Small values
An 8 byte value under a 30 byte key, where overhead is most of the cost
keys: 1000000 key-bytes: 30 value-bytes: 8
Redis Key Count to Memory
Give an average key and value size and see the total at several scales, plus how much of it is overhead rather than data.
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Wanted a different tool?
- Redis Memory Calculator if the keys hold hashes, sets or lists rather than plain strings, because then the encoding decides the answer and a per-key figure will understate it.
Examples
Real input you can load into the tool above. Each one shows a different thing going wrong, because that is what the tool is for.
Larger values
A 1 KB value, where the data dominates and overhead is noise
keys: 1000000 key-bytes: 30 value-bytes: 1024
Common mistakes
These are the ones that fail silently. The config is accepted, nothing raises an error, and the consequence arrives later.
Storing many small values as separate keys
Each pays the full per-key cost. A hundred keys of 8 bytes costs far more than one hash with a hundred fields.
Instead:Group related values into a hash, which pays the per-key overhead once.
Using long descriptive key prefixes
The name is stored in full per key, forever. A 60 byte prefix across ten million keys is 600 MB of prefix.
Instead:Shorten the prefix. The saving is exact and permanent.
Forgetting the dictionary itself
The main hash table sizes to a power of two, so it is between one and two pointers per key on top of the entry.
Instead:Budget for it. It is invisible in any calculation based on key and value size alone.
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