[GitHub] [druid] vtlim commented on a change in pull request #11550: SQL: Add is_active to sys.segments, update examples and docs.

[GitBox <gi...@apache.org>]

vtlim commented on a change in pull request #11550:
URL: https://github.com/apache/druid/pull/11550#discussion_r774106454



##########
File path: docs/querying/sql.md
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@@ -1193,20 +1193,23 @@ Segments table provides details on all Druid segments, whether they are publishe
 |version|STRING|Version string (generally an ISO8601 timestamp corresponding to when the segment set was first started). Higher version means the more recently created segment. Version comparing is based on string comparison.|
 |partition_num|LONG|Partition number (an integer, unique within a datasource+interval+version; may not necessarily be contiguous)|
 |num_replicas|LONG|Number of replicas of this segment currently being served|
-|num_rows|LONG|Number of rows in current segment, this value could be null if unknown to Broker at query time|
-|is_published|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 represents this segment has been published to the metadata store with `used=1`. See the [Architecture page](../design/architecture.md#segment-lifecycle) for more details.|
-|is_available|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 if this segment is currently being served by any process(Historical or realtime). See the [Architecture page](../design/architecture.md#segment-lifecycle) for more details.|
-|is_realtime|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 if this segment is _only_ served by realtime tasks, and 0 if any historical process is serving this segment.|
-|is_overshadowed|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 if this segment is published and is _fully_ overshadowed by some other published segments. Currently, is_overshadowed is always false for unpublished segments, although this may change in the future. You can filter for segments that "should be published" by filtering for `is_published = 1 AND is_overshadowed = 0`. Segments can briefly be both published and overshadowed if they were recently replaced, but have not been unpublished yet. See the [Architecture page](../design/architecture.md#segment-lifecycle) for more details.|
+|num_rows|LONG|Number of rows in this segment, or zero if the number of rows is not known.<br /><br />This row count is gathered by the Broker in the background. It will be zero if the Broker has not gathered a row count for this segment yet. For segments ingested from streams, the reported row count may lag behind the result of a `count(*)` query because the cached `num_rows` on the Broker may be out of date. This will settle shortly after new rows stop being written to that particular segment.|
+|is_active|LONG|True for segments that represent the latest state of a datasource.<br /><br />Equivalent to `(is_published = 1 AND is_overshadowed = 0) OR is_realtime = 1`. In steady state, when no ingestion or data management operations are happening, `is_active` will be equivalent to `is_available`. However, they may differ from each other when ingestion or data management operations have executed recently. In these cases, Druid will load and unload segments appropriately to bring actual availability in line with the expected state given by `is_active`.|
+|is_published|LONG|Boolean represented as long type where 1 = true, 0 = false. 1 if this segment has been published to the metadata store and is marked as used. See the [segment lifecycle documentation](../design/architecture.md#segment-lifecycle) for more details.|
+|is_available|LONG|Boolean represented as long type where 1 = true, 0 = false. 1 if this segment is currently being served by any data serving process, like a Historical or a realtime ingestion task. See the [segment lifecycle documentation](../design/architecture.md#segment-lifecycle) for more details.|
+|is_realtime|LONG|Boolean represented as long type where 1 = true, 0 = false. 1 if this segment is _only_ served by realtime tasks, and 0 if any Historical process is serving this segment.|
+|is_overshadowed|LONG|Boolean represented as long type where 1 = true, 0 = false. 1 if this segment is published and is _fully_ overshadowed by some other published segments. Currently, `is_overshadowed` is always 0 for unpublished segments, although this may change in the future. You can filter for segments that "should be published" by filtering for `is_published = 1 AND is_overshadowed = 0`. Segments can briefly be both published and overshadowed if they were recently replaced, but have not been unpublished yet. See the [segment lifecycle documentation](../design/architecture.md#segment-lifecycle) for more details.|
 |shard_spec|STRING|JSON-serialized form of the segment `ShardSpec`|
 |dimensions|STRING|JSON-serialized form of the segment dimensions|
 |metrics|STRING|JSON-serialized form of the segment metrics|
 |last_compaction_state|STRING|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.|
 
-For example to retrieve all segments for datasource "wikipedia", use the query:
+For example to retrieve all currently-active segments for datasource "wikipedia", use the query:

Review comment:
       ```suggestion
   For example to retrieve all currently active segments for datasource "wikipedia", use the query:
   ```




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