jacek-lewandowski commented on code in PR #2713:
URL: https://github.com/apache/cassandra/pull/2713#discussion_r1336214126
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src/java/org/apache/cassandra/cql3/statements/DescribeStatement.java:
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@@ -132,8 +132,13 @@ public final ResultMessage execute(QueryState state,
QueryOptions options, long
@Override
public ResultMessage executeLocally(QueryState state, QueryOptions options)
{
- Keyspaces keyspaces = Schema.instance.distributedAndLocalKeyspaces();
- UUID schemaVersion = Schema.instance.getVersion();
+ UUID schemaVersion;
+ Keyspaces keyspaces;
+ do
+ {
+ schemaVersion = Schema.instance.getVersion();
Review Comment:
The error was not coming from this place - this is a bug I discovered while
inspecting the code. Although the update of version and list of keyspaces is
synchronized, they are not updated atomically. In particular, while the list of
keyspaces is updated incrementally with each added/modified/dropped keyspace,
the version is updated at the of the entire schema transformation. It is
because we do not know the intermediate schema versions, and also for the
performance reasons.
Therefore, this simple loop ensures that the schema did not change while we
requested list of keyspaces. In other words, schema version and the keyspaces
match.
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