

Test 1

Query Cache Settings


query_cache_limit: 50K
query_cache_size: 128M
query_cache_min_res_unit: 1K


Results


Qcache_free_blocks: 6,004
Qcache_free_memory: 93,598,504
Qcache_hits: 377,204,411
Qcache_inserts: 13,056,941
Qcache_lowmem_prunes: 384,610
Qcache_not_cached: 5,794,907
Qcache_queries_in_cache: 16,006
Qcache_total_blocks: 38,724


Results (Calculated Values)


Utilisation: 40.7%
Removal Ratio: 2.9%
Hit Rate: 95.2%
AVG Query Size: 4,012
Frag Indicator: 15.5%



Utilisation = 100-Qcache_free_memory*100/query_cache_size
Removal Ratio = Qcache_lowmem_prunes*100/Qcache_inserts
Hit Rate = Qcache_hits*100/(Qcache_hits+Qcache_inserts+Qcache_not_cached)
AVG Query Size = (query_cache_size - Qcache_free_memory) / Qcache_queries_in_cache
Frag Indicator = Qcache_free_blocks*100/Qcache_total_blocks


Test 2

Query Cache Settings

same as above except


query_cache_min_res_unit: 2K


Results


Qcache_free_blocks: 1,287
Qcache_free_memory: 70,082,320
Qcache_hits: 223,742,107
Qcache_inserts: 7,104,530
Qcache_lowmem_prunes: 186,235
Qcache_not_cached: 3,218,864
Qcache_queries_in_cache: 20,802
Qcache_total_blocks: 43,424


Results (Calculated Values)


Utilisation: 55.6%
Removal Ratio: 2.6%
Hit Rate: 95.6%
AVG Query Size: 4,217
Frag Indicator: 3.0%


now for the question....

As expected, when I lowered query_cache_min_res_unit, fragmentation went up. What really has me confused is why is the removal ratio still so high even when utilisation is low?
To use least amount of QC space, use

query_cache_min_res_unit=512 


for less waste of QC RAM  and qcache_lowmem_prunes expected to decrease as well over time.