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by t0mas88 4646 days ago
Take a look at Event Sourcing, commonly used with CQRS. The approach is indeed to store data as change-events in an event-store (which could by a SQL database or NoSQL store, that depends on your needs) and then built one or more views (separate databases, Lucene indexes, files, anything really) to service the type of requests that the application handles.

For an example of CQRS with Event Sourcing in Java: http://axonframework.org
3 comments
strictfp 4645 days ago
SQL databases also do this. They have events called 'SQL statements' which are written to a 'journal' and applied to the domain which resides in the 'tables' of the database :)
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Tuna-Fish 4645 days ago
You seem to not understand the point. SQL databases don't count because these mechanisms are not visible, and the programming model is changing data in place.

No-one really cares how DB's are implemented under the hood, we just care about the programming model. (And speed, CAP, ACID, etc...)

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strictfp 4645 days ago
I do get the point, in fact I'm building such an app right now, but my statement is still true and I find that quite amusing.
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jimbokun 4645 days ago
Given the underlying architecture of most relational databases, is it realistically possible to do "point in time queries", without requiring playing back the entire log history into a clean database up to the point in time you want? That's not going to be very efficient.

I've only seen SQL logs presented as solutions to replication and disaster recovery, not point in time functionality.

What I'm getting at, is it even possible in principle to expose part of the inner workings of some relational database systems to get this kind of capability?

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strictfp 4645 days ago
Snapshotting and log replay should be fairly straightforward, if you save all sql statements in their entirety. Snapshots would stop the world, which might pose a problem, but I presume this is no different to other event sourcing solutions. Given the concurrency of a db, I'm also not sure that there's a strict ordering of all incoming statements.

Edit: Seems like at least Oracle is already doing this: http://en.wikipedia.org/wiki/Redo_log

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twic 4645 days ago
Not only is this possible, Oracle has had exactly that feature since 2002:

http://docs.oracle.com/cd/E11882_01/appdev.112/e17125/adfns_...

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dm3 4646 days ago
There is also http://geteventstore.com/ - an immutable event database by one of the main CQRS aficionados - Greg Young. BTW, clustered HA setup has been opensourced very recently.

Really solid and fun to work with.

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strictfp 4645 days ago
And there is also the old-school http://prevayler.org/ :)
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