SETRANGE

Introduction and Use Case(s)

The SETRANGE command in Redis is used to overwrite part of a string at a specified range. This command is useful for modifying parts of an existing string without replacing the entire value, which can be beneficial when working with large strings or binary data. Typical use cases include updating specific fields within a structured string or modifying sections of a binary blob.

Syntax

SETRANGE key offset value

Parameter Explanations

• key: The name of the key that holds the string value.
• offset: The zero-based byte offset where the modification should begin.
• value: The string to be inserted starting at the specified offset.

Return Values

The SETRANGE command returns the length of the string after the modification.

Example:

(integer) 13

Code Examples

dragonfly> SET mykey "Hello World"
OK
dragonfly> SETRANGE mykey 6 "Redis"
(integer) 11
dragonfly> GET mykey
"Hello Redis"

In this example:

1. The initial value of mykey is set to “Hello World”.
2. The SETRANGE command modifies the string starting at offset 6, changing “World” to “Redis”.
3. The final string is “Hello Redis”.

Best Practices

• Ensure that the offset provided does not cause unintentional padding with null bytes, especially if the string length extends significantly.
• Use SETRANGE for modifying existing parts of a string rather than constructing new complex strings from scratch.

Common Mistakes

• Using SETRANGE on non-string keys will result in an error.
• Specifying an offset beyond the current string length may lead to unexpected results due to implicit padding with null bytes.

FAQs

What happens if the offset is larger than the current string length?

If the offset is beyond the current length of the string, Redis pads the string with null bytes up to the specified offset before adding the new value.

Can I use SETRANGE on keys holding types other than strings?

No, SETRANGE only works with keys that hold string values. Applying it to a non-string key will result in an error.