docs: Add upgrade notes for Druid 29.0.0 (#16022)

docs/release-info/upgrade-notes.md

@@ -26,6 +26,69 @@ The upgrade notes assume that you are upgrading from the Druid version that imme
 
 For the full release notes for a specific version, see the [releases page](https://github.com/apache/druid/releases).
 
+## 29.0.0
+
+### Upgrade notes
+
+#### Changed `equals` filter for native queries
+
+The [equality filter](https://druid.apache.org/docs/latest/querying/filters#equality-filter) on mixed type `auto` columns that contain arrays must now be filtered as their presenting type. This means that if any rows are arrays (for example, the segment metadata and `information_schema` reports the type as some array type), then the native queries must also filter as if they are some array type.
+ 
+This change impacts mixed type `auto` columns that contain both scalars and arrays. It doesn't impact SQL, which already has this limitation due to how the type presents itself.
+
+[#15503](https://github.com/apache/druid/pull/15503)
+
+#### Console automatically sets `arrayIngestMode` for MSQ queries
+
+Druid console now configures the `arrayIngestMode` parameter in the data loading flow, and its value can persist across the SQL tab unless manually updated. When loading multi-value dimensions or arrays in the Druid console, note the value of the `arrayIngestMode` parameter to prevent mixing multi-value dimensions and arrays in the same column of a data source.
+
+[#15588](https://github.com/apache/druid/pull/15588)
+
+#### Improved concurrent append and replace (experimental)
+
+You no longer have to manually determine the task lock type for concurrent append and replace (experimental) with the `taskLockType` task context. Instead, Druid can now determine it automatically for you. You can use the context parameter `"useConcurrentLocks": true` for individual tasks and datasources or enable concurrent append and replace at a cluster level using `druid.indexer.task.default.context`.
+
+[#15684](https://github.com/apache/druid/pull/15684)
+
+#### Enabled empty ingest queries
+
+The MSQ task engine now allows empty ingest queries by default. For queries that don't generate any output rows, the MSQ task engine reports zero values for `numTotalRows` and `totalSizeInBytes` instead of null. Previously, ingest queries that produced no data would fail with the `InsertCannotBeEmpty` MSQ fault.
+
+To revert to the original behavior, set the MSQ query parameter `failOnEmptyInsert` to `true`.
+
+[#15495](https://github.com/apache/druid/pull/15495) [#15674](https://github.com/apache/druid/pull/15674)
+
+#### Enabled query request queuing by default when total laning is turned on
+
+When query scheduler threads are less than server HTTP threads, total laning turns on.
+This reserves some HTTP threads for non-query requests such as health checks.
+The total laning previously would reject any query request that exceeds the lane capacity.
+Now, excess requests will instead be queued with a timeout equal to `MIN(Integer.MAX_VALUE, druid.server.http.maxQueryTimeout)`.
+
+[#15440](https://github.com/apache/druid/pull/15440)
+
+#### Changed how empty or null array columns are stored
+
+Columns ingested with the auto column indexer that contain only empty or null arrays are now stored as `ARRAY<LONG\>` instead of `COMPLEX<json\>`.
+
+[#15505](https://github.com/apache/druid/pull/15505)
+
+#### Changed how Druid allocates weekly segments
+
+When the requested granularity is a month or larger but a segment can't be allocated, Druid resorts to day partitioning.
+Unless explicitly specified, Druid skips week-granularity segments for data partitioning because these segments don't align with the end of the month or more coarse-grained intervals.
+
+Previously, if Druid couldn't allocate segments by month, it tried allocating them by week next.
+In the new behavior, Druid skips partitioning by week and goes directly to day. Week segments can only be allocated if the chosen partitioning in the append task is WEEK.
+
+[#15589](https://github.com/apache/druid/pull/15589)
+
+#### Removed the `auto` search strategy
+
+Removed the `auto` search strategy from the native search query. Setting `searchStrategy` to `auto` is now equivalent to `useIndexes`.
+
+[#15550](https://github.com/apache/druid/pull/15550)
+
 ## 28.0.0
 
 ### Upgrade notes