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INCRBY

Introduction​

In Dragonfly, as well as in Redis and Valkey, the INCRBY command allows you to increment the value of a key by a specified integer amount. This is particularly useful when working with counters or any numerical values that need to be incremented atomically. If the key does not exist, INCRBY will create the key with an initial value of 0 before performing the increment operation.

Syntax​

INCRBY key increment
  • Time complexity: O(1)
  • ACL categories: @write, @string, @fast

Parameter Explanations​

  • key: The name of the key whose value you want to increment.
  • increment: The integer amount by which to increment the current value at the key.

Return Values​

The command returns the new value of the key, which is the result of adding the specified increment to the current value.

Code Examples​

Basic Example​

Increment a key by 5:

dragonfly> SET mycounter 10
OK
dragonfly> INCRBY mycounter 5
(integer) 15

In this example, the value of mycounter is initially 10, and after executing INCRBY mycounter 5, the new value becomes 15.

Increment a Non-Existent Key​

If the key does not exist, INCRBY will first set it to 0 and then increment it by the specified value:


dragonfly> INCRBY newcounter 4
(integer) 4

Here, newcounter did not exist initially. INCRBY creates the key and sets its value to 4 as there was no existing value to increment.

Using Negative Increments​

You can also decrement a key by passing a negative number as the increment value:

dragonfly> SET score 20
OK
dragonfly> INCRBY score -7
(integer) 13

In this example, INCRBY is used with a negative value of -7 to decrement the key score from 20 to 13.

Multiple Increments​

Increment the same key multiple times with different values:

dragonfly> SET visits 100
OK
dragonfly> INCRBY visits 10
(integer) 110
dragonfly> INCRBY visits 15
(integer) 125

Here, the value of visits is incremented twice, first by 10 and then by 15, resulting in a final value of 125.

Best Practices​

  • Use INCRBY for maintaining counters or other numeric accumulations that need to be updated atomically.
  • Keep in mind that if you are dealing with non-integer values, this command does not support floating-point numbers. For floats, use INCRBYFLOAT instead.

Common Mistakes​

  • Applying INCRBY to a key that holds a non-integer value will result in an error. Ensure that the key either contains an integer or does not exist when using this command.

  • Using INCRBY with a key that stores a non-numeric value will cause an error and fail:

    dragonfly> SET mystring "hello"
    OK
    dragonfly> INCRBY mystring 2
    (error) ERR value is not an integer or out of range

  • Trying to increment large numerical values that exceed the 64-bit signed integer limit may result in an overflow error.

FAQs​

What happens if the key holds a string value instead of an integer?​

If the key holds a string, list, or another non-integer value, INCRBY will return an error. The key must either be unset or holding an integer value to execute successfully.

Can I use INCRBY with floating-point numbers?​

No, INCRBY only works with integers. If you need to increment by a floating-point number, you should use the INCRBYFLOAT command.

What’s the maximum increment value I can use?​

INCRBY supports 64-bit signed integers. As such, the maximum allowable increment would be 9,223,372,036,854,775,807, and the minimum would be -9,223,372,036,854,775,808.