Function scan_shared_segment

nodedb/src/engine/timeseries/columnar_bridge.rs:164–197

Scan a shared-format segment for timeseries data with time-range filtering. Uses block-level predicate pushdown: blocks whose timestamp range doesn't overlap `[start_ms, end_ms]` are skipped entirely (not decompressed). `ts_col_idx` is the timestamp column index (typically 0). `val_col_idx` is the value column index to read.

(
    segment_data: &[u8],
    ts_col_idx: usize,
    val_col_idx: usize,
    start_ms: i64,
    end_ms: i64,
)

/// `ts_col_idx` is the timestamp column index (typically 0).
/// `val_col_idx` is the value column index to read.
pub fn scan_shared_segment(
    segment_data: &[u8],
    ts_col_idx: usize,
    val_col_idx: usize,
    start_ms: i64,
    end_ms: i64,
) -> Result<TsScanResult, nodedb_columnar::ColumnarError> {
    let reader = SegmentReader::open(segment_data)?;

    // Build predicates for block-level time-range skip.
    // Timestamp blocks with max < start or min > end can be skipped.
    // Use the lossless i64 constructors so that timestamps outside ±2^53
    // (which don't round-trip through f64 exactly) are compared correctly
    // against the exact min_i64/max_i64 fields written by BlockStats::integer().
    let predicates = vec![
        ScanPredicate::gte_i64(ts_col_idx, start_ms),
        ScanPredicate::lte_i64(ts_col_idx, end_ms),
    ];

    // Read timestamp column with predicate pushdown.
    let ts_decoded = reader.read_column_filtered(ts_col_idx, &predicates)?;
    let (timestamps, ts_valid) = decoded_to_i64(ts_decoded);

    // Read value column with same predicate pushdown (ensures row alignment).
    let val_decoded = reader.read_column_filtered(val_col_idx, &predicates)?;
    let (values, val_valid) = decoded_to_f64(val_decoded);

    Ok(TsScanResult {
        timestamps,
        values,
        ts_valid,
        val_valid,
    })
}

/// Scan a shared-format segment, returning only rows within a time range.
///