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A comment on Things I wished more developers knew about databases.

Re:Things I wished more developers knew about databases by AtlasBarfed on Wednesday April 22, 2020 @09:36AM (#22945368)
One thing I've noticed that in the medium term of a software service (2-5 years) is that your software should have the ability to do double-writes to and flip reads between two different datastores.

That will afford migration with as close to transparent migration with as reduced a downtime or no downtime.

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Re:Things I wished more developers knew about databases by earhart on Wednesday April 22, 2020 @10:55AM (#22946174)
That gets tricky if one of the writes fails.
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Re:Things I wished more developers knew about databases by hobs on Wednesday April 22, 2020 @10:59AM (#22946246)
Generally you get two phase commit involved here, or an asynch mirror that you can restore over if there's failure.
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Re:Things I wished more developers knew about databases by smilliken on Wednesday April 22, 2020 @11:26AM (#22946548)
Two phase commit makes a promise it can't keep. CAP theorem is not amused.

It's slow, complex, a leaky abstraction, and ahould be avoided for better consistency models.

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Re:Things I wished more developers knew about databases by hobs on Wednesday April 22, 2020 @11:31AM (#22946610)
I generally couldn't agree more, but yet its the first tool in the toolbox for a lot of databases.
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Re:Things I wished more developers knew about databases by smitty1e on Wednesday April 22, 2020 @10:06AM (#22945672)
That sort of flexibility does not sound as though it would scale well as the data get big.
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Re:Things I wished more developers knew about databases by madhadron on Wednesday April 22, 2020 @10:55AM (#22946184)
Define "big." Double writing in some form is the only option for live migration and you either bolt it on later or plan for it now.
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Re:Things I wished more developers knew about databases by smitty1e on Wednesday April 22, 2020 @02:23PM (#22948600)
When the overhead of the double writing becomes substantial enough affect the architecture.
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Re:Things I wished more developers knew about databases by madhadron on Wednesday April 22, 2020 @06:52PM (#22951078)
Ah. So bigger than Facebook or Google.
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Re:Things I wished more developers knew about databases by jatone on Wednesday April 22, 2020 @05:56PM (#22950613)
wat. particularly today with logical replication this is pretty much unnecessary.
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