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Add note about guardrails on WHERE … IN … #1899

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Add note about guardrails on WHERE … IN … #1899

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9 changes: 9 additions & 0 deletions manual/core/statements/simple/README.md
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Expand Up @@ -144,6 +144,15 @@ session.execute(
// Invalid amount of bind variables
```

> **NOTE:**
> Guardrails ensure consistent behavior by limiting the number of partition keys selected by an `IN` restriction and the cartesian product of multiple `IN` restrictions.
>
> **Example 1:** Providing a `WHERE` clause with a high number of elements in the `IN` clause (not part of the same partitions) causes the coordinator receiving the request to trigger other internal requests to cope, making
> one node unnecessarily busy. Instead, distribute a simple request with `WHERE` and a single value.
>
> **Example 2:** Using more than 25 values in the `IN` clause is an invalid pattern because the load is transferred from the client to the coordinator. Use parallel queries and reduce on the client side for faster speed and
> to distribute the load on the nodes.

### Type inference

Another consequence of not parsing query strings is that the driver has to guess how to serialize
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