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54 lines
1.8 KiB
Markdown
54 lines
1.8 KiB
Markdown
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# Tuning Salsa
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## LRU Cache
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You can specify an LRU cache size for any non-input query:
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```rs
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let lru_capacity: usize = 128;
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base_db::ParseQuery.in_db_mut(self).set_lru_capacity(lru_capacity);
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```
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The default is `0`, which disables LRU-caching entirely.
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See [The LRU RFC for more details](./rfcs/RFC0004-LRU.md).
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Note that there is no garbage collection for keys and
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results of old queries, so LRU caches are currently the
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only knob available for avoiding unbounded memory usage
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for long-running apps built on Salsa.
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## Intern Queries
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Intern queries can make key lookup cheaper, save memory, and
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avoid the need for [`Arc`](https://doc.rust-lang.org/std/sync/struct.Arc.html).
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Interning is especially useful for queries that involve nested,
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tree-like data structures.
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See:
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- The [Intern Queries RFC](./rfcs/RFC0002-Intern-Queries.md)
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- The [`compiler` example](https://github.com/salsa-rs/salsa/blob/master/examples/compiler/main.rs),
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which uses interning.
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## Granularity of Incrementality
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See:
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- [common patterns: selection](./common_patterns/selection.md) and
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- The [`selection` example](https://github.com/salsa-rs/salsa/blob/master/examples/selection/main.rs)
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## Cancellation
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Queries that are no longer needed due to concurrent writes or changes in dependencies are cancelled
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by Salsa. Each accesss of an intermediate query is a potential cancellation point. cancellation is
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implemented via panicking, and Salsa internals are intended to be panic-safe.
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If you have a query that contains a long loop which does not execute any intermediate queries,
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salsa won't be able to cancel it automatically. You may wish to check for cancellation yourself
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by invoking `db.unwind_if_cancelled()`.
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For more details on cancellation, see:
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- [the Opinionated cancellation RFC](./rfcs/RFC0007-Opinionated-Cancelation.md).
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- The tests for cancellation behavior in the Salsa repo.
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