Struct RowHeader 

#[repr(C, align(8))]
pub struct RowHeader {
    pub xmin: u64,
    pub xmax: u64,
    pub flags: u8,
}

Per-row MVCC visibility header.

24 bytes after alignment (8 + 8 + 1 + 7 padding). The padding is intentional: a power-of-two stride keeps array indexing cheap and matches the cache-line layout PG uses for HeapTupleHeaderData.

Fields

xmin: u64

Version that wrote this row (= TxId of the inserting tx at commit time). Compared against the reader’s snapshot version to decide visibility.

Default XMIN_FROZEN = 1 on rows loaded from a pre- v7.37.15 envelope.

xmax: u64

Version that deleted / updated this row, or XMAX_ALIVE = 0 when still alive. UPDATE writes xmax on the old row + xmin on the new one inside the same transaction.

flags: u8

Bit-packed flags. See module-level constants. The most common state (xmin frozen, xmax alive) sets only HEAP_XMIN_FROZEN so visibility checks can short-circuit on the flags & HEAP_XMIN_FROZEN == HEAP_XMIN_FROZEN && xmax == 0 fast path.

Implementations

impl RowHeader

pub const fn frozen() -> RowHeader

The canonical “frozen, alive” header. Use on rows loaded from a pre-v7.37.15 envelope and on rows inserted before the writer transaction is assigned a TxId.

pub const fn alive(xmin: u64) -> RowHeader

A header for a row inserted by transaction xmin, still alive. Default for fresh INSERTs.

pub const fn is_all_visible_fast(&self) -> bool

True iff this header is the all-visible fast path (frozen + alive). The visibility-map bit is true exactly when EVERY header in a segment satisfies this — letting scans skip the per-row check entirely for cold segments.

pub const fn is_deleted(&self) -> bool

Was this row deleted? false when xmax == XMAX_ALIVE.

Trait Implementations

impl Clone for RowHeader

fn clone(&self) -> RowHeader

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for RowHeader

impl Debug for RowHeader

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for RowHeader

fn default() -> RowHeader

Returns the “default value” for a type.

impl Eq for RowHeader

impl PartialEq for RowHeader

fn eq(&self, other: &RowHeader) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for RowHeader