FrankChen021 commented on code in PR #20338:
URL: https://github.com/apache/druid/pull/20338#discussion_r4111353636
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server/src/main/java/org/apache/druid/segment/loading/SegmentLocalCacheManager.java:
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@@ -370,6 +389,101 @@ private void addFilesToCachedSegments(
}
}
+ /**
+ * Rewrite a complete on-disk cache layout for {@code segment} as a partial
(bundle) layout, returning whether it
+ * did. Called from {@link #getCachedSegments}, which runs before anything
is reserved, mounted, or serving, so
+ * there is no live entry to unmap and no cache key to swap. This method
should never be called on a 'live' entry.
+ * <p>
+ * The conversion reads the local complete file as if it were deep storage,
via a
+ * {@link DirectoryBackedRangeReader}, and materializes the bundle layout
from it. Nothing is fetched remotely.
+ * Deep storage is still probed for range-readability, because a partial
entry that cannot range-read deep storage
+ * could never fetch a bundle it is missing later, and {@link
#reservePartialForBootstrap} reclaims such a layout
+ * on the next boot anyway.
+ * <p>
+ * Transient disk cost is one segment: the complete file has to stay
readable until the bundles are written. If
+ * anything fails, the complete layout is left exactly as it was and the
segment loads the old way, so a location
+ * without the headroom degrades instead of breaking. Staging happens under
{@link #CONVERT_PATH}, swept at
+ * startup, so a crash leaves garbage rather than a half-converted segment
directory. The one lossy window is a
+ * crash between removing the complete layout and moving the converted one
into place, which costs a re-download
+ * of that segment.
+ */
+ private boolean convertCompleteLayoutToPartial(final DataSegment segment,
final StorageLocation location)
+ {
+ if (!config.isVirtualStorage() ||
!config.isVirtualStoragePartialDownloadsEnabled()) {
+ return false;
+ }
+ final File completeDir = new File(location.getPath(),
segment.getId().toString());
+ if (!new File(completeDir, IndexIO.V10_FILE_NAME).exists()) {
+ // Only a V10 segment file can be re-sliced into bundles.
+ return false;
+ }
+ try {
+ if (tryOpenRangeReader(segment) == null) {
+ return false;
+ }
+ }
+ catch (Exception e) {
+ log.warn(
+ e,
+ "Failed to open a range reader for segment[%s]; leaving its complete
cache layout alone",
+ segment.getId()
+ );
+ return false;
+ }
+
+ final File stagingDir = new File(new File(location.getPath(),
CONVERT_PATH), segment.getId().toString());
+ boolean completeLayoutRemoved = false;
+ try {
+ if (stagingDir.exists()) {
+ FileUtils.deleteDirectory(stagingDir);
+ }
+ try (PartialSegmentFileMapperV10 mapper =
PartialSegmentFileMapperV10.create(
+ new DirectoryBackedRangeReader(completeDir),
+ jsonMapper,
+ stagingDir,
+ IndexIO.V10_FILE_NAME,
+ List.of(),
+ PartialSegmentDownloadListener.NOOP,
+ config.getVirtualStorageCoalesceGapBytes(),
+ config.getVirtualStorageMaxFetchRunBytes()
+ )) {
+ mapper.ensureAllDownloaded();
+ }
+ atomicMoveAndDeleteCacheEntryDirectory(completeDir);
+ completeLayoutRemoved = true;
+ Files.move(stagingDir.toPath(), completeDir.toPath(),
StandardCopyOption.ATOMIC_MOVE);
Review Comment:
This is a real compatibility issue. `IndexMergerV10` writes a non-null
custom `SegmentizerFactory` to `factory.json`, and
`CompleteSegmentCacheEntry.mount` reads that file when restoring a complete
layout. The converted staging directory contains only the partial mapper's
header and container files; after restart, the partial path builds
`PartialQueryableIndexSegment` and never reads `factory.json`. A
broadcast-joinable factory can therefore lose its `IndexedTable` behavior after
this config switch. Please preserve/exclude custom factories as suggested.
<!-- mergelens:review -->
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