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Re: Uber migrated from Postgres to MySQL

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On Wed, Jul 27, 2016 at 3:34 AM, Achilleas Mantzios <achill@xxxxxxxxxxxxxxxxxxxxx> wrote:
On 27/07/2016 10:15, Condor wrote:
On 26-07-2016 21:04, Dorian Hoxha wrote:
Many comments: https://news.ycombinator.com/item?id=12166585
https://www.reddit.com/r/programming/comments/4uph84/why_uber_engineering_switched_from_postgres_to/

On Tue, Jul 26, 2016 at 7:39 PM, Guyren Howe <guyren@xxxxxxxxx> wrote:

Honestly, I've never heard of anyone doing that. But it sounds like
they had good reasons.

https://eng.uber.com/mysql-migration/

Thoughts?

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They are right for upgrades.
It's a hard to shutdown 1 TB database and wait couple of days pg_upgrade to finish upgrade and meanwhile database is offline.
In some distros after upgrade of PG version you don't have old binary and library, need to do full dump and restore that take time and disk space.

Our last 1TB upgrade from 9.0 -> 9.3 went like a charm in something like seconds. (with the -k option)
However, be warned that the planing and testing took one full week.

That being said, it doesn't really provide a back-out plan.  The beauty of replication is that you can halt the upgrade at any point if need be and cut your (hopefully small) losses. If you use -k, you are all in.  Sure, you could setup a new standby, stop traffic, upgrade whichever node you'd like (using -k) and still have the other ready in the event of total catastrophe.  More often than not, I see DBAs and sysads lead the conversation with "well, postgres can't replicate from one version to another, so instead.... " followed by a fast-glazing of management's eyes and a desire to buy a 'commercial database'. 

All in all, Evan's blog seemed to start out decently technical, it quickly took a turn with half-truths, outdated information and, in some cases, downright fud:

 "The bug we ran into only affected certain releases of Postgres 9.2 and has been fixed for a long time now. However, we still find it worrisome that this class of bug can happen at all. A new version of Postgres could be released at any time that has a bug of this nature, and because of the way replication works, this issue has the potential to spread into all of the databases in a replication hierarchy."


ISTM that they needed a tire swing and were using a dump truck.  Hopefully they vectored somewhere in the middle and got themselves a nice sandbox.

--Scott  
 



Regards,
Hristo S.







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Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt




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Scott Mead
Sr. Architect
OpenSCG

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