akar-storage 0.1.17

Storage engine for the Akar embedded graph database
Documentation 
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//! Column statistics for cardinality estimation in the optimizer.

use std::collections::HashMap;

/// Statistics for a single column.
#[derive(Debug, Clone)]
pub struct ColumnStats {
    pub table_id: u64,
    pub column_id: u32,
    pub num_distinct_values: u64,
    pub num_null_values: u64,
    pub min_value: Option<Vec<u8>>,
    pub max_value: Option<Vec<u8>>,
}

/// Per-table statistics.
#[derive(Debug, Default)]
pub struct TableStats {
    pub num_rows: u64,
    pub columns: HashMap<u32, ColumnStats>,
}

/// Global statistics manager.
#[derive(Debug, Default)]
pub struct StatsStore {
    tables: HashMap<u64, TableStats>,
}

impl StatsStore {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn get_table_stats(&self, table_id: u64) -> Option<&TableStats> {
        self.tables.get(&table_id)
    }

    pub fn get_column_stats(&self, table_id: u64, column_id: u32) -> Option<&ColumnStats> {
        self.tables.get(&table_id).and_then(|t| t.columns.get(&column_id))
    }

    pub fn update_table_stats(&mut self, table_id: u64, stats: TableStats) {
        self.tables.insert(table_id, stats);
    }

    /// Get row count and estimated storage size for a table by ID.
    /// Returns (row_count: u64, storage_size_bytes: u64).
    pub fn table_stats_by_id(&self, table_id: u64) -> (u64, u64) {
        if let Some(stats) = self.tables.get(&table_id) {
            // Rough estimate: num_rows * 256 bytes per row average
            let estimated_size = stats.num_rows * 256;
            (stats.num_rows, estimated_size)
        } else {
            (0, 0)
        }
    }
}