7.8 MAINMEM option

> Creating the main-memory db via xquery (declare option or pragma) did > not work: declare option db:mainmem 'true'; or (# db:mainmem true #) > Via command line it works: set mainmem true

> 2014-05-07 11:27 GMT+02:00 Christian Grün <christian.gruen at gmail.com>: >> Creating the main-memory db via xquery (declare option or pragma) did >> not work: declare option db:mainmem 'true'; or (# db:mainmem true #) >> Via command line it works: set mainmem true > Yes, this is on purpose, and for two reasons: > > * All databases that are opened within a query will eventually be closed again. > * If a main-memory database is created, it has no disk representation, > and as soon as the query is evaluated, it gets lost. > > A long time ago, BaseX started as a main-memory database, which is > actually the main reason for the MAINMEM flag. Step by step, we > reduced internal main memory dependencies, as we would have to > implemented many things twice. If I remember right, the most important > mainmem scenarios are as follows: > * In the standalone context, a main-memory database can be created > (using CREATE DB), which can then be accessed by subsequent commands. > * If a BaseX server instance is started, and if a database is created > in its context (using CREATE DB), other BaseX client instances can > access (and update) this database (using OPEN, db:open, etc.) as long > as no other database is opened/created by the server. > * By the way: main-memory database instances are also created by the > invocation of doc(...) or collection(...), if the argument is not a > database (no matter which value is set for MAINMEM). In other words: > the same internal representation is used for main-memory databases and > documents/collections generated via XQuery.

> It may be worth adding such inormation in our Wiki articles on > Databases [1]; is anyone willing to do that? ;)

> > Now back to the motivation of your question: We could think about > extending the MAINMEM option and also open existing databases in > main-memory (via OPEN or db:open) if the option is activated. This > would imply that the full-text index would be ignored (currently, no > main-memory representation of this index structure exists).

> But more > importantly, updates would have to be propagated back to disk if the > database is closed (or after every update). Currently, no code exists > to convert main-memory instances to disk (but the data structures are > at least similar),

> > Christian > > [1] http://docs.basex.org/wiki/Databases

> I guess that is the confusing part - when using create db I'd expect > the database to last until I drop it (or the server ist stoppend in this case)

> I would give it a try (account request sent)

> I am not sure what wou mean with ignoring full-text, queries with > "containing text ..." > seem to work (at least in my tests)

> I can think of supporting the development of such functionality if > you consider worth the effort

> Considering the current penalty with calling optimize() after every change > and otherwise (at least for me) no big differences in usage this would make > an interesting use case

>> Considering the current penalty with calling optimize() after every change >> and otherwise (at least for me) no big differences in usage this would make >> an interesting use case > > When it comes to optimize(), you could play around with the UPDINDEX option.

> > Christian