rdblue commented on code in PR #4578:
URL: https://github.com/apache/iceberg/pull/4578#discussion_r863337777
##########
core/src/main/java/org/apache/iceberg/RemoveSnapshots.java:
##########
@@ -195,6 +299,18 @@ public void commit() {
LOG.info("Committed snapshot changes");
if (cleanExpiredFiles) {
+ TableMetadata updated = ops.refresh();
+ if (updated.refs() != null) {
+ List<SnapshotRef> branches = updated.refs()
+ .values().stream().filter(SnapshotRef::isBranch)
+ .collect(Collectors.toList());
+
+ if (branches.size() > 1) {
+ throw new UnsupportedOperationException(
+ "Deleting expired files when there is more than 1 branch is
currently not supported");
+ }
Review Comment:
The problem is that we have several cases that can't be reliably cleaned up
without using the reference set. For example:
```
A - B - C
` - D
```
If A is aged off, there is no way to know that B, C, and D share all of the
files from A. So expiring B could delete files that are referenced by D but not
C.
To take care of cases like this, we need to do reference set comparison. But
rather than implementing that all at once here, we decided to fail snapshot
expiration in the short term.
However, one thing does need to be fixed: this check should happen _before_
committing the changes. If we detect that we can't reliably clean up the table,
we shouldn't drop the snapshots anyway. So this check should come first in the
commit. (@amogh-jahagirdar)
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