In Redis, using Hash data type over String data type save half the memory.

redis_experiment

jruby-1.7.1 :079 > redis_conn
 => #<Redis client v3.0.2 for redis://localhost:6379/0> 
jruby-1.7.1 :080 > redis_conn.flushdb
 => "OK" 
jruby-1.7.1 :081 > redis_conn.info "memory"
 => {"used_memory"=>"1081696", "used_memory_human"=>"1.03M", "used_memory_rss"=>"29933568", "used_memory_peak"=>"38219840", "used_memory_peak_human"=>"36.45M", "used_memory_lua"=>"31744", "mem_fragmentation_ratio"=>"27.67", "mem_allocator"=>"libc"} 
jruby-1.7.1 :082 > 100000.times { |i| redis_conn.mset "USER"+i.to_s+"POSTS",(1+i).to_s, "USER"+i.to_s+"COMMENTS"+i.to_s,(2+i).to_s, "USER"+i.to_s+"LIKES"+i.to_s,(2+i).to_s, "USER"+i.to_s+"DISLIKES"+i.to_s,(2+i).to_s}
 => 100000 
jruby-1.7.1 :083 > redis_conn.info "memory"
 => {"used_memory"=>"36636112", "used_memory_human"=>"34.94M", "used_memory_rss"=>"42246144", "used_memory_peak"=>"38219840", "used_memory_peak_human"=>"36.45M", "used_memory_lua"=>"31744", "mem_fragmentation_ratio"=>"1.15", "mem_allocator"=>"libc"} 
jruby-1.7.1 :084 > redis_conn.flushdb
 => "OK" 
jruby-1.7.1 :085 > redis_conn.info "memory"
 => {"used_memory"=>"1081824", "used_memory_human"=>"1.03M", "used_memory_rss"=>"29749248", "used_memory_peak"=>"38219840", "used_memory_peak_human"=>"36.45M", "used_memory_lua"=>"31744", "mem_fragmentation_ratio"=>"27.50", "mem_allocator"=>"libc"} 
jruby-1.7.1 :086 > 100000.times { |i| redis_conn.hmset "USER"+i.to_s, "USER"+i.to_s+"POSTS",(1+i).to_s, "USER"+i.to_s+"COMMENTS"+i.to_s,(2+i).to_s, "USER"+i.to_s+"LIKES"+i.to_s,(2+i).to_s, "USER"+i.to_s+"DISLIKES"+i.to_s,(2+i).to_s}
 => 100000 
jruby-1.7.1 :087 > redis_conn.info "memory"
 => {"used_memory"=>"22387968", "used_memory_human"=>"21.35M", "used_memory_rss"=>"30986240", "used_memory_peak"=>"38219840", "used_memory_peak_human"=>"36.45M", "used_memory_lua"=>"31744", "mem_fragmentation_ratio"=>"1.38", "mem_allocator"=>"libc"} 
jruby-1.7.1 :088 > redis_conn.flushdb
 => "OK" 
jruby-1.7.1 :089 > redis_conn.info "memory"
 => {"used_memory"=>"1081952", "used_memory_human"=>"1.03M", "used_memory_rss"=>"30253056", "used_memory_peak"=>"38219840", "used_memory_peak_human"=>"36.45M", "used_memory_lua"=>"31744", "mem_fragmentation_ratio"=>"27.96", "mem_allocator"=>"libc"} 
jruby-1.7.1 :090 > 100000.times { |i| redis_conn.hmset "USER"+i.to_s, "POSTS",(1+i).to_s, "COMMENTS"+i.to_s,(2+i).to_s, "LIKES"+i.to_s,(2+i).to_s, "DISLIKES"+i.to_s,(2+i).to_s}
 => 100000 
jruby-1.7.1 :091 > redis_conn.info "memory"
 => {"used_memory"=>"18112928", "used_memory_human"=>"17.27M", "used_memory_rss"=>"30470144", "used_memory_peak"=>"38219840", "used_memory_peak_human"=>"36.45M", "used_memory_lua"=>"31744", "mem_fragmentation_ratio"=>"1.68", "mem_allocator"=>"libc"}