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Re: [Fedora-directory-users] multi-master limit

Enrico M. V. Fasanelli wrote:

Dear Rich,

can you explain with some numbers on that?
Not really. I don't have any exact numbers or formulae that you can plug in various parameters such as OS, RAM, CPUs, etc.

How much RAM I need per each separate thread? How many replication agreement in a server equipped with 2, 4, 8, 16 GB RAM?

How the avg. update rate influence these numbers? And the max update rate?
In general, the higher the average update rate, the harder the server is going to have to work to send out updates to all replicas. And a very high update rate for a short period of time may spike the RAM and/or CPU usage.

30 replication agreement per server is a medium value? large? huge? Too much? Out of any hardware configuration?
I don't really have a good answer for any of these questions. I do know that at some point you are going to see a drop off in performance due to thread contention. Adding more RAM and CPUs will mitigate this drop.

Thank in advance.


Rich Megginson wrote:

Also important to keep in mind is your update rate - avg. updates per minute, max. updates per minute.


In Fedora DS, replication is supplier initiated, and will update as soon as possible by default. That is, as soon as the supplier receives the change, it will send it to the consumer. There are also programmatic ways to do it, but you usually don't need to.


That means 4 is the highest number of masters we've tested
exhaustively.  The protocol supports up to 2^32-2 masters, but you will
usually hit a practical limit in the number of replication agreements. Each repl. agreement runs a separate thread, so you will usually be
constrained by resources - available RAM, processors, etc.



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