[BUG] Lower the log level from WARN to DEBUG for experimental feature: "batch allocation of unassigned shards" #18137
Description
Describe the bug
The ticket #14744 already pointed out that there is an experimental feature that if not enabled produces log message as WARN level.
If the feature is not enabled then log contains the following WARN messages:
Falling back to single shard assignment since batch mode disable or multiple custom allocators set
While the discussion in #14744 indicates that it should be "safe" to enable this feature it is still pointed out that [sic] "we want it to bake it for some time before turning the default to true to ensure no regressions at all".
As of writing the feature is probably still in experimental mode and the logging still at the WARN level.
This is causing an unnecessary pollution in our logging store as there is really nothing our OPS can do to address this WARN message. We do not feel confident turning this experimental feature on while officially it hasn't been confirmed in upstream yet. To get rid of this logging message we would need to modify log4j2 configuration and probably introduce a StringMatchFilter to filter this particular message out. Currently, we are just patching upstream code and we do change the logging level to DEBUG.
My proposal/ask is to lower the log level from WARN to DEBUG in upstream.
I am happy to send PR.
Related component
Cluster Manager
To Reproduce
- Go to opensearch log files and search for "Falling back to single shard assignment since batch mode disable or multiple custom allocators set"
Expected behavior
No WARN log messages should be produced for features that require experimental features to be turned on. OPS maintaining production clusters should not be bothered by future features that are still in experimental mode.
Additional Details
Plugins
n/a
Screenshots
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Host/Environment (please complete the following information):
- Version [2.14.1] and above
Additional context
n/a