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> **Documentation Index:** Fetch the complete configuration index at https://ydb.tech/docs/en/llms.txt

# YDB Concepts

This documentation section covers the fundamental concepts and architectural principles behind YDB. This information will help you better understand what's going on when you follow more practical content that can be found in [other sections tailored for specific roles](#see-also).

The following topics provide comprehensive coverage of YDB's core functionality, from high-level architecture and data models to advanced features like transactions, indexing, and federated queries.

- [Glossary](https://ydb.tech/docs/en/concepts/glossary.md?version=v25.4)
- [Architecture](https://ydb.tech/docs/en/concepts/architecture.md?version=v25.4)
- [Connecting to a database](https://ydb.tech/docs/en/concepts/connect.md?version=v25.4)
- [Schema objects](https://ydb.tech/docs/en/concepts/datamodel/index.md?version=v25.4)
- [Cluster topology](https://ydb.tech/docs/en/concepts/topology.md?version=v25.4)
- [Transactions](https://ydb.tech/docs/en/concepts/transactions.md?version=v25.4)
- [Secondary indexes](https://ydb.tech/docs/en/concepts/query_execution/secondary_indexes.md?version=v25.4)
- [Vector search](https://ydb.tech/docs/en/concepts/query_execution/vector_search.md?version=v25.4)
- [Change Data Capture (CDC)](https://ydb.tech/docs/en/concepts/cdc.md?version=v25.4)
- [Time to live and eviction](https://ydb.tech/docs/en/concepts/ttl.md?version=v25.4)
- [Database limits](https://ydb.tech/docs/en/concepts/limits-ydb.md?version=v25.4)
- [Multi-Version Concurrency Control (MVCC)](https://ydb.tech/docs/en/concepts/query_execution/mvcc.md?version=v25.4)
- [Asynchronous replication](https://ydb.tech/docs/en/concepts/async-replication.md?version=v25.4)
- [Query optimizer](https://ydb.tech/docs/en/concepts/query_execution/optimizer.md?version=v25.4)
- [Federated queries](https://ydb.tech/docs/en/concepts/query_execution/federated_query/index.md?version=v25.4)
- [Streaming queries](https://ydb.tech/docs/en/concepts/streaming-query.md?version=v25.4)

## See Also {#see-also}

- [YDB for DevOps Engineers](https://ydb.tech/docs/en/devops/index.md?version=v25.4)
- [YDB for Application Developers / Software Engineers](https://ydb.tech/docs/en/dev/index.md?version=v25.4)
- [YDB for Security Engineers](https://ydb.tech/docs/en/security/index.md?version=v25.4)