Rob Vesse created JENA-648:
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Summary: Make TDB datasets harder to corrupt
Key: JENA-648
URL: https://issues.apache.org/jira/browse/JENA-648
Project: Apache Jena
Issue Type: Improvement
Components: TDB
Reporter: Rob Vesse
This RFE comes out of discussions I had in person with Andy earlier this week.
On the mailing lists and Q&A sites we see a steady stream of questions from
people who have corrupted TDB databases and it would be nice if we could put in
place features that make this harder to do.
There are two main things we should do in the long term as I see it:
# Make using TDB non-transactonally more difficult
# Put in place some mechanism to make it difficult for multiple JVMs to access
the same TDB dataset simultaneously
Me and Andy think the first could be achieved by making TDB datasets operation
in auto-commit more rather than non-transactional mode by default. In order to
allow this we likely need upgradeable read transactions to be supported. As
part of this change non-transactional mode would still be supported but users
would have to explicitly set some "Here be Dragons" style flag in order to do
this. Users who aren't using transactions currently would likely merely see
performance drop since suddenly they are getting auto-commits on every
operation but when they complain we can tell them they should be using
transactions properly to ensure their TDB databases remain uncorrupted.
As far as the second point goes we could likely do this the way a lot of other
applications do by having the code write a lock file to disk when a database is
opened which contains the owning processes PID. Whenever you go to open a
database the presence of the lock file is checked for and if present the PID
validated with the code refusing to open the database if the PIDs do not match.
There would likely need to be some code to cope with the case where the lock
file gets left around and the owning PID is not alive but that shouldn't be too
complicated.
Since these may be considered as substantial behavioural changes to TDB these
may likely go into Jena 3
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