Update known issues

docs/multi-stage-query/known-issues.md

@@ -53,6 +53,9 @@ differs from SQL standard behavior, where columns are inserted based on position
 including the `createBitmapIndex` and `multiValueHandling` [dimension](../ingestion/ingestion-spec.md#dimension-objects)
 properties, and the `indexSpec` [`tuningConfig`](../ingestion/ingestion-spec.md#tuningconfig) property.
 
+- Queries using `EXTERN` to export data sometimes do not contain all the results. Certain rows maybe missing from the
+created files.
+
 ## `EXTERN` Function
 
 - The [schemaless dimensions](../ingestion/ingestion-spec.md#inclusions-and-exclusions)

docs/multi-stage-query/reference.md

@@ -336,7 +336,7 @@ The following table lists the context parameters for the MSQ task engine:
 | `faultTolerance` | SELECT, INSERT, REPLACE<br /><br /> Whether to turn on fault tolerance mode or not. Failed workers are retried based on [Limits](#limits). Cannot be used when `durableShuffleStorage` is explicitly set to false. | `false` |
 | `selectDestination` | SELECT<br /><br /> Controls where the final result of the select query is written. <br />Use `taskReport`(the default) to write select results to the task report. <b> This is not scalable since task reports size explodes for large results </b> <br/>Use `durableStorage` to write results to durable storage location. <b>For large results sets, its recommended to use `durableStorage` </b>. To configure durable storage see [`this`](#durable-storage) section. | `taskReport` |
 | `waitUntilSegmentsLoad` | INSERT, REPLACE<br /><br /> If set, the ingest query waits for the generated segment to be loaded before exiting, else the ingest query exits without waiting. The task and live reports contain the information about the status of loading segments if this flag is set. This will ensure that any future queries made after the ingestion exits will include results from the ingestion. The drawback is that the controller task will stall till the segments are loaded. | `false` |
-| `includeSegmentSource` | SELECT, INSERT, REPLACE<br /><br /> Controls the sources, which will be queried for results in addition to the segments present on deep storage. Can be `NONE` or `REALTIME`. If this value is `NONE`, only non-realtime (published and used) segments will be downloaded from deep storage. If this value is `REALTIME`, results will also be included from realtime tasks. | `NONE` |
+| `includeSegmentSource` | SELECT, INSERT, REPLACE<br /><br /> Controls the sources, which will be queried for results in addition to the segments present on deep storage. Can be `NONE` or `REALTIME`. If this value is `NONE`, only non-realtime (published and used) segments will be downloaded from deep storage. If this value is `REALTIME`, results will also be included from realtime tasks. `REALTIME` should not be used while writing data into the same datasource it is read from. This could potentially lead to incorrect data or missing results.| `NONE` |
 | `rowsPerPage` | SELECT<br /><br />The number of rows per page to target. The actual number of rows per page may be somewhat higher or lower than this number. In most cases, use the default.<br /> This property comes into effect only when `selectDestination` is set to `durableStorage` | 100000 |
 | `failOnEmptyInsert` | INSERT or REPLACE<br /><br /> When set to false (the default), an INSERT query generating no output rows will be no-op, and a REPLACE query generating no output rows will delete all data that matches the OVERWRITE clause. When set to true, an ingest query generating no output rows will throw an `InsertCannotBeEmpty` fault. | `false` |