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Improve comments for Layer trait.

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This commit is contained in:
anastasia
2021-09-02 15:24:22 +03:00
parent cee366ac17
commit 66174c0342
2 changed files with 18 additions and 5 deletions
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7
pageserver/src/layered_repository/layer_map.rs
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@@ -271,15 +271,16 @@ impl LayerMap {
/// Is there a newer image layer for given segment?
///
/// This is used for garbage collection, to determine if an old layer can
/// be deleted. We ignore in-memory layers because they are not durable
/// on disk, and delta layers because they depend on an older layer.
/// be deleted.
pub fn newer_image_layer_exists(&self, seg: SegmentTag, lsn: Lsn) -> bool {
if let Some(segentry) = self.segs.get(&seg) {
// We only check on-disk layers, because
// in-memory layers are not durable
for (newer_lsn, layer) in segentry
.historic
.range((Included(lsn), Included(Lsn(u64::MAX))))
{
// Ignore delta layers.
// Ignore layers that depend on an older layer.
if layer.is_incremental() {
continue;
}

16
pageserver/src/layered_repository/storage_layer.rs
View File

@@ -105,12 +105,24 @@ pub enum PageReconstructResult {
/// in-memory and on-disk layers.
///
pub trait Layer: Send + Sync {
// These functions identify the relish segment and the LSN range
// that this Layer holds.
/// Identify the timeline this relish belongs to
fn get_timeline_id(&self) -> ZTimelineId;
/// Identify the relish segment
fn get_seg_tag(&self) -> SegmentTag;
/// Inclusive start bound of the LSN range that this layer hold
fn get_start_lsn(&self) -> Lsn;
/// 'end_lsn' meaning depends on the layer kind:
/// - in-memory layer is either unbounded (end_lsn = MAX_LSN) or dropped (end_lsn = drop_lsn)
/// - image layer represents snapshot at one LSN, so end_lsn = lsn
/// - delta layer has end_lsn
///
/// TODO Is end_lsn always exclusive for all layer kinds?
fn get_end_lsn(&self) -> Lsn;
/// Is the segment represented by this layer dropped by PostgreSQL?
fn is_dropped(&self) -> bool;
/// Filename used to store this layer on disk. (Even in-memory layers