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BITOP

Syntax​

BITOP <AND | OR | XOR | NOT> destkey key [key ...]

Time complexity: O(N)

ACL categories: @write, @bitmap, @slow

Perform a bitwise operation between multiple keys (containing string values) and store the result in the destination key.

The BITOP command supports four bitwise operations: AND, OR, XOR and NOT, thus the valid forms to call the command are:

  • BITOP AND destkey srckey1 srckey2 srckey3 ... srckeyN
  • BITOP OR destkey srckey1 srckey2 srckey3 ... srckeyN
  • BITOP XOR destkey srckey1 srckey2 srckey3 ... srckeyN
  • BITOP NOT destkey srckey

As you can see NOT is special as it only takes an input key, because it performs inversion of bits so it only makes sense as a unary operator.

The result of the operation is always stored at destkey.

Handling of strings with different lengths​

When an operation is performed between strings having different lengths, all the strings shorter than the longest string in the set are treated as if they were zero-padded up to the length of the longest string.

The same holds true for non-existent keys, that are considered as a stream of zero bytes up to the length of the longest string.

Return​

Integer reply: the size of the string stored in the destination key, which is equal to the size of the longest input string.

Examples​

dragonfly> SET key1 "foobar"
OK
dragonfly> SET key2 "abcdef"
OK
dragonfly> BITOP AND dest key1 key2
(integer) 6
dragonfly> GET dest
"`bc`ab"

Pattern: real time metrics using bitmaps​

BITOP is a good complement to the pattern documented in the BITCOUNT command documentation. Different bitmaps can be combined in order to obtain a target bitmap where the population counting operation is performed.

Performance considerations​

BITOP is a potentially slow command as it runs in O(N) time. Care should be taken when running it against long input strings.

For real-time metrics and statistics involving large inputs a good approach is to use a replica (with replica-read-only option enabled) where the bit-wise operations are performed to avoid blocking the master instance.