mikemccand commented on code in PR #14893:
URL: https://github.com/apache/lucene/pull/14893#discussion_r2187552058
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lucene/core/src/java/org/apache/lucene/index/TieredMergePolicy.java:
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@@ -130,7 +130,7 @@ public double getMaxMergedSegmentMB() {
/**
* Sets the maximum percentage of doc id space taken by deleted docs. The
denominator includes
* both active and deleted documents. Lower values make the index more space
efficient at the
- * expense of increased CPU and I/O activity. Values must be between 5 and
50. Default value is
+ * expense of increased CPU and I/O activity. Values must be between 0 and
50. Default value is
Review Comment:
Can we enhance this javadoc to note the dangers of very low (< 5%) target
deletions? Something like:
```
Values below 5% can lead to exceptionally high merge cost where indexing
will continuously
merge nearly all segments, and select newly merged segments immediately for
merging again,
often forcing degenerate merge selection like singleton merges. If you
venture into this dark
forest, consider limiting the maximum number of concurrent merges and
threads (link to
ConcurrentMergeScheduler's setMaxMergesAndThreads) as a coarse attempt to
bound the
otherwise pathological indexing behavior.
```
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