datafusion_federation/
lib.rs

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mod optimizer;
mod plan_node;
pub mod schema_cast;
#[cfg(feature = "sql")]
pub mod sql;
mod table_provider;

use std::{
    fmt,
    hash::{Hash, Hasher},
    sync::Arc,
};

use datafusion::{
    execution::session_state::{SessionState, SessionStateBuilder},
    optimizer::{optimizer::Optimizer, OptimizerRule},
};

pub use optimizer::{get_table_source, FederationOptimizerRule};
pub use plan_node::{
    FederatedPlanNode, FederatedPlanner, FederatedQueryPlanner, FederationPlanner,
};
pub use table_provider::{FederatedTableProviderAdaptor, FederatedTableSource};

pub fn default_session_state() -> SessionState {
    let rules = default_optimizer_rules();
    SessionStateBuilder::new()
        .with_optimizer_rules(rules)
        .with_query_planner(Arc::new(FederatedQueryPlanner::new()))
        .with_default_features()
        .build()
}

pub fn default_optimizer_rules() -> Vec<Arc<dyn OptimizerRule + Send + Sync>> {
    // Get the default optimizer
    let df_default = Optimizer::new();
    let mut default_rules = df_default.rules;

    // Insert the FederationOptimizerRule after the ScalarSubqueryToJoin.
    // This ensures ScalarSubquery are replaced before we try to federate.
    let Some(pos) = default_rules
        .iter()
        .position(|x| x.name() == "scalar_subquery_to_join")
    else {
        panic!("Could not locate ScalarSubqueryToJoin");
    };

    // TODO: check if we should allow other optimizers to run before the federation rule.

    let federation_rule = Arc::new(FederationOptimizerRule::new());
    default_rules.insert(pos + 1, federation_rule);

    default_rules
}

pub type FederationProviderRef = Arc<dyn FederationProvider>;
pub trait FederationProvider: Send + Sync {
    // Returns the name of the provider, used for comparison.
    fn name(&self) -> &str;

    // Returns the compute context in which this federation provider
    // will execute a query. For example: database instance & catalog.
    fn compute_context(&self) -> Option<String>;

    // Returns an optimizer that can cut out part of the plan
    // to federate it.
    fn optimizer(&self) -> Option<Arc<Optimizer>>;
}

impl fmt::Display for dyn FederationProvider {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{} {:?}", self.name(), self.compute_context())
    }
}

impl PartialEq<dyn FederationProvider> for dyn FederationProvider {
    /// Comparing name, args and return_type
    fn eq(&self, other: &dyn FederationProvider) -> bool {
        self.name() == other.name() && self.compute_context() == other.compute_context()
    }
}

impl Hash for dyn FederationProvider {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.name().hash(state);
        self.compute_context().hash(state);
    }
}

impl Eq for dyn FederationProvider {}