JIRA: https://jira.spring.io/browse/INT-4137
Aggregators with `SequenceSizeReleaseStrategy` do not perform well with large groups
because of an O(n) linear search to reject (discard) duplicate sequences.
Change the aggregator to use a `SimpleSequenceSizeReleaseStrategy` by default, unless
`setReleasePartialSequences(true)`.
This avoids the linear search, which is not needed for most splitter -> ... -> aggregator
flows.
Log a warning if SSRS is used.
Polishing - PR Comments
* Remove `this.logger.isWarnEnabled()` since it is redundant when our log message is just string constant
890ad63584