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    <p>Internally, Redis stores strings in the most efficient manner. Forcing integers into radix 10 strings will actually use more memory.</p> <p>Here is how Redis stores Strings - </p> <ol> <li>Integers less than 10000 are stored in a shared memory pool, and don't have any memory overheads. If you wish, you can increase this limit by changing the constant <a href="https://github.com/antirez/redis/blob/unstable/src/redis.h#L82">REDIS_SHARED_INTEGERS in redis.h</a> and recompiling Redis.</li> <li>Integers greater than 10000 and within range of a long consume 8 bytes. </li> <li>Regular strings take len(string) + 4 bytes for length + 4 bytes for marking free space + 1 byte for null terminator + 8 bytes for malloc overheads. </li> </ol> <p>In the example you quoted, its a question of 8 bytes for a long v/s 21 bytes for the string.</p> <p>EDIT :</p> <blockquote> <blockquote> <p>So if I have a set of numbers all less than 10,000 how does Redis store my set?</p> </blockquote> </blockquote> <p>It depends on how many elements you have.</p> <p>If you have less than 512 elements in your set (see <code>set-max-intset-entries</code>), then the set will be stored as an IntSet. An IntSet is a glorified name for a Sorted Integer Array. Since your numbers are less than 10000, it would use 16 bits per element. It is (almost) as memory efficient as a C array.</p> <p>If you have more than 512 elements, the set becomes a HashTable. Each element in the set is wrapped in a structure called <code>robj</code>, which has an overhead of 16 bytes. The <code>robj</code> structure has a pointer to the shared pool of integers, so you don't pay anything extra for the integer itself. And finally, the <code>robj</code> instances are stored in the hashtable, and the hashtable has an overhead that is proportional to the size of the set. </p> <p>If you are interested in exactly how much memory an element consumes, run <a href="https://github.com/sripathikrishnan/redis-rdb-tools">redis-rdb-tools</a> on your dataset. Or you can read the sourcecode for the class <a href="https://github.com/sripathikrishnan/redis-rdb-tools/blob/master/rdbtools/memprofiler.py#L80">MemoryCallback</a>, the comments explain how the memory is laid out.</p>
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    1. POMemory efficient way to store 32 bit signed integer in Redis
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    1. COThank you for your answer. Would you please explain just a bit more about the shared memory pool. So if I have a set of numbers all less than 10,000 how does Redis store my set ?
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    2. CO@Aresn - See updates to my answer. If you are storing sets of integers less than 10000, Redis will be very efficient memory wise.
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    3. CO@sripathi-krishnan couldn't you plz specify how much bytes are used to store string keys? Is "len()+4+4+1+8 byte" applied only to values? We need to store a really big data set of pairs string(43)=>int and need to evaluate the volume. Thanks anyway for the info!
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      1. USAlexander Palamarchuk
 

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