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StatsProvider

reddb::storage::query::planner

Trait StatsProvider 

Source 
pub trait StatsProvider: Send + Sync {
    // Required methods
    fn table_stats(&self, table: &str) -> Option<TableStats>;
    fn index_stats(&self, table: &str, column: &str) -> Option<IndexStats>;

    // Provided methods
    fn column_stats(&self, table: &str, column: &str) -> Option<ColumnStats> { ... }
    fn has_index(&self, table: &str, column: &str) -> bool { ... }
    fn distinct_values(&self, table: &str, column: &str) -> Option<u64> { ... }
    fn column_histogram(&self, _table: &str, _column: &str) -> Option<Histogram> { ... }
    fn column_mcv(
        &self,
        _table: &str,
        _column: &str,
    ) -> Option<MostCommonValues> { ... }
}
Expand description

Read-only interface the planner uses to look up storage statistics.

Implementations must be cheap (O(1) or O(log n)) — the planner calls these during plan construction and must not block on I/O. Pre-aggregate expensive data into memory before exposing a provider.

Required Methods§

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fn table_stats(&self, table: &str) -> Option<TableStats>

Return row-count / page-count / column metadata for table, or None when stats are not available.

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fn index_stats(&self, table: &str, column: &str) -> Option<IndexStats>

Return the IndexStats backing a secondary index on (table, column), if one exists. The planner uses IndexStats::point_selectivity to derive equality selectivity instead of the 0.01 constant.

Provided Methods§

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fn column_stats(&self, table: &str, column: &str) -> Option<ColumnStats>

Return per-column statistics (distinct count, null count, min/max) when available. Default implementation derives from StatsProvider::table_stats when present.

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fn has_index(&self, table: &str, column: &str) -> bool

Convenience: does a usable index exist on (table, column)?

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fn distinct_values(&self, table: &str, column: &str) -> Option<u64>

Convenience: distinct-value count for a column, via column stats or an index on that column, whichever is available.

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fn column_histogram(&self, _table: &str, _column: &str) -> Option<Histogram>

Optional equi-depth histogram for the column. Defaults to None, in which case the planner falls back to its uniform 0.3 range heuristic.

Implementations should sample once and cache — this is called during plan construction and must not block on I/O.

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fn column_mcv(&self, _table: &str, _column: &str) -> Option<MostCommonValues>

Optional most-common-values list for the column. Defaults to None, in which case the planner falls back to its uniform 0.01 equality heuristic. Use for skewed columns where one or two values dominate the table.

Implementors§