At PGCon we agreed to have such meeting in Vienna at least. But I think we should be prepared and try to clean all our issues before. It looks like we already out of time,but probably we could meet in Hong Kong ?
Honestly, I still don't know which approach is better, we already played with XL (ported to 9.4) and identified some very strong issues with inconsistency, which scared us, especially taking into account how easy we found them. XC people have fixed them, but I'm not sure if they were fundamental and if we could construct more sophisticated tests and find more issues in XC/XL. We also a bit disappointed by Huawei position about CSN patch, we hoped to use for our XTM. FDW approach has been actively criticized by pg_shard people and that's also made me a bit suspicious. It looks like we are doomed to continue several development forks, so we decided to work on very important common project, XTM, which we hoped could be accepted by all parties and eventually committed to 9.6. Now I see we were right, unfortunately.
Distributed transaction manager should support at least three things
1. Atomic commit
2. Atomic visibility
3. Consistent snapshots (e.g. required for repeatable reads and higher isolation levels).
I have submitted patch for implementing first for FDWs. The patch adds infrastructure to be used by all FDWs including postgres_fdw. It also adds postgres_fdw code to use this infrastructure. The same can be used to achieve atomic commit in postgres_fdw based sharding. Please see if XTM can benefit from it. If there are things that are required by XTM, please post the requirements on that thread and I will work on those. You can find the latest patch at http://www.postgresql.org/message-id/CAFjFpRfANWL53+x2HdM9TCNe5pup=oPkQSSJ-KGfr-d2efj+CQ@mail.gmail.com
Again, could we organize meeting somewhere in September ? US is not good for us, but other places should be ok. I want to have an agreement at least on XTM. We still are testing various approaches, though. We could present results of our experiments and are open to discussion. It's not easy project, but it's something we could do for 9.6.
I'm very glad Bruce started this discussion in -hackers, since it's silly to me to participate in both threads :) Let's meet in September !
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
