APPEND

If already exists and is a string, this command appends the value at the end of the string. If key does not exist it is created and set as an empty string, so will be similar to SET in this special case.

The APPEND command can be used to create a very compact representation of a list of fixed-size samples, usually referred as time series. Every time a new sample arrives we can store it using the command

• can be used in order to obtain the number of samples.
• can be used to overwrite an existing time series.

The limitation of this pattern is that we are forced into an append-only mode of operation, there is no way to cut the time series to a given size easily because Redis currently lacks a command able to trim string objects. However the space efficiency of time series stored in this way is remarkable.

An example sampling the temperature of a sensor using fixed-size strings (using a binary format is better in real implementations).