BF.SCANDUMP

Syntax

BF.SCANDUMP key iterator

Time complexity: O(F + C) per call, where F is the number of sub-filters and C is the number of bytes returned.

ACL categories: @bloom

Exports the Bloom filter stored at key as a sequence of binary chunks. Use BF.LOADCHUNK to restore those chunks into a Bloom filter.

Iteration

Start with iterator set to 0. Each call returns an iterator and a data chunk. Pass the returned iterator to the next BF.SCANDUMP call. Continue until the returned iterator is 0, which indicates completion and is accompanied by an empty string.

Treat iterators as opaque values: use the values returned by the command rather than calculating them yourself. Preserve each nonzero returned iterator together with its chunk. To restore the filter, pass these pairs to BF.LOADCHUNK destination iterator data in the order they were returned. Do not pass the final zero iterator and empty string to BF.LOADCHUNK.

The chunks contain binary data, so use a client that preserves bytes without decoding them as text. Keep the source filter unchanged throughout the dump; the sequence of calls does not provide a snapshot across concurrent updates.

Return

Array reply with two elements:

1. Integer reply: the iterator for the next call, or 0 when the dump is complete.
2. Bulk string reply: the binary data chunk, or an empty string when the dump is complete.

Error reply: if key does not exist, holds a different data type, is a Bloom filter still being loaded, or iterator is not a nonnegative signed 64-bit integer.

Examples

Create a filter and start its dump:

dragonfly> BF.RESERVE visitors 0.01 1000
OK

dragonfly> BF.MADD visitors alice bob carol
1) (integer) 1
2) (integer) 1
3) (integer) 1

dragonfly> BF.SCANDUMP visitors 0
1) (integer) 1
2) "\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00@"

The first reply contains metadata. Continue with the returned iterator to obtain the filter data. The following Python example uses the redis package to copy the filter created above into a new key, visitors-copy. Use a destination key that does not already exist.

import redis

client = redis.Redis(host="localhost", port=6379, decode_responses=False)

iterator = 0
while True:
    iterator, data = client.execute_command("BF.SCANDUMP", "visitors", iterator)
    if iterator == 0:
        break
    client.execute_command("BF.LOADCHUNK", "visitors-copy", iterator, data)

print(client.execute_command("BF.MEXISTS", "visitors-copy", "alice", "bob", "carol"))
# [1, 1, 1]

See also

BF.LOADCHUNK | BF.RESERVE | BF.INFO | BF.MEXISTS