---
id: index
title: "Data management"
sidebar_label: "Overview"
---

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Apache Druid stores data [partitioned by time chunk](../design/architecture.md#datasources-and-segments) in immutable
files called [segments](../design/segments.md). Data management operations involving replacing, or deleting,
these segments include:

- [Updates](update.md) to existing data.
- [Deletion](delete.md) of existing data.
- [Schema changes](schema-changes.md) for new and existing data.
- [Compaction](compaction.md) and [automatic compaction](automatic-compaction.md), which reindex existing data to
  optimize storage footprint and performance.