content/commands/bf.reserve.md
Creates an empty Bloom filter with a single sub-filter for the initial specified capacity and with an upper bound error_rate.
By default, the filter auto-scales by creating additional sub-filters when capacity is reached.
The new sub-filter is created with size of the previous sub-filter multiplied by expansion.
Though the filter can scale up by creating sub-filters, it is recommended to reserve the estimated required capacity since maintaining and querying
sub-filters requires additional memory (each sub-filter uses an extra bits and hash function) and consume further CPU time than an equivalent filter that had
the right capacity at creation time.
The optimal number of hash functions is ceil(-ln(error_rate) / ln(2)).
The required number of bits per item, given the desired error_rate and the optimal number of hash functions, is -ln(error_rate) / ln(2)^2. Hence, the required number of bits in the filter is capacity * -ln(error_rate) / ln(2)^2.
is key name for the the Bloom filter to be created.
</details> <details open><summary><code>error_rate</code></summary>The desired probability for false positives. The rate is a decimal value between 0 and 1. For example, for a desired false positive rate of 0.1% (1 in 1000), error_rate should be set to 0.001.
</details> <details open><summary><code>capacity</code></summary>The number of entries intended to be added to the filter.
If your filter allows scaling, performance will begin to degrade after adding more items than this number.
The actual degradation depends on how far the limit has been exceeded. Performance degrades linearly with the number of sub-filters.
Prevents the filter from creating additional sub-filters if initial capacity is reached.
Non-scaling filters requires slightly less memory than their scaling counterparts. The filter returns an error when capacity is reached.
When capacity is reached, an additional sub-filter is created.
The size of the new sub-filter is the size of the last sub-filter multiplied by expansion, specified as a positive integer.
If the number of items to be stored in the filter is unknown, you use an expansion of 2 or more to reduce the number of sub-filters.
Otherwise, you use an expansion of 1 to reduce memory consumption. The default value is 2.
{{< highlight bash >}} redis> BF.RESERVE bf 0.01 1000 OK {{< / highlight >}}
{{< highlight bash >}} redis> BF.RESERVE bf 0.01 1000 (error) ERR item exists {{< / highlight >}}
{{< highlight bash >}} redis> BF.RESERVE bf_exp 0.01 1000 EXPANSION 2 OK {{< / highlight >}}
{{< highlight bash >}} redis> BF.RESERVE bf_non 0.01 1000 NONSCALING OK {{< / highlight >}}
| Redis Software | Redis Cloud | <span style="min-width: 9em; display: table-cell">Notes</span> | |:----------------------|:-----------------|:------| | <span title="Supported">✅ Supported</span> | <span title="Supported">✅ Flexible & Annual</span> <span title="Supported">✅ Free & Fixed</nobr></span> | |
{{< multitabs id="bf-reserve-return-info" tab1="RESP2" tab2="RESP3" >}}
One of the following:
OK if the filter was created successfully.-tab-sep-
One of the following:
OK if the filter was created successfully.{{< /multitabs >}}