jtuglu1 commented on code in PR #19624:
URL: https://github.com/apache/druid/pull/19624#discussion_r3493905570
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processing/src/main/java/org/apache/druid/query/QueryMetrics.java:
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@@ -329,7 +329,16 @@ default void filterBundle(FilterBundle.BundleInfo
bundleInfo)
QueryMetrics<QueryType> reportQueryBytes(long byteCount);
/**
- * Registers "segments queried count" metric.
+ * Registers the {@code query/segments/count} metric, the number of segments
touched by the query.
+ *
+ * Emitted once per query. The value's meaning depends on the emitting
process:
+ * <ul>
+ * <li>On the Broker, it is the number of segments in the planned query
distribution (a snapshot-based
+ * count that may double-count segments that moved and were
re-fetched).</li>
+ * <li>On a data node (Historical, Peon/realtime), it is the number of
segments that node actually scanned
+ * for the query.</li>
+ * </ul>
+ * The two are disambiguated by the emitting service/host, not by the metric
name.
Review Comment:
Generally metric renaming is a pain since we need to break user's metric
setups. I feel like they both are measuring the same thing for now, so we can
potentially address in a follow-up to rename the broker-side ones.
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