Strings
#sidebar StringCommandsSidebar
A String value can be at max 512 Megabytes in length.
Strings are treated as integer values by the INCR commands family, in this respect the value of an intger is limited to a singed 64 bit value.
Note that the single elements contained in Redis Lists, Sets and Sorted Sets, are Redis Strings.
Redis strings are incapsualted into Redis Objects. Redis Objects use a reference counting memory management system, so a single Redis String can be shared in different places of the dataset. This means that if you happen to use the same strings many times (especially if you have object sharing turned on in the configuration file) Redis will try to use the same string object instead to allocate one new every time.
Starting from version 1.1 Redis is also able to encode in a special way strings that are actually just numbers. Instead to save the string as an array of characters Redis will save the integer value in order to use less memory. With many datasets this can reduce the memory usage of about 30% compared to Redis 1.0.
Redis String Type
Strings are the most basic Redis kind of values. Redis Strings are binary safe, this means a Redis string can contain any kind of data, for instance a JPEG image or a serialized Ruby object, and so forth.A String value can be at max 512 Megabytes in length.
Strings are treated as integer values by the INCR commands family, in this respect the value of an intger is limited to a singed 64 bit value.
Note that the single elements contained in Redis Lists, Sets and Sorted Sets, are Redis Strings.
Implementation details
Strings are implemented using a dynamic strings library calledsds.c (simple dynamic strings). This library caches the current length of the string, so to obtain the length of a Redis string is an O(1) operation (but currently there is no such STRLEN command. It will likely be added later).Redis strings are incapsualted into Redis Objects. Redis Objects use a reference counting memory management system, so a single Redis String can be shared in different places of the dataset. This means that if you happen to use the same strings many times (especially if you have object sharing turned on in the configuration file) Redis will try to use the same string object instead to allocate one new every time.
Starting from version 1.1 Redis is also able to encode in a special way strings that are actually just numbers. Instead to save the string as an array of characters Redis will save the integer value in order to use less memory. With many datasets this can reduce the memory usage of about 30% compared to Redis 1.0.