redis bitop命令

BITOP operation destkey key [key …]

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 an 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.


Integer reply

The size of the string stored in the destination key, that is equal to the
size of the longest input string.


redis>  SET key1 “foobar”


redis>  SET key2 “abcdef”


redis>  BITOP AND dest key1 key2

(integer) 6

redis>  GET dest


*Pattern: real time metrics using bitmaps

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

See the article called “Fast easy realtime metrics using Redis
” for a interesting use cases.

*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 slave (with read-only option disabled) where the bit-wise
operations are performed to avoid blocking the master instance.