add apache license

docs/data-management/compaction.md

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   ~ specific language governing permissions and limitations
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 Query performance in Apache Druid depends on optimally sized segments. Compaction is one strategy you can use to optimize segment size for your Druid database. Compaction tasks read an existing set of segments for a given time interval and combine the data into a new "compacted" set of segments. In some cases the compacted segments are larger, but there are fewer of them. In other cases the compacted segments may be smaller. Compaction tends to increase performance because optimized segments require less per-segment processing and less memory overhead for ingestion and for querying paths.
 
 ## Compaction guidelines

docs/data-management/manual-compaction.md

@@ -3,6 +3,25 @@ id: manual-compaction
 title: "Manual compaction"
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 In Apache Druid, compaction is a special type of ingestion task that reads data from a Druid datasource and writes it back into the same datasource. A common use case for this is to [optimally size segments](../operations/segment-optimization.md) after ingestion to improve query performance.
 
 You can perform manual compaction where you submit a one-time compaction task for a specific interval. Generally, you don't need to do this if you use [automatic compaction](./automatic-compaction.md), which is recommended for most workloads.