All that makes sense. Do you have any concerns/benchmarks regarding
performance after migration? Have you tried migrating your data in some
POC and measure the difference in some subset of functionality?
Just to give more context. The reason I am asking is that in Candlepin,
we always have had Postgres as a datastore. Some performance challenges
that we have been facing:
* The sheer amount of data on one node makes and the amount of time
necessary to migrate when changing schema
* Transaction lock waits - which, at occasion, can stop client
requests and bring down the service
* Transaction deadlocks
With every new functionality I sometimes think about a possibility to
use some NoSQL to make it horizontally scalable. So it would be
interesting to hear that Mongo didn't deliver the performance in Pulp's
case.
On 09/13/2016 03:11 PM, Michael Hrivnak wrote:
We have a thread here about a lot of the 3.0 stack choices, although
it seems to skip past the assumption that we're moving to postgres:
https://www.redhat.com/archives/pulp-list/2016-May/msg00042.html
I can't quickly find another summary of why, so I'll describe the
highlights here:
- Pulp has highly relational data. The core use case is managing the
relationships between content and repositories. Using a relational DB
makes that a lot easier.
- A schemaless DB makes it easy to do writes, but you have to be very
careful when doing reads that the your software is prepared for
whatever data structure comes out. If you want to enforce a schema, it
has to be done in software. It's doable, but requires great care.
- Transactions!
- The HA story with mongodb is more complex than most people realize
(certainly more complex than we expected). To get real HA with data
safety, you have to do a lot of the work in your own software.
MongoDB is great at what it does and a good fit for some use cases,
but we learned that it's not the best fit for Pulp.
Michael
On Tue, Sep 13, 2016 at 3:21 AM, Filip Nguyen <[email protected]
<mailto:[email protected]>> wrote:
I heard that Pulp is switching from Mongo to Postgre. Just out of
curiosity, I would like to learn more about the reasons why you
decided to go this direction. Is there any document/email thread
about it?
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