smiklosovic commented on code in PR #4100:
URL: https://github.com/apache/cassandra/pull/4100#discussion_r2073239593
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src/java/org/apache/cassandra/service/snapshot/SnapshotManager.java:
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@@ -568,18 +570,33 @@ <T> T executeTask(AbstractSnapshotTask<T> task)
private synchronized void prePopulateSnapshots(TakeSnapshotTask task)
{
Map<ColumnFamilyStore, TableSnapshot> snapshotsToCreate =
task.getSnapshotsToCreate();
- for (Map.Entry<ColumnFamilyStore, TableSnapshot> toCreateEntry :
snapshotsToCreate.entrySet())
+ Map<ColumnFamilyStore, TableSnapshot> snapshotsToOverwrite = new
HashMap<>();
Review Comment:
@frankgh
It is used, if you look closer. What we do is that
1) on 572. we do `snapshotsToCreate = task.getSnapshotsToCreate();`
2) on 592. we do `snapshotsToOverwrite.put(toCreateEntry.getKey(),
existingSnapshot);`
3) on 597. we do `snapshotsToCreate.putAll(snapshotsToOverwrite);`
What that does is that as we iterate over `toCreateEntry :
snapshotsToCreate.entrySet()` at 578 we are removing snapshots to be created by
`toCreate.remove(toCreateEntry.getValue())` which we eventually add at 599 by
`snapshots.addAll(toCreate)`.
So, `snapshots`, will contain, by this addition,_only brand new snapshots to
be created_.
However, by `snapshotsToCreate.putAll(snapshotsToOverwrite)`, we are
effectively overwriting _snapshots to be taken_ with _already existing
snapshots_.
So the result is that `task.getSnapshotsToCreate()` will contain both brand
new snapshots as well as snapshots from `snapshots` list.
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