jon-wei commented on a change in pull request #7133: 6088 - Time Ordering On
Scans
URL: https://github.com/apache/incubator-druid/pull/7133#discussion_r263628213
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File path:
processing/src/main/java/org/apache/druid/query/scan/ScanQueryLimitRowIterator.java
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@@ -19,35 +19,59 @@
package org.apache.druid.query.scan;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Iterables;
+import org.apache.druid.java.util.common.UOE;
import org.apache.druid.java.util.common.guava.Sequence;
import org.apache.druid.java.util.common.guava.Yielder;
import org.apache.druid.java.util.common.guava.YieldingAccumulator;
import org.apache.druid.java.util.common.parsers.CloseableIterator;
+import org.apache.druid.query.Query;
import org.apache.druid.query.QueryPlus;
import org.apache.druid.query.QueryRunner;
import java.io.IOException;
+import java.util.ArrayList;
import java.util.List;
import java.util.Map;
+
+/**
+ * This iterator supports iteration through a Sequence returned by a
ScanResultValue QueryRunner. Its behaviour
+ * varies depending on whether the query is returning time-ordered values and
whether the CTX_KEY_OUTERMOST flag is
+ * set as false.
+ *
+ * Behaviours:
+ * 1) No time ordering: expects a Sequence of ScanResultValues which each
contain up to query.batchSize events.
+ * The iterator will be "done" when the limit of events is reached. The
final ScanResultValue might contain
+ * fewer than batchSize events so that the limit number of events is
returned.
+ * 2) Time Ordering, CTX_KEY_OUTERMOST==null or true: Same behaviour as no
time ordering
+ * 3) Time Ordering, CTX_KEY_OUTERMOST=false: The Sequence returned in this
case should contain ScanResultValues
+ * that contain only one event each. This iterator will perform batching
according to query.batchSize until
+ * the limit is reached.
+ */
public class ScanQueryLimitRowIterator implements
CloseableIterator<ScanResultValue>
{
+ private static final String TIME_ORDERING_SEGMENT_ID = "No segment ID
available when using time ordering";
Review comment:
hm, I would just make this an empty string to cut down on query result
sizes, I think it's enough to call out the behavior in the docs
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