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MSET

Introduction​

In Dragonfly, as well as in Redis and Valkey, the MSET command is used to set multiple key-value pairs atomically in a single operation. This means that either all the keys are set or none of them are, ensuring consistency across a set of operations.

The MSET command is a more efficient way to set multiple keys when compared to multiple calls to SET, as it minimizes the number of requests made to the database.

Syntax​

MSET key value [key value ...]
  • Time complexity: O(N) where N is the number of keys to set.
  • ACL categories: @write, @string, @slow

Parameter Explanations​

  • key: The key to be set.
  • value: The value to associate with the key.
  • You can input multiple key-value pairs by repeating this [key value] pattern.

Return Values​

The MSET command always returns OK regardless of whether the keys already exist or not. It will overwrite any existing keys with the provided values.

Code Examples​

Basic Example​

Set multiple key-value pairs:

dragonfly> MSET key1 "value1" key2 "value2" key3 "value3"
OK
dragonfly> GET key1
"value1"
dragonfly> GET key2
"value2"
dragonfly> GET key3
"value3"

Overwriting Existing Keys​

If any of the specified keys already exist, MSET will overwrite them:

dragonfly> SET key1 "initial"
OK
dragonfly> MSET key1 "new_value" key2 "additional_value"
OK
dragonfly> GET key1
"new_value"
dragonfly> GET key2
"additional_value"

Atomic Operations with MSET​

The atomic nature of the MSET command ensures that all keys are set together, providing consistency across values even in concurrent situations:

dragonfly> MSET key1 "first_value" key2 "second_value" key3 "third_value"
OK

# Atomicity ensures these values are set together.
dragonfly> MGET key1 key2 key3
1) "first_value"
2) "second_value"
3) "third_value"

Best Practices​

  • Use MSET when you need to update multiple keys at once, as it's more efficient than separate SET commands.
  • Since MSET performs overwrite operations, ensure that overwriting values is intended in your use case.

Common Mistakes​

  • Mixing up key-value pairs: Ensure that the number of arguments passed to MSET is even (each key must have a corresponding value).
  • Assuming MSET will fail if any of the keys already exist; in fact, it does not check whether a key exists and will always overwrite the value.

FAQs​

What happens if one of the keys already exists?​

MSET will overwrite any existing key. It does not perform checks for existing values and does not provide a conditional setting mechanism.

Can I use MSET without arguments?​

No, you must provide at least one key-value pair. If the total number of arguments is not even, you will get a syntax error.

How does MSET differ from SET?​

While SET sets a single key-value pair, MSET allows you to set multiple key-value pairs in one atomic operation, which can be more efficient in batch updates. On the other hand, SET provides more options, such as NX, EX, and so forth, for more versatile operations on that single key.