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| id: sql-overview |
| title: Pulsar SQL Overview |
| sidebar_label: "Overview" |
| original_id: sql-overview |
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| Apache Pulsar is used to store streams of event data, and the event data is structured with predefined fields. With the implementation of the [Schema Registry](schema-get-started.md), you can store structured data in Pulsar and query the data by using [Presto](https://prestosql.io/). |
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| As the core of Pulsar SQL, Presto Pulsar connector enables Presto workers within a Presto cluster to query data from Pulsar. |
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| The query performance is efficient and highly scalable, because Pulsar adopts [two level segment based architecture](concepts-architecture-overview.md#apache-bookkeeper). |
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| Topics in Pulsar are stored as segments in [Apache BookKeeper](https://bookkeeper.apache.org/). Each topic segment is replicated to some BookKeeper nodes, which enables concurrent reads and high read throughput. You can configure the number of BookKeeper nodes, and the default number is `3`. In Presto Pulsar connector, data is read directly from BookKeeper, so Presto workers can read concurrently from horizontally scalable number BookKeeper nodes. |
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