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71 lines
3.3 KiB
Markdown
71 lines
3.3 KiB
Markdown
kissdb
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======
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(Keep It) Simple Stupid Database
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KISSDB is about the simplest key/value store you'll ever see, anywhere.
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It's written in plain vanilla C using only the standard string and FILE
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I/O functions, and should port to just about anything with a disk or
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something that acts like one.
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It stores keys and values of fixed length in a stupid-simple file format
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based on fixed-size hash tables. If a hash collision occurrs, a new "page"
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of hash table is appended to the database. The format is append-only.
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There is no delete. Puts that replace an existing value, however, will not
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grow the file as they will overwrite the existing entry.
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Hash table size is a space/speed trade-off parameter. Larger hash tables
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will reduce collisions and speed things up a bit, at the expense of memory
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and disk space. A good size is usually about 1/2 the average number of
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entries you expect.
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Features:
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* Tiny, compiles to ~4k on an x86_64 Linux system
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* Small memory footprint (only caches hash tables)
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* Very space-efficient (on disk) if small hash tables are used
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* Makes a decent effort to be robust on power loss
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* Pretty respectably fast, especially given its simplicity
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* 64-bit, file size limit is 2^64 bytes
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* Ports to anything with a C compiler and stdlib/stdio
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* Public domain
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Limitations:
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* Fixed-size keys and values, must recreate and copy to change any init size parameter
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* Add/update only, no delete
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* Iteration is supported but key order is undefined
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* No search for subsets of keys/values
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* No indexes
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* No transactions
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* No special recovery features if a database gets corrupted
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* No built-in thread-safety (guard it with a mutex in MT code)
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* No built-in caching of data (only hash tables are cached for lookup speed)
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* No endian-awareness (currently), so big-endian DBs won't read on little-endian machines
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Alternative key/value stores and embedded databases:
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* [MDB](http://symas.com/mdb/) uses mmap() and is very fast (not quite as tiny/simple/portable)
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* [CDB](http://cr.yp.to/cdb.html) is also minimal and fast, probably the closest thing to this (but has a 4gb size limit)
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* [Kyoto Cabinet](http://fallabs.com/kyotocabinet/) is very fast, full-featured, and modern (license required for commercial use)
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* [SQLite](http://www.sqlite.org/) gives you a complete embedded SQL server (public domain, very mature, much larger)
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* Others include GDBM, NDBM, Berkeley DB, etc. Use your Googles. :)
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KISSDB is good if you want space-efficient relatively fast write-once/read-many storage
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of keys mapped to values. It's not a good choice if you need searches, indexes, delete,
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structured storage, or widely varying key/value sizes. It's also probably not a good
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choice if you need a long-lived database for critical data, since it lacks recovery
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features and is brittle if its internals are modified. It would be better for a cache
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of data that can be restored or "re-learned," such as keys, Bitcoin transactions, nodes
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on a peer-to-peer network, log analysis results, rendered web pages, session cookies,
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auth tokens, etc.
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KISSDB is in the public domain. One reason it was written was the
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poverty of simple key/value databases with wide open licensing. Even old
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ones like GDBM have GPL, not LGPL, licenses.
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See comments in kissdb.h for documentation. Makefile can be used to build
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a test program on systems with gcc.
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Author: Adam Ierymenko / ZeroTier Networks LLC
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