| Code with Finding: |
class LogMergePolicy {
/** Returns the merges necessary to optimize the index.
* This merge policy defines "optimized" to mean only one
* segment in the index, where that segment has no
* deletions pending nor separate norms, and it is in
* compound file format if the current useCompoundFile
* setting is true. This method returns multiple merges
* (mergeFactor at a time) so the {@link MergeScheduler}
* in use may make use of concurrency. */
public MergeSpecification findMergesForOptimize(SegmentInfos infos,
int maxNumSegments, Set segmentsToOptimize) throws IOException {
MergeSpecification spec;
assert maxNumSegments > 0;
if (!isOptimized(infos, maxNumSegments, segmentsToOptimize)) {
// Find the newest (rightmost) segment that needs to
// be optimized (other segments may have been flushed
// since optimize started):
int last = infos.size();
while(last > 0) {
final SegmentInfo info = infos.info(--last);
if (segmentsToOptimize.contains(info)) {
last++;
break;
}
}
if (last > 0) {
spec = new MergeSpecification();
// First, enroll all "full" merges (size
// mergeFactor) to potentially be run concurrently:
while (last - maxNumSegments + 1 >= mergeFactor) {
spec.add(new OneMerge(infos.range(last-mergeFactor, last), useCompoundFile));
last -= mergeFactor;
}
// Only if there are no full merges pending do we
// add a final partial (< mergeFactor segments) merge:
if (0 == spec.merges.size()) {
if (maxNumSegments == 1) {
// Since we must optimize down to 1 segment, the
// choice is simple:
if (last > 1 || !isOptimized(infos.info(0)))
spec.add(new OneMerge(infos.range(0, last), useCompoundFile));
} else if (last > maxNumSegments) {
// Take care to pick a partial merge that is
// least cost, but does not make the index too
// lopsided. If we always just picked the
// partial tail then we could produce a highly
// lopsided index over time:
// We must merge this many segments to leave
// maxNumSegments in the index (from when
// optimize was first kicked off):
final int finalMergeSize = last - maxNumSegments + 1;
// Consider all possible starting points:
long bestSize = 0;
int bestStart = 0;
for(int i=0;i<last-finalMergeSize+1;i++) {
long sumSize = 0;
for(int j=0;j<finalMergeSize;j++)
sumSize += size(infos.info(j+i));
if (i == 0 || (sumSize < 2*size(infos.info(i-1)) && sumSize < bestSize)) {
bestStart = i;
bestSize = sumSize;
}
}
spec.add(new OneMerge(infos.range(bestStart, bestStart+finalMergeSize), useCompoundFile));
}
}
} else
spec = null;
} else
spec = null;
return spec;
}
}
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