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?