himanshug commented on pull request #10287:
URL: https://github.com/apache/druid/pull/10287#issuecomment-732498498
slightly surprised by `~10 secs` taken up by ... (snippet from
LogUsedSegments.java)
```
public DruidCoordinatorRuntimeParams run(DruidCoordinatorRuntimeParams
params)
{
log.debug("Starting coordination. Getting used segments.");
DataSourcesSnapshot dataSourcesSnapshot =
params.getDataSourcesSnapshot();
for (DataSegment segment :
dataSourcesSnapshot.iterateAllUsedSegmentsInSnapshot()) {
if (segment.getSize() < 0) {
log.makeAlert("No size on a segment")
.addData("segment", segment)
.emit();
}
}
// Log info about all used segments
if (log.isDebugEnabled()) {
log.debug("Used Segments");
for (DataSegment dataSegment :
dataSourcesSnapshot.iterateAllUsedSegmentsInSnapshot()) {
log.debug(" %s", dataSegment);
}
}
log.info("Found [%,d] used segments.", params.getUsedSegments().size());
return params;
}
```
I am assuming DEBUG is already not enabled, so 10 secs are going in just
iterating over the segments and checking the size to print alert.
I wonder if the slowness comes from use of `Stream` to create a flat list of
segments in ...
```
public Iterable<DataSegment> iterateAllUsedSegmentsInSnapshot()
{
return () -> dataSourcesWithAllUsedSegments
.values()
.stream()
.flatMap(dataSource -> dataSource.getSegments().stream())
.iterator();
}
```
can you try to change the code to iterate over segments using simply nested
for loops in LogUsedSegments.java , e.g.
```
for (ImmutableDruidDataSource ds :
snapshot.getDataSourcesWithAllUsedSegments()) {
for (DataSegment segment : ds.getSegments()) {
......
}
}
```
and see if it still takes `~10 secs` ? I am curious because if nested
for-loops fix the perf issue then we need to fix that as `
iterateAllUsedSegmentsInSnapshot()` is used in other places as well and could
be contributing extra `~10 secs` on each of those invocations.
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