redis object命令

OBJECT subcommand [arguments [arguments …]]

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 ziplist or linkedlist.
    The ziplist is the special representation that is used to save space for
    small lists.
  • Sets can be encoded as intset or hashtable.
    The intset is a special encoding used for small sets composed solely of
    integers.
  • Hashes can be encoded as ziplist or hashtable.
    The ziplist is a special encoding used for small hashes.
  • Sorted Sets can be encoded as ziplist or skiplist format.
    As for the List type small sorted sets can be specially encoded using
    ziplist, while the skiplist encoding 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.

*返回值

Different return values are used for different subcommands.

  • Subcommands refcount and idletime return integers.
  • Subcommand encoding returns a bulk reply.

If the object you try to inspect is missing, a null bulk reply is returned.

*例子

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"