The OBJECT command allows to inspect the internals of Redis Objects associated with keys. It is useful for debugging or to understand if your keys are using the specially encoded data types to save space. Your application may also use the information reported by the OBJECT command to implement application level key eviction policies when using Redis as a Cache.
The OBJECT command supports multiple sub commands:
OBJECT REFCOUNT <key>returns the number of references of the value associated with the specified key. This command is mainly useful for debugging.
OBJECT ENCODING <key>returns the kind of internal representation used in order to store the value associated with a key.
OBJECT IDLETIME <key>returns the number of seconds since the object stored at the specified key is idle (not requested by read or write operations). While the value is returned in seconds the actual resolution of this timer is 10 seconds, but may vary in future implementations.
Objects can be encoded in different ways:
- Strings can be encoded as
raw(normal string encoding) or
int(strings representing integers in a 64 bit signed interval are encoded in this way in order to save space).
- Lists can be encoded as
ziplistis the special representation that is used to save space for small lists.
- Sets can be encoded as
intsetis a special encoding used for small sets composed solely of integers.
- Hashes can be encoded as
zipmapis a special encoding used for small hashes.
- Sorted Sets can be encoded as
skiplistformat. As for the List type small sorted sets can be specially encoded using
ziplist, while the
skiplistencoding is the one that works with sorted sets of any size.
All the specially encoded types are automatically converted to the general type once you perform an operation that makes it impossible for Redis to retain the space saving encoding.
Different return values are used for different subcommands.
encodingreturns a bulk reply.
If the object you try to inspect is missing, a null bulk reply is returned.
redis> lpush mylist "Hello World" (integer) 4 redis> object refcount mylist (integer) 1 redis> object encoding mylist "ziplist" redis> object idletime mylist (integer) 10
In the following example you can see how the encoding changes once Redis is no longer able to use the space saving encoding.
redis> set foo 1000 OK redis> object encoding foo "int" redis> append foo bar (integer) 7 redis> get foo "1000bar" redis> object encoding foo "raw"