Database Reference
In-Depth Information
# Replication
role:master
connected_slaves:0
# CPU
used_cpu_sys:69.16
used_cpu_user:35.95
used_cpu_sys_children:0.00
used_cpu_user_children:0.00
# Keyspace
> db0:keys=1,expires=0,avg_ttl=0
The preceding output shows the results of the
info
command. Some of the
output has been omitted to save space, but there are some items of interest
that become useful when administering and monitoring a Redis instance.
Because Redis is a key-value store, the most basic commands are for setting
keys. Keys in the Redis world are generally considered to be string values,
even when they are being used to represent integer or floating-point values.
To set or get a key, use the
SET <key> <value>
and
GET <key>
commands, respectively. If there are several keys to be set or retrieved in
a single call, then you can use the
MSET <key1> <value1> <key2>
<value2>
and
MGET <key1> <key2>
commands instead of issuing
multiple calls. In all cases, if a key does not exist the
GET
command and
its variants return a
NULL
value. If only an existence check is required, the
EXISTS
command is also available. The existence command is usually used
in concert with Redis' scripting functionality, which is discussed later.
The next-most-complicated data structure in Redis is the hash table. This
form of key allows for the storage of subkeys similar to the
Map
collection
in Java or a Dictionary type in other languages such as JavaScript. Instead
of the simple
GET
and
SET
commands, you use
HSET <key> <subkey>
<value>
and
HGET <key> <subkey>
to access elements of the hash table
with
HMSET
and
HMGET
allowing for updates or retrieval of multiple subkeys
from a hash table. To retrieve all subkeys and their values, use
HGETALL
with
HKEYS
and
HVALUES
retrieving all subkey names or subkey values
respectively.
Both normal keys and hash tables support atomic counters. For normal
keys, the
INCR
and
INCRBY
commands increment the value of the key by
