On 21/02/12 05:00, Holger Knublauch wrote:
I guess many Jena users have run into the issue that you cannot write
to a memory graph if any query iterators are open (or rather: the
iterators throw an exception as soon as a write happens).
Are there any strong technical obstacles that make it impossible to
implement a Jena Graph that doesn't have this limitation? What are
the trade-offs? Does anyone know of an in-memory RDF store in Java
that allows concurrent writes? This could then be plugged behind
Jena's Graph interface.
No.
Space. Implementation costs.
Yes.
(what semantics do you want for the query? It does or does not see
changes as it goes along?)
The Graph API is an abstraction that can be implemented with different
non-functional characteristics.
If you want write-while-read AND consistency either behind the scenes do
what you have to do to avoid concurrency (e.g. have a grah and a record
of adds and deletes). Or use a transactional system and use two
transactions ...
TDB runs in-memory as well as disk. It's not designed for performance
but all that means is that it's never been tested for such. Every thing
works - the test suite uses an in-memory dataset where possible because
disk-based is very, very slow.
(if you don't want consistency just use concurrent hash maps for indexes
- but if you have > 1 index, they may not be consistent)
Andy
Thanks Holger
