nessDB is an embedded key-value DBMS written in ANSI C with BSD license. It does not require any external dependencies and works in most POSIX systems. As for storage engine, nessDB used LSM-tree (Log-Structured Merge Tree) in v1.8, B-epsilon-tree in v2.0, and will use fractal-tree in v3.0. nessDB also used fractional cascading to speed up query.
It has released two main versions (v1.8 and v2.0), while v3.0 is still work in progress.
It does not fully support no redo log and recovery. nessDB v3.0 will support sharp checkpoint with a 60 seconds period according to the code, but the recovery part has not been finished.
nessDB v3.0 used **Snappy**, a data compression and decompression library written in C++ by Google, to compress the buffered-tree node data when serializing the node to disk and decompress it when deserializing. nessDB v2.0 used **QuickLZ**, a compression library written in C, to compress the key-value pair.
nessDB v3.0 will use two-phase locking with deadlock detection, but this part does not finish yet. For deadlock detection, nessDB v3.0 will use **Helgrind**, a thread error detector that can detect potential deadlocks arising from lock ordering problems. For nessDB v2.0, it is a single-thread engine. The engine can process a single request at a time.
nessDB is a key-value DBMS, which supports Redis-like protocol, such as SET, GET, DEL, EXISTS. To be specific, both key and value are general raw data and are represented by a pointer with length.
nessDB is a key-value DBMS so it does not support foreign key.
nessDB used LSM-tree (Log-Structured Merge Tree) in v1.8, Small-Splittable Tree in v2.0, and will use fractal-tree in v3.0 for key-value storage. Those data structures are suitable for high-performance insertion compared to B-tree.
nessDB v3.0 support four isolation levels: read uncommitted, read committed, repeatable read and serializable.
nessDB does not support join. It is a key-value DBMS with only interfaces such as SET, GET, DEL, EXISTS.
nessDB is a key-value DBMS and each query only involves a single key-value pair.
nessDB is an embedded DBMS with custom C API, as well as wrappers for Java, Python and Lua.
nessDB is a disk-oriented DBMS. All data are stored in nonvalatile storage after shutdown.
nessDB v2.0 used a Small-Splittable Tree (SST), a variant of B-Epsilon-tree, for storage engine. SST has multiple levels with exponential expanding size. For level0, the data is un-sorted and the other levels are sorted. This data structure has good performance for random write.
For a tree node file, there is a header which stored the key-value pair in each level. And the header is followed by several var-length key-value pairs with data-offset.
C, C++, Java, Lua, Python