kfaraz opened a new pull request, #14269:
URL: https://github.com/apache/druid/pull/14269
## Changes
The defaults of the following config values in the
`CoordinatorDynamicConfig` are being updated.
#### 1. `maxSegmentsInNodeLoadingQueue = 500` (previous = 100)
Rationale: With round-robin segment assignment now being the default
assignment technique, the Coordinator can assign a large number of
under-replicated/unavailable segments very quickly. Before round-robin, a large
queue size would cause the Coordinato to get stuck in `RunRules` duty due to
very slow strategy-based cost computations.
#### 2. `replicationThrottleLimit = 500` (previous = 10)
Rationale: Along with the reasoning given for
`maxSegmentsInNodeLoadingQueue`, a very low `replicationThrottleLimit` can
cause clusters to be very slow in getting to full replication, even when there
are loading threads sitting idle.
Note: It is okay to keep this value equal to
`maxSegmentsInNodeLoadingQueue`. Even with equal values, load queues will not
get filled up with just replicas, and segments that are completely unavailable
will still get a fair chance. This is because while MSINLQ applies to a single
server, `replicationThrottleLimit` applies to each tier.
#### 3. `maxSegmentsToMove = 100` (previous = 5)
Rationale: A very low value of this config (say 5) turns out to be very
ineffective in balancing especially if there are a large number of segments in
a cluster and/or a large skew between usages of two historical servers.
On the other hand, a very large value can cause excessive moves every
minute, which might have the following disadvantages:
- Load of moving segments competing with load of
unavailable/under-replicated segments
- Unnecessary network costs due to constant download and delete of segments
These defaults will be revisited after #13197 is merged.
## Testing
These values have been tried on different production cluster sizes, and have
been found to give satisfactory results.
#### Release note
Update default values of the following coordinator dynamic configs:
- `maxSegmentsInNodeLoadingQueue = 500`
- `maxSegmentsToMove = 100`
- `replicationThrottleLimit = 500`
<hr>
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