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Brendan Clement
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The existing docs have 254 findings from our shared Vale rules. Contributors would otherwise inherit these when editing the same lines. Clean up the prose across 80 pages: correct product names and a repeated word, simplify a few phrases, and replace dashes with punctuation that fits each sentence. The pinned Vale scan now reports zero findings, with no suppressions.
54 lines
2.1 KiB
Plaintext
54 lines
2.1 KiB
Plaintext
---
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title: "Explain"
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sidebarTitle: "Explain"
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description: "EXPLAIN, EXPLAIN ANALYZE and EXPLAIN VERBOSE: reading and measuring a plan from SQL."
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icon: map
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keywords: ["explain", "explain analyze", "explain verbose", "query plan"]
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---
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<Badge color="red">Enterprise</Badge> [SQL runs in LanceDB Enterprise.](/sql)
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```sql
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EXPLAIN SELECT * FROM documents WHERE identifier < 1000
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EXPLAIN ANALYZE SELECT * FROM documents WHERE identifier < 1000
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```
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| Statement | What it returns |
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| --- | --- |
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| `EXPLAIN <query>` | Logical and physical plan, without executing the query. |
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| `EXPLAIN ANALYZE <query>` | Executes the query and annotates each operator with runtime metrics (rows, timing). |
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| `EXPLAIN VERBOSE <query>` | Adds intermediate optimizer plans on top of `EXPLAIN`. |
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The result is a small relation with `plan_type` and `plan` columns, read
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through the same client you use for regular queries. See
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[Connecting](/sql#connecting).
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SQL plans and the SDK's
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[`explain_plan` and `analyze_plan`](/search/explain) output share scan and index
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operators. Use the same approach to inspect index coverage and filter pushdown;
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SQL can also add joins, aggregates and other operators:
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<CardGroup cols={2}>
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<Card title="What it shows" icon="map" href="/search/explain#inspect-a-query-plan">
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Reading a plan: operators, pushdown, index usage.
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</Card>
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<Card title="What it measures" icon="gauge" href="/search/explain#analyze-a-query-plan">
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Reading the metrics, and a worked before/after.
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</Card>
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</CardGroup>
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## What to look for {#what-to-look-for}
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| Sign | Means |
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| --- | --- |
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| `ScalarIndexQuery` | the predicate used a scalar index |
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| `LanceScan` with high `bytes_read` | inspect the selected columns, filter pushdown and index use |
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| `FilterExec` above a search | the filter ran after search rather than pushing into it |
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| `ANNSubIndex` / `ANNIvfPartition` | the vector index was used |
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A `LanceScan` feeding a join is the common one worth acting on. See
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[Joins](/sql/dql/join#performance).
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For a table's columns and types without a plan, see
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[`DESCRIBE`](/sql/ddl/table#describe).
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