Interacting with Databases presents information about databases relative to Tcl .
TDBC is the official specification for and implementation of a generic database interface. The focus now is on expanding the number drivers to cover more databases. Older database interface packages are being modified or rewritten as TDBC drivers.
Jacob Levy has written the Interfaces to lesser known databases such as OBST, Coral, MOREplus, Qddb, etc.
AOLserver has its own drivers for many databases (Oracle, PostgreSQL, Sybase, Solid, etc.), all accessible from the same ns_db Tcl API. And the AOL maintainers have started refactoring the C code to make some of this stuff shared libraries, and thus potentially very useful in non-AOLserver environments as well...
The Redis project [L1 ] supports Tcl as well as other languages. The home page says of Redis:
Redis is an advanced key-value store. It is similar to memcached but the dataset is not volatile, and values can be strings, exactly like in memcached, but also lists, sets, and ordered sets. All this data types can be manipulated with atomic operations to push/pop elements, add/remove elements, perform server side union, intersection, difference between sets, and so forth. Redis supports different kind of sorting abilities.
In order to be very fast but at the same time persistent the whole dataset is taken in memory, and from time to time saved on disc asynchronously (semi persistent mode) or alternatively every change is written into an append only file (fully persistent mode). Redis is able to rebuild the append only file in background when it gets too big.
The Redis source tree contains test scripts written in Tcl.