leventov commented on a change in pull request #7185: Avoid many unnecessary
materializations of collections of 'all segments in cluster' cardinality
URL: https://github.com/apache/incubator-druid/pull/7185#discussion_r264413165
##########
File path:
server/src/main/java/org/apache/druid/metadata/MetadataSegmentManager.java
##########
@@ -59,6 +60,8 @@
Collection<ImmutableDruidDataSource> getDataSources();
+ Iterable<DataSegment> iterateAllSegments();
Review comment:
Creation of the iterable is cheap, but the creation of the underlying
*iteration* is not cheap. This method discourages iterating twice on the
result, and, in fact, even storing the result in a variable, but rather
immediately consuming it, as it happens in all use cases: they look either like
```java
for (DataSegment s : iterateAllSegments()) {
..
}
```
or
```java
iterateAllSegments().forEach(s -> ...);
```
or feeded into `Iterables.transform()`, which happens in
`DruidCoordinatorSegmentInfoLoader`.
I think the prefix `iterate` reflects this sense of discouragement well.
People may feel a little uncomfortable storing an iterable returned from such
method in a variable, but the constructions above look perfectly OK.
`getIterable()` doesn't give such sense of uncomfortableness.
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