SSDB is originally an individual open-source project. It was started by Zuyang Wu in 2013, aiming to work as an alternative for Redis. Currently, SSDB is being used in many productive environments to replace Redis, including several well-known companies and startups.
SSDB does not support concurrency control, because operations are executed individually and there is no transaction. However, unlike Redis, SSDB supports multi-threads to avoid write operations blocking read operations (since 1.5.2). All write operations are executed in a single thread while read operations are executed in other threads.
SSDB supports logical logging for its operations. It has multiple logging levels, including fatal, error, warn, info, debug(recommended), trace. The log file will change its name and create a new log file when exceeding the size limitation.
SSDB is a NoSQL database, and join operations are not supported.
SSDB uses LevelDB as its storage engine. Operations on different data types are based on the implementation of LevelDB. LevelDB uses Log-Structured Merge Tree for data storage, and Skip List for memtable.
SSDB supports four main data types, which are key-value, hashmap, sorted set and list. The key-value data type is used to store data with no strong relations. The hashmap is used to store data in different set with counting and sorting based on key value. Sorted set sorts all entries based on a score integer, and unlike key-value and hashmap, it cannot be used to store large data. List stores data in the queue structure.
No query compilation is found in SSDB.
SSDB supports Snappy data compression library developed by Google since version 1.6.2. In LevelDB, developers should explicitly set parameters to use Snappy in the compile time. SSDB changes this feature by directly integrating the source code of Snappy to the project. By default, SSDB will use Snappy, but users can still choose to use a non-compression version. SSDB with Snappy compression is compatible with non-compression data.
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