alexeykudinkin commented on a change in pull request #4739:
URL: https://github.com/apache/hudi/pull/4739#discussion_r802179203
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File path:
hudi-common/src/main/java/org/apache/hudi/metadata/HoodieMetadataPayload.java
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@@ -362,28 +361,33 @@ private HoodieMetadataColumnStats
combineColumnStatsMetadatat(HoodieMetadataPayl
return filesystemMetadata.entrySet().stream().filter(e ->
e.getValue().getIsDeleted() == isDeleted);
}
- private Map<String, HoodieMetadataFileInfo>
combineFilesystemMetadata(HoodieMetadataPayload previousRecord) {
+ private Map<String, HoodieMetadataFileInfo>
combineFileSystemMetadata(HoodieMetadataPayload previousRecord) {
Map<String, HoodieMetadataFileInfo> combinedFileInfo = new HashMap<>();
+
+ // First, add all files listed in the previous record
if (previousRecord.filesystemMetadata != null) {
combinedFileInfo.putAll(previousRecord.filesystemMetadata);
}
+ // Second, merge in the files listed in the new record
if (filesystemMetadata != null) {
- filesystemMetadata.forEach((filename, fileInfo) -> {
- // If the filename wasnt present then we carry it forward
- if (!combinedFileInfo.containsKey(filename)) {
- combinedFileInfo.put(filename, fileInfo);
- } else {
- if (fileInfo.getIsDeleted()) {
- // file deletion
- combinedFileInfo.remove(filename);
- } else {
- // file appends.
- combinedFileInfo.merge(filename, fileInfo, (oldFileInfo,
newFileInfo) -> {
- return new HoodieMetadataFileInfo(oldFileInfo.getSize() +
newFileInfo.getSize(), false);
- });
- }
- }
+ validatePayload(type, filesystemMetadata);
+
+ filesystemMetadata.forEach((key, fileInfo) -> {
+ combinedFileInfo.merge(key, fileInfo,
+ // Combine previous record w/ the new one, new records taking
precedence over
+ // the old one
+ //
+ // NOTE: That if previous listing contains the file that is being
deleted by the tombstone
+ // record (`IsDeleted` = true) in the new one, we simply
delete the file from the resulting
+ // listing as well as drop the tombstone itself.
+ // However, if file is not present in the previous record we
have to persist tombstone
+ // record in the listing to make sure we carry forward
information that this file
+ // was deleted. This special case could occur since the
merging flow is 2-stage:
+ // - First we merge records from all of the delta
log-files
+ // - Then we merge records from base-files with the delta
ones (coming as a result
+ // of the previous step)
+ (oldFileInfo, newFileInfo) -> newFileInfo.getIsDeleted() ? null :
newFileInfo);
Review comment:
You've brought up interesting point. First of all, MT updates and actual
FS changes are actually part of the `commit` operation which is atomic (as in:
it's performed under lock).
But if extend your train of thought, and assume for a moment that it could
be possible that MT updates and FS operations aren't atomic, we actually _will
not be able_ to guarantee consistency b/w actual state of the FS and MT, b/c at
any point MT operations (accompanying actual FS ops) could get re-ordered which
practically would entail that we will potentially have incorrect MT state b/c
"merge" of MT records is not a commutative operation (b/c it inherently relies
on ordering for deletes). Example of such inconsistency would be "resurrecting
file" where (in order)
1. File F is Appended (A_1)
2. File F is Deleted (D_1)
3. MT record (deleted=true) is added (for D_1)
4. MT record (size=..., deleted=false) is added (for A_1)
Therefore, we will have to provide for such atomicity (which we do)
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