gianm commented on a change in pull request #4551: Fixes and improvements to
SQL metadata caching.
URL: https://github.com/apache/incubator-druid/pull/4551#discussion_r246458112
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File path: sql/src/main/java/io/druid/sql/calcite/schema/DruidSchema.java
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@@ -59,42 +58,66 @@
import io.druid.sql.calcite.view.DruidViewMacro;
import io.druid.sql.calcite.view.ViewManager;
import io.druid.timeline.DataSegment;
-import org.apache.calcite.schema.Function;
import org.apache.calcite.schema.Table;
import org.apache.calcite.schema.impl.AbstractSchema;
import org.joda.time.DateTime;
+import java.io.IOException;
+import java.util.Comparator;
import java.util.EnumSet;
-import java.util.List;
+import java.util.HashMap;
+import java.util.HashSet;
import java.util.Map;
import java.util.Set;
+import java.util.TreeMap;
+import java.util.TreeSet;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.StreamSupport;
@ManageLifecycle
public class DruidSchema extends AbstractSchema
{
+ // Newest segments first, so they override older ones.
Review comment:
The idea is that Druid allows different segments to have different column
types, and even allows the same column to have different types across different
segments. But for SQL planning and metadata reporting purposes (e.g.
INFORMATION_SCHEMA.COLUMNS) we can only report one type per column. We are
preferring later segments (based on segment interval) over earlier ones if
there's such a conflict, and achieve that by having `SEGMENT_ORDER` be an order
that puts the newest segments first, and using it to affect the iteration order
of `segmentMap.values()` in `buildDruidTable`.
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