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BF.RESERVE

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BF.RESERVE key error_rate capacity [EXPANSION expansion] [NONSCALING]
Group
Bloom filter
Complexity
O(1)
Arity
-1 (at least 1 words, counting the command name)
Flags
fast
Keys
first 1, last 1, step 1
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BF.RESERVE creates an empty Bloom filter at key. A Bloom filter answers “have I seen this item?” using far less memory than a set: it never misses an item that was added, but may wrongly report an item that was not, at about the error rate you choose.

You only need BF.RESERVE to pick non-default settings. BF.ADD, BF.MADD and BF.INSERT create a filter on demand, with capacity 100, error rate 0.01 and expansion 2.

Arguments and options

Section titled “Arguments and options”
Argument Effect
error_rate The false positive rate to aim for, between 0 and 1 (exclusive), for example 0.001 for 0.1%. Lower rates use more memory.
capacity How many items the filter is sized for, from 1 to 1073741824.
EXPANSION expansion When the filter is full, the next item adds a new layer this many times larger than the last one, keeping the overall error rate. Default 2, range 0 to 32768. 0 makes the filter non-scaling.
NONSCALING Never grow: once capacity items are in, adding a new item fails.

EXPANSION and NONSCALING cannot be combined. Other extra arguments are ignored.

Return value

Section titled “Return value”
Case RESP2 RESP3
Created Simple string OK Simple string OK

Error replies:

  • ERR item exists if a Bloom filter already exists at the key.
  • ERR bad error rate and ERR error rate must be in the range (0.000000, 1.000000)
  • ERR bad capacity and ERR capacity must be in the range [1, 1073741824]
  • ERR no expansion, ERR bad expansion and ERR expansion must be in the range [0, 32768]
  • Nonscaling filters cannot expand when EXPANSION and NONSCALING are both given.
  • ERR Insufficient memory to create filter when the filter would not fit in memory.
  • WRONGTYPE if the key holds another type.

Examples

Section titled “Examples”
127.0.0.1:6379> BF.RESERVE signups 0.01 1000
OK
127.0.0.1:6379> BF.RESERVE signups 0.01 1000
(error) ERR item exists
127.0.0.1:6379> BF.RESERVE fixed 0.001 5000 NONSCALING
OK
127.0.0.1:6379> BF.RESERVE bad 1.5 100
(error) ERR error rate must be in the range (0.000000, 1.000000)

Compatibility

Section titled “Compatibility”

Same arguments, limits and errors as BF.RESERVE in RedisBloom.

See also

Section titled “See also”

BF.ADD, BF.INSERT, BF.INFO, BF.EXISTS