Event counters
Track page views, API requests, downloads, or other event totals in a hash.
Redis · Module
HINCRBY
HINCRBY adds a signed integer to a field in a Redis hash and returns the updated value. Missing hashes and fields are created automatically, with a missing field starting at zero.
How it works
HINCRBY adds a signed integer to a field in a Redis hash and returns the field's new value. Redis creates the hash when its key is absent and treats an absent field as zero before applying the increment; values must fit a signed 64-bit integer.
Syntax
HINCRBY key field incrementParameters
| Name | Type | Description |
|---|---|---|
key | key | The name of the key that holds the hash. |
field | field | The field whose value to increment. |
increment | signed 64-bit integer | The integer amount to add to the field's value. |
Returns
An integer reply containing the field's value after the increment operation.
Key points
- It updates one hash field by adding the supplied integer increment.
- A missing hash key is automatically created as part of the operation.
- A missing field starts at zero before the increment is applied.
- Positive and negative increments support both increasing and decreasing counters.
- The response is the field's new integer value, not the previous value.
Common mistakes
- The increment and resulting value must remain within the signed 64-bit integer range.
Example: Increment and decrement a hash counter
HSET counters page_views 10
HINCRBY counters page_views 1
HINCRBY counters page_views -2
HGET counters page_viewsCreates a numeric hash field, increments it, decrements it, then reads the resulting value.
When to use it
Quantity updates
Adjust inventory or balance-like integer quantities by positive or negative amounts.
Grouped metrics
Maintain several related integer counters under one Redis hash key.
Interview questions
QWhat does HINCRBY do?
HINCRBY takes a hash key, a field name, and a signed integer increment. It returns the field value after applying the operation.
Follow-up: What happens when either the hash key or field is missing? Redis creates the hash if the key is absent and initializes the missing field to zero.
QCan HINCRBY decrement a value?
The command supports negative increments, so it can decrement a counter as well as increment one. The returned integer is the updated field value.
Follow-up: How would you decrement by 10? Use HINCRBY key field -10.
QWhat are HINCRBY's complexity and numeric limits?
HINCRBY has O(1) time complexity. The increment argument and resulting value are constrained to signed 64-bit integers.
Follow-up: What should be used for decimal values? Use the separate HINCRBYFLOAT command, which is intended for floating-point hash fields.
Related
HDECRBYHINCRBYFLOATHGETHSET