clintropolis commented on a change in pull request #8106: fix npe with sql
metadata manager polling and empty database
URL: https://github.com/apache/incubator-druid/pull/8106#discussion_r305277531
##########
File path:
server/src/main/java/org/apache/druid/metadata/SQLMetadataSegmentManager.java
##########
@@ -967,10 +961,18 @@ public DataSegment map(int index, ResultSet r,
StatementContext ctx) throws SQLE
// segment mark calls in rapid succession. So the snapshot update is not
done outside of database poll at this time.
// Updates outside of database polls were primarily for the user
experience, so users would immediately see the
// effect of a segment mark call reflected in MetadataResource API calls.
- dataSourcesSnapshot = DataSourcesSnapshot.fromUsedSegments(
- Iterables.filter(segments, Objects::nonNull), // Filter corrupted
entries (see above in this method).
- dataSourceProperties
- );
+
+ ImmutableMap<String, String> dataSourceProperties =
createDefaultDataSourceProperties();
+ if (segments == null || segments.isEmpty()) {
+ log.info("No segments found in the database!");
+ dataSourcesSnapshot =
DataSourcesSnapshot.fromUsedSegments(Collections.emptyList(),
dataSourceProperties);
Review comment:
Yea, I was not able to observe `segments` being `null` in my experiments,
which mostly consisted of killing and restarting the mysql i was testing
against. It doesn't look like it _should_ be able to be null, the javadoc for
the `Query.list` method
```
* Executes the select
* <p/>
* Will eagerly load all results
*
* @throws org.skife.jdbi.v2.exceptions.UnableToCreateStatementException
* if there is an error creating the statement
* @throws org.skife.jdbi.v2.exceptions.UnableToExecuteStatementException
* if there is an error executing the
statement
* @throws org.skife.jdbi.v2.exceptions.ResultSetException if there is
an error dealing with the result set
```
makes it look like it's either going to make a list or throw an exception.
If we are confident it shouldn't happen then it should just be removed i
think, but if still unsure it might make more sense to handle `segments ==
null` separate and log and probably not update the snapshot even if it's still
null, because it's an unexpected condition that doesn't necessarily mean the
same thing as a truly empty segments table. Thoughts?
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