Hi Jiandan,
Glad you found my write-up on this. One of the original design goals was
to *not* implement routing logic in the client. Sticky-sessions is by
far the easiest way to implement this.
There is some retry logic in the Avatica client to resubmit requests
when a server responds that it doesn't have a connection/statement
cached that the client thinks it should (e.g. the load balancer flipped
the client to a newer server). I'm still a little concerned about this
level of "smarts" :)
I don't know if there is a fancier solution that we can do in Avatica.
We could consider sharing state between Avatica servers, but I think it
is database-dependent as to whether or not you could correctly
reconstruct an iteration through a result set.
I had talked with a dev on the Apache Hive project. He suggested that
HiveServer2 just fails the query when the client is mid-query and the
server dies (which is reasonably -- servers failing should be an
infrequent operation).
On 8/8/18 8:09 PM, JD Zheng wrote:
Hi,
Our query engine is using calcite as parser/optimizer and enumerable as runtime
if needed to federate different storage engines. We are trying to enable JDBC
access to our query engine. Everything works smoothly when we only have one
calcite/avatica server.
However, JDBC calls will fail if we run multiple instances of calcite/avatica servers
behind a generic load-balancer. Given that JDBC server is not stateless, this problem
was not a surprise. I searched around and here are the two options suggested by
phoenix developers
(https://community.hortonworks.com/articles/9377/deploying-the-phoenix-query-server-in-production-e.html
<https://community.hortonworks.com/articles/9377/deploying-the-phoenix-query-server-in-production-e.html>):
1. sticky sessions: make the router to always route a client to a given server.
2. client-driven routing: implementing Avarice’s protocol which passes an
identifier to the load balancer to control how the request is routed to the
backend servers.
Before we rush into any implementation, we would really appreciate it if anyone
can share experience or thoughts regarding this issue. Thanks,
-Jiandan
