I have some questions about MariaDB Xpand. Not sure whether here is the right place to ask questions or not. If not, appreciate for the suggestions of where to ask.

I firstly put my questions here, let's assume the performance topology:

1. Every node of Xpand can read and write as described in white paper, but my question is does MariaDB Xpand support Multi-Master to finish the Global Transactions? There is only one global transaction manager(GTM)  or there exists multiple GTM workers at the same time?

2. What's the usage of Paxos in Xpand? If there is only one GTM at a time, it's easy to understand: Paxos is used to determine which is the leader (GTM). 

3. MPP feature of Xpand is misleading and the document is too simple to understand the internals of MPP implementation. Queries are splitted into sub query fragments and it seems that each fragment can only do every single work. So can it support Hash Join? e.g. a join fragment builds a hash table for a small table firstly and then probes the big table from the remote node?

Thanks in advance.

Hubert Zhang