yujun777 opened a new pull request, #66691:
URL: https://github.com/apache/doris/pull/66691
### What problem does this PR solve?
Issue Number: CIR-21346 (internal SelectDB JIRA; no public GitHub issue yet)
Problem Summary:
Some users query a freshness/health-check on a follower FE before every
business request. When the follower is replaying a large journal, the freshness
query result can lag and trigger business degradation.
`Config.force_forward_all_queries = true` forces all queries to the master, but
it is cluster-wide and too coarse when clients connect through a load balancer.
The existing session variable `forward_to_master` does not participate in the
ordinary SELECT forwarding decision.
This PR adds a session-level variable `force_forward_all_queries`. A query
is forwarded to the master when either `Config.force_forward_all_queries` or
the session variable is enabled, so only the freshness queries need to opt in.
### Release note
Added a session variable `force_forward_all_queries` to force queries of the
session to be forwarded to the master FE.
### Check List (For Author)
- Test:
- Unit test: `ForceForwardAllQueriesTest` (4 scenarios: session/config
on/off combinations, passed)
- Full FE build with checkstyle passed
- Behavior changed: Yes (new session variable, default off, no behavior
change when disabled)
- Does this need documentation: No
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