Re: [Prevayler-discussion] Schema Evolution
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From: Jacob K. <ho...@vi...> - 2004-04-28 02:46:00
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At 01:42 PM 4/27/2004 -0500, you wrote: >At 11:10 AM 4/24/2004 -0700, you wrote: >>All, >> >>I wonder if the following idea would solve the schema evolution >>problem, albeit in a radical fashion... >> >>Suppose that there were no snapshots and the only record of changes >>to the prevalent system was the transaction log. The object model >>would be constructed by replaying transactions. >> >>The object model could be changed at any time, and the transaction >>classes would have to be updated to work with the new object model. > >Of course, the nice thing is that this is possible today simply by not=20 >taking a snapshot. I'm not sure what would be more manageable? Actually,= =20 >one could do a combo. Take regular snapshots for faster loading, but keep= =20 >the transaction logs around >(this may not be possible because Prevayler deletes logs that have been=20 >snapshoted, I believe). I think I may have had a brain fart here. I don't think Prevayler deletes= =20 logs, so the technique of running the transaction logs upon application=20 upgrades instead of worrying about whether the serialized snapshots are=20 compatible with the new code is probably a pretty good option. Jake > When you want to update, delete the snapshot and let the transaction=20 > logs replay with the new code. Then take a snapshot again for faster=20 > loading. You can always use source control to track versions of your= code. > > >Jake > > >>The benefits may include: >>- no schema evolution problem >>- ThereCanOnlyBeOne would make more sense when applied to >>transactions as opposed to the object model >>- less possibility of not being able to recreate state when non-ECC >>ram is corrupted >>- this approach might work better with the HttPrevayler concept >> >>The drawbacks may include: >>- references to other objects within a transaction would be trickier >>- no performance improvement by simply reloading a snapshot >> - i.e. the full log would have to be replayed >>- maintenance of multiple versions of transaction may be necessary >> >>Thoughts? >>Scot >> >> >> >> >>__________________________________ >>Do you Yahoo!? >>Yahoo! Photos: High-quality 4x6 digital prints for 25=A2 >>http://photos.yahoo.com/ph/print_splash >> >> >>------------------------------------------------------- >>This SF.net email is sponsored by: The Robotic Monkeys at ThinkGeek >>For a limited time only, get FREE Ground shipping on all orders of $35 >>or more. Hurry up and shop folks, this offer expires April 30th! >>http://www.thinkgeek.com/freeshipping/?cpg=3D12297 >>_______________________________________________ >>To unsubscribe go to the end of this page:=20 >>http://lists.sourceforge.net/lists/listinfo/prevayler-discussion >>_______________________________________________ >>"Do you still use a database?" -- http://www.prevayler.org > > > >------------------------------------------------------- >This SF.net email is sponsored by: The Robotic Monkeys at ThinkGeek >For a limited time only, get FREE Ground shipping on all orders of $35 >or more. Hurry up and shop folks, this offer expires April 30th! >http://www.thinkgeek.com/freeshipping/?cpg297 >_______________________________________________ >To unsubscribe go to the end of this page:=20 >http://lists.sourceforge.net/lists/listinfo/prevayler-discussion >_______________________________________________ >"Do you still use a database?" -- http://www.prevayler.org |