Add replication factor column to sys table

docs/querying/sql-metadata-tables.md

@@ -137,7 +137,7 @@ Segments table provides details on all Druid segments, whether they are publishe
 |dimensions|VARCHAR|JSON-serialized form of the segment dimensions|
 |metrics|VARCHAR|JSON-serialized form of the segment metrics|
 |last_compaction_state|VARCHAR|JSON-serialized form of the compaction task's config (compaction task which created this segment). May be null if segment was not created by compaction task.|
-|replication_factor|BIGINT|Total number of replicas of the segment that are required to be loaded across all historical tiers, based on the load rule that currently applies to this segment. If this value is 0, the segment is not assigned to any historical and will not be loaded. This value is -1 if load rules for the segment have not been evaluated yet or if the segment is overshadowed and will soon be marked as unused.|
+|replication_factor|BIGINT|Total number of replicas of the segment that are required to be loaded across all historical tiers, based on the load rule that currently applies to this segment. If this value is 0, the segment is not assigned to any historical and will not be loaded or is about to be unloaded if it is currently loaded. This value is -1 if load rules for the segment have not been evaluated yet.|
 
 For example, to retrieve all currently active segments for datasource "wikipedia", use the query:
 

server/src/main/java/org/apache/druid/server/http/MetadataResource.java

@@ -189,13 +189,22 @@ private Response getAllUsedSegmentsWithAdditionalDetails(
     final Set<DataSegment> overshadowedSegments = dataSourcesSnapshot.getOvershadowedSegments();
 
     final Stream<SegmentStatusInCluster> segmentStatus = usedSegments
-        .map(segment ->
-                 new SegmentStatusInCluster(
-                     segment,
-                     overshadowedSegments.contains(segment),
-                     coordinator.getReplicationFactorForSegment(segment.getId())
-                 )
-        );
+        .map(segment -> {
+          boolean isOvershadowed = overshadowedSegments.contains(segment);
+          Integer replicationFactor;
+          if (isOvershadowed) {
+            // If the segment is overshadowed, the replication factor won't be present in the coordinator, but we know
+            // that it should be 0 as we will unload it soon.
+            replicationFactor = 0;
+          } else {
+            replicationFactor = coordinator.getReplicationFactorForSegment(segment.getId());
+          }
+          return new SegmentStatusInCluster(
+                   segment,
+                   isOvershadowed,
+                   replicationFactor
+               );
+        });
 
     final Function<SegmentStatusInCluster, Iterable<ResourceAction>> raGenerator = segment -> Collections
         .singletonList(AuthorizationUtils.DATASOURCE_READ_RA_GENERATOR.apply(segment.getDataSegment().getDataSource()));

sql/src/main/java/org/apache/druid/sql/calcite/schema/MetadataSegmentView.java

@@ -25,6 +25,8 @@
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.util.concurrent.Uninterruptibles;
 import com.google.inject.Inject;
+import org.apache.curator.shaded.com.google.common.cache.Cache;
+import org.apache.curator.shaded.com.google.common.cache.CacheBuilder;
 import org.apache.druid.client.BrokerSegmentWatcherConfig;
 import org.apache.druid.client.DataSegmentInterner;
 import org.apache.druid.client.JsonParserIterator;
@@ -40,6 +42,7 @@
 import org.apache.druid.metadata.SegmentsMetadataManager;
 import org.apache.druid.sql.calcite.planner.SegmentMetadataCacheConfig;
 import org.apache.druid.timeline.DataSegment;
+import org.apache.druid.timeline.SegmentId;
 import org.apache.druid.timeline.SegmentStatusInCluster;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
@@ -77,6 +80,7 @@ public class MetadataSegmentView
    */
   @MonotonicNonNull
   private volatile ImmutableSortedSet<SegmentStatusInCluster> publishedSegments = null;
+  private final Cache<SegmentId, Integer> segmentIdToReplicationFactor;
   private final ScheduledExecutorService scheduledExec;
   private final long pollPeriodInMS;
   private final LifecycleLock lifecycleLock = new LifecycleLock();
@@ -97,6 +101,9 @@ public MetadataSegmentView(
     this.isCacheEnabled = config.isMetadataSegmentCacheEnable();
     this.pollPeriodInMS = config.getMetadataSegmentPollPeriod();
     this.scheduledExec = Execs.scheduledSingleThreaded("MetadataSegmentView-Cache--%d");
+    this.segmentIdToReplicationFactor = CacheBuilder.newBuilder()
+                                                    .expireAfterWrite(3, TimeUnit.MINUTES)
+                                                    .build();
   }
 
   @LifecycleStart
@@ -143,10 +150,16 @@ private void poll()
     while (metadataSegments.hasNext()) {
       final SegmentStatusInCluster segment = metadataSegments.next();
       final DataSegment interned = DataSegmentInterner.intern(segment.getDataSegment());
+      Integer replicationFactor = segment.getReplicationFactor();
+      if (segment.getReplicationFactor() == null) {
+        replicationFactor = segmentIdToReplicationFactor.getIfPresent(segment.getDataSegment().getId());
+      } else {
+        segmentIdToReplicationFactor.put(segment.getDataSegment().getId(), segment.getReplicationFactor());
+      }
       final SegmentStatusInCluster segmentStatusInCluster = new SegmentStatusInCluster(
           interned,
           segment.isOvershadowed(),
-          segment.getReplicationFactor()
+          replicationFactor
       );
       builder.add(segmentStatusInCluster);
     }