jon-wei commented on a change in pull request #11398:
URL: https://github.com/apache/druid/pull/11398#discussion_r668265782
##########
File path:
server/src/main/java/org/apache/druid/segment/loading/SegmentLoader.java
##########
@@ -29,10 +30,45 @@
* Loading segments from deep storage to local storage.
* Implementations must be thread-safe.
*/
+@UnstableApi
public interface SegmentLoader
{
boolean isSegmentLoaded(DataSegment segment);
- Segment getSegment(DataSegment segment, boolean lazy,
SegmentLazyLoadFailCallback loadFailed) throws SegmentLoadingException;
+
+ /**
+ * Returns a {@link ReferenceCountingSegment} that will be added by the
{@link org.apache.druid.server.SegmentManager}
+ * to the {@link org.apache.druid.timeline.VersionedIntervalTimeline}. This
method can be called multiple times
+ * by the {@link org.apache.druid.server.SegmentManager}
+ *
+ * Returning a {@code ReferenceCountingSegment} will let custom
implementations keep track of reference count for
+ * segments that the custom implementations are creating. That way, custom
implementations can know when the segment
+ * is in use or not.
+ * @param segment - {@link DataSegment} segment to download
+ * @param lazy - whether the loading is lazy
+ * @param loadFailed - Callback to invoke if the loading fails
+ * @return Segment object wrapped inside {@link ReferenceCountingSegment}.
+ * @throws SegmentLoadingException
+ */
+ ReferenceCountingSegment getSegment(DataSegment segment, boolean lazy,
SegmentLazyLoadFailCallback loadFailed) throws SegmentLoadingException;
Review comment:
Is the SegmentLoader guaranteed to return the same
ReferenceCountingSegment instance across multiple calls of getSegment? Should
it?
##########
File path:
server/src/main/java/org/apache/druid/segment/loading/SegmentLoaderLocalCacheManager.java
##########
@@ -237,44 +249,83 @@ public File getSegmentFiles(DataSegment segment) throws
SegmentLoadingException
}
/**
- * location may fail because of IO failure, most likely in two cases:<p>
+ * If we have already reserved a location before, probably via {@link
#reserve(DataSegment)}, then only that location
+ * should be tried. Otherwise, we would fetch locations using {@link
StorageLocationSelectorStrategy} and try all
+ * of them one by one till there is success.
+ * Location may fail because of IO failure, most likely in two cases:<p>
* 1. druid don't have the write access to this location, most likely the
administrator doesn't config it correctly<p>
* 2. disk failure, druid can't read/write to this disk anymore
- *
+ * <p>
* Locations are fetched using {@link StorageLocationSelectorStrategy}.
*/
- private StorageLocation loadSegmentWithRetry(DataSegment segment, String
storageDirStr) throws SegmentLoadingException
+ private File loadSegmentWithRetry(DataSegment segment) throws
SegmentLoadingException
{
- Iterator<StorageLocation> locationsIterator = strategy.getLocations();
+ String segmentDir = getSegmentDir(segment);
+
+ // Try the already reserved location. If location has been reserved
outside, then we do not release the location
+ // here and simply delete any downloaded files. That is, we revert
anything we do in this function and nothing else.
+ for (StorageLocation loc : locations) {
+ if (loc.isReserved(segmentDir)) {
+ File storageDir = loc.segmentDirectoryAsFile(segmentDir);
+ boolean success = loadInLocationWithStartMarkerQuietly(loc, segment,
storageDir, false);
+ if (!success) {
+ throw new SegmentLoadingException("Failed to load segment %s in
reserved location [%s]", segment.getId(), loc.getPath().getAbsolutePath());
Review comment:
Should this alert and cleanup instead of failing with an exception?
##########
File path:
server/src/main/java/org/apache/druid/segment/loading/StorageLocation.java
##########
@@ -154,7 +166,8 @@ public synchronized File reserve(String
segmentFilePathToAdd, String segmentId,
{
final File segmentFileToAdd = new File(path, segmentFilePathToAdd);
if (files.contains(segmentFileToAdd)) {
- return null;
+ //TODO: is this change ok?
+ return segmentFileToAdd;
Review comment:
What's the reasoning for this change?
##########
File path:
server/src/main/java/org/apache/druid/segment/loading/SegmentLoader.java
##########
@@ -29,10 +30,45 @@
* Loading segments from deep storage to local storage.
* Implementations must be thread-safe.
*/
+@UnstableApi
public interface SegmentLoader
{
boolean isSegmentLoaded(DataSegment segment);
- Segment getSegment(DataSegment segment, boolean lazy,
SegmentLazyLoadFailCallback loadFailed) throws SegmentLoadingException;
+
+ /**
+ * Returns a {@link ReferenceCountingSegment} that will be added by the
{@link org.apache.druid.server.SegmentManager}
+ * to the {@link org.apache.druid.timeline.VersionedIntervalTimeline}. This
method can be called multiple times
+ * by the {@link org.apache.druid.server.SegmentManager}
+ *
+ * Returning a {@code ReferenceCountingSegment} will let custom
implementations keep track of reference count for
+ * segments that the custom implementations are creating. That way, custom
implementations can know when the segment
+ * is in use or not.
+ * @param segment - {@link DataSegment} segment to download
+ * @param lazy - whether the loading is lazy
+ * @param loadFailed - Callback to invoke if the loading fails
+ * @return Segment object wrapped inside {@link ReferenceCountingSegment}.
+ * @throws SegmentLoadingException
+ */
+ ReferenceCountingSegment getSegment(DataSegment segment, boolean lazy,
SegmentLazyLoadFailCallback loadFailed) throws SegmentLoadingException;
+
File getSegmentFiles(DataSegment segment) throws SegmentLoadingException;
+
+ /**
+ * Tries to reserve the space for a segment on any location. We only return
a boolean result instead of a pointer to
+ * {@link StorageLocation} since we don't want callers to operate on {@code
StorageLocation} directly outside {@code SegmentLoader}.
+ * {@link SegmentLoader} operates on the {@code StorageLocation} objects in
a thread-safe manner.
+ *
+ * @param segment - Segment to reserve
+ * @return True if enough space found to store the segment, false otherwise
+ */
+ boolean reserve(DataSegment segment);
+
+ /**
+ * Reverts the effects of {@link #reserve(DataSegment)} (DataSegment)} by
releasing the location reserved for this segment.
+ * @param segment - Segment to release the location for.
+ * @return - True if any location was reserved and released, false otherwise.
+ */
+ boolean release(DataSegment segment);
Review comment:
What calls `release()`?
##########
File path:
server/src/main/java/org/apache/druid/segment/loading/SegmentLoaderLocalCacheManager.java
##########
@@ -203,8 +219,8 @@ public Segment getSegment(DataSegment segment, boolean
lazy, SegmentLazyLoadFail
} else {
factory = new MMappedQueryableSegmentizerFactory(indexIO);
}
-
- return factory.factorize(segment, segmentFiles, lazy, loadFailed);
+ Segment baseSegment = factory.factorize(segment, segmentFiles, lazy,
loadFailed);
+ return ReferenceCountingSegment.wrapSegment(baseSegment,
segment.getShardSpec());
Review comment:
Since it's a stateful object with a reference count, it seems a little
weird to me that each call is returning a new instance (which would have a
fresh reference state)
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