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pageserver: clean up GcCutoffs names (#8379)

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- `horizon` is a confusing term, it's not at all obvious that this means
space-based retention limit, rather than the total GC history limit.
Rename to `GcCutoffs::space`.
- `pitr` is less confusing, but still an unecessary level of indirection
from what we really mean: a time-based condition. The fact that we use
that that time-history for Point In Time Recovery doesn't mean we have
to refer to time as "pitr" everywhere. Rename to `GcCutoffs::time`.
This commit is contained in:
John Spray
2024-07-16 14:54:54 +01:00
committed by GitHub
parent d2ee760eb2
commit a40b402957
4 changed files with 75 additions and 98 deletions
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14
pageserver/src/tenant.rs
View File

@@ -2912,7 +2912,7 @@ impl Tenant {
if let Some(ancestor_id) = timeline.get_ancestor_timeline_id() {
if let Some(ancestor_gc_cutoffs) = gc_cutoffs.get(&ancestor_id) {
target.within_ancestor_pitr =
timeline.get_ancestor_lsn() >= ancestor_gc_cutoffs.pitr;
timeline.get_ancestor_lsn() >= ancestor_gc_cutoffs.time;
}
}
@@ -2928,7 +2928,7 @@ impl Tenant {
timeline.metrics.pitr_history_size.set(
timeline
.get_last_record_lsn()
.checked_sub(target.cutoffs.pitr)
.checked_sub(target.cutoffs.time)
.unwrap_or(Lsn(0))
.0,
);
@@ -4262,7 +4262,7 @@ mod tests {
.source()
.unwrap()
.to_string()
.contains("is earlier than latest GC horizon"));
.contains("is earlier than latest GC cutoff"));
}
}
@@ -6718,8 +6718,8 @@ mod tests {
{
// Update GC info
let mut guard = tline.gc_info.write().unwrap();
guard.cutoffs.pitr = Lsn(0x30);
guard.cutoffs.horizon = Lsn(0x30);
guard.cutoffs.time = Lsn(0x30);
guard.cutoffs.space = Lsn(0x30);
}
let expected_result = [
@@ -7109,8 +7109,8 @@ mod tests {
*guard = GcInfo {
retain_lsns: vec![],
cutoffs: GcCutoffs {
pitr: Lsn(0x30),
horizon: Lsn(0x30),
time: Lsn(0x30),
space: Lsn(0x30),
},
leases: Default::default(),
within_ancestor_pitr: false,

61
pageserver/src/tenant/size.rs
View File

@@ -135,11 +135,9 @@ pub struct TimelineInputs {
ancestor_lsn: Lsn,
last_record: Lsn,
latest_gc_cutoff: Lsn,
horizon_cutoff: Lsn,
pitr_cutoff: Lsn,
/// Cutoff point based on GC settings
next_gc_cutoff: Lsn,
next_pitr_cutoff: Lsn,
/// Cutoff point calculated from the user-supplied 'max_retention_period'
retention_param_cutoff: Option<Lsn>,
@@ -150,7 +148,7 @@ pub struct TimelineInputs {
/// Gathers the inputs for the tenant sizing model.
///
/// Tenant size does not consider the latest state, but only the state until next_gc_cutoff, which
/// Tenant size does not consider the latest state, but only the state until next_pitr_cutoff, which
/// is updated on-demand, during the start of this calculation and separate from the
/// [`TimelineInputs::latest_gc_cutoff`].
///
@@ -158,11 +156,8 @@ pub struct TimelineInputs {
///
/// ```text
/// 0-----|---------|----|------------| · · · · · |·> lsn
/// initdb_lsn branchpoints* next_gc_cutoff latest
/// initdb_lsn branchpoints* next_pitr_cutoff latest
/// ```
///
/// Until gc_horizon_cutoff > `Timeline::last_record_lsn` for any of the tenant's timelines, the
/// tenant size will be zero.
pub(super) async fn gather_inputs(
tenant: &Tenant,
limit: &Arc<Semaphore>,
@@ -172,7 +167,7 @@ pub(super) async fn gather_inputs(
cancel: &CancellationToken,
ctx: &RequestContext,
) -> Result<ModelInputs, CalculateSyntheticSizeError> {
// refresh is needed to update gc related pitr_cutoff and horizon_cutoff
// refresh is needed to update [`timeline::GcCutoffs`]
tenant.refresh_gc_info(cancel, ctx).await?;
// Collect information about all the timelines
@@ -236,20 +231,18 @@ pub(super) async fn gather_inputs(
// we don't consider the `Timeline::disk_consistent_lsn` at all, because we are not
// actually removing files.
//
// We only consider [`GcInfo::pitr_cutoff`], and not [`GcInfo::horizon_cutoff`], because from
// We only consider [`timeline::GcCutoffs::time`], and not [`timeline::GcCutoffs::space`], because from
// a user's perspective they have only requested retention up to the time bound (pitr_cutoff), rather
// than a space bound (horizon cutoff). This means that if someone drops a database and waits for their
// than our internal space cutoff. This means that if someone drops a database and waits for their
// PITR interval, they will see synthetic size decrease, even if we are still storing data inside
// horizon_cutoff.
let pitr_cutoff = gc_info.cutoffs.pitr;
let horizon_cutoff = gc_info.cutoffs.horizon;
let mut next_gc_cutoff = pitr_cutoff;
// the space cutoff.
let mut next_pitr_cutoff = gc_info.cutoffs.time;
// If the caller provided a shorter retention period, use that instead of the GC cutoff.
let retention_param_cutoff = if let Some(max_retention_period) = max_retention_period {
let param_cutoff = Lsn(last_record_lsn.0.saturating_sub(max_retention_period));
if next_gc_cutoff < param_cutoff {
next_gc_cutoff = param_cutoff;
if next_pitr_cutoff < param_cutoff {
next_pitr_cutoff = param_cutoff;
}
Some(param_cutoff)
} else {
@@ -263,7 +256,7 @@ pub(super) async fn gather_inputs(
.copied()
.collect::<Vec<_>>();
// next_gc_cutoff in parent branch are not of interest (right now at least), nor do we
// next_pitr_cutoff in parent branch are not of interest (right now at least), nor do we
// want to query any logical size before initdb_lsn.
let branch_start_lsn = cmp::max(ancestor_lsn, timeline.initdb_lsn);
@@ -291,10 +284,10 @@ pub(super) async fn gather_inputs(
)
}
// Add a point for the GC cutoff
let branch_start_needed = next_gc_cutoff <= branch_start_lsn;
// Add a point for the PITR cutoff
let branch_start_needed = next_pitr_cutoff <= branch_start_lsn;
if !branch_start_needed {
lsns.push((next_gc_cutoff, LsnKind::GcCutOff));
lsns.push((next_pitr_cutoff, LsnKind::GcCutOff));
}
lsns.sort_unstable();
@@ -333,7 +326,7 @@ pub(super) async fn gather_inputs(
parent: Some(parent),
lsn: lsn.0,
size: None,
needed: lsn > next_gc_cutoff,
needed: lsn > next_pitr_cutoff,
},
timeline_id: timeline.timeline_id,
kind,
@@ -357,8 +350,8 @@ pub(super) async fn gather_inputs(
segment: Segment {
parent: Some(lease_parent),
lsn: lsn.0,
size: None, // Filled in later, if necessary
needed: lsn > next_gc_cutoff, // only needed if the point is within rentention.
size: None, // Filled in later, if necessary
needed: lsn > next_pitr_cutoff, // only needed if the point is within rentention.
},
timeline_id: timeline.timeline_id,
kind: LsnKind::LeaseStart,
@@ -398,9 +391,7 @@ pub(super) async fn gather_inputs(
last_record: last_record_lsn,
// this is not used above, because it might not have updated recently enough
latest_gc_cutoff: *timeline.get_latest_gc_cutoff_lsn(),
horizon_cutoff,
pitr_cutoff,
next_gc_cutoff,
next_pitr_cutoff,
retention_param_cutoff,
lease_points,
});
@@ -742,9 +733,7 @@ fn verify_size_for_multiple_branches() {
"ancestor_lsn": "0/18D3D98",
"last_record": "0/2230CD0",
"latest_gc_cutoff": "0/1698C48",
"horizon_cutoff": "0/2210CD0",
"pitr_cutoff": "0/2210CD0",
"next_gc_cutoff": "0/2210CD0",
"next_pitr_cutoff": "0/2210CD0",
"retention_param_cutoff": null,
"lease_points": []
},
@@ -753,9 +742,7 @@ fn verify_size_for_multiple_branches() {
"ancestor_lsn": "0/176D998",
"last_record": "0/1837770",
"latest_gc_cutoff": "0/1698C48",
"horizon_cutoff": "0/1817770",
"pitr_cutoff": "0/1817770",
"next_gc_cutoff": "0/1817770",
"next_pitr_cutoff": "0/1817770",
"retention_param_cutoff": null,
"lease_points": []
},
@@ -764,9 +751,7 @@ fn verify_size_for_multiple_branches() {
"ancestor_lsn": "0/0",
"last_record": "0/18D3D98",
"latest_gc_cutoff": "0/1698C48",
"horizon_cutoff": "0/18B3D98",
"pitr_cutoff": "0/18B3D98",
"next_gc_cutoff": "0/18B3D98",
"next_pitr_cutoff": "0/18B3D98",
"retention_param_cutoff": null,
"lease_points": []
}
@@ -820,9 +805,7 @@ fn verify_size_for_one_branch() {
"ancestor_lsn": "0/0",
"last_record": "47/280A5860",
"latest_gc_cutoff": "47/240A5860",
"horizon_cutoff": "47/240A5860",
"pitr_cutoff": "47/240A5860",
"next_gc_cutoff": "47/240A5860",
"next_pitr_cutoff": "47/240A5860",
"retention_param_cutoff": "0/0",
"lease_points": []
}

94
pageserver/src/tenant/timeline.rs
View File

@@ -478,37 +478,32 @@ impl GcInfo {
}
}
/// The `GcInfo` component describing which Lsns need to be retained.
/// The `GcInfo` component describing which Lsns need to be retained. Functionally, this
/// is a single number (the oldest LSN which we must retain), but it internally distinguishes
/// between time-based and space-based retention for observability and consumption metrics purposes.
#[derive(Debug)]
pub(crate) struct GcCutoffs {
/// Keep everything newer than this point.
///
/// This is calculated by subtracting 'gc_horizon' setting from
/// last-record LSN
///
/// FIXME: is this inclusive or exclusive?
pub(crate) horizon: Lsn,
/// Calculated from the [`TenantConf::gc_horizon`], this LSN indicates how much
/// history we must keep to retain a specified number of bytes of WAL.
pub(crate) space: Lsn,
/// In addition to 'retain_lsns' and 'horizon_cutoff', keep everything newer than this
/// point.
///
/// This is calculated by finding a number such that a record is needed for PITR
/// if only if its LSN is larger than 'pitr_cutoff'.
pub(crate) pitr: Lsn,
/// Calculated from [`TenantConf::pitr_interval`], this LSN indicates how much
/// history we must keep to enable reading back at least the PITR interval duration.
pub(crate) time: Lsn,
}
impl Default for GcCutoffs {
fn default() -> Self {
Self {
horizon: Lsn::INVALID,
pitr: Lsn::INVALID,
space: Lsn::INVALID,
time: Lsn::INVALID,
}
}
}
impl GcCutoffs {
fn select_min(&self) -> Lsn {
std::cmp::min(self.horizon, self.pitr)
std::cmp::min(self.space, self.time)
}
}
@@ -867,7 +862,7 @@ impl Timeline {
let gc_info = self.gc_info.read().unwrap();
let history = self
.get_last_record_lsn()
.checked_sub(gc_info.cutoffs.pitr)
.checked_sub(gc_info.cutoffs.time)
.unwrap_or(Lsn(0))
.0;
(history, gc_info.within_ancestor_pitr)
@@ -1566,7 +1561,7 @@ impl Timeline {
) -> anyhow::Result<()> {
ensure!(
lsn >= **latest_gc_cutoff_lsn,
"LSN {} is earlier than latest GC horizon {} (we might've already garbage collected needed data)",
"LSN {} is earlier than latest GC cutoff {} (we might've already garbage collected needed data)",
lsn,
**latest_gc_cutoff_lsn,
);
@@ -4944,18 +4939,18 @@ impl Timeline {
/// garbage collection.
///
/// We calculate two cutoffs, one based on time and one based on WAL size. `pitr`
/// controls the time cutoff (or ZERO to disable time-based retention), and `cutoff_horizon` controls
/// controls the time cutoff (or ZERO to disable time-based retention), and `space_cutoff` controls
/// the space-based retention.
///
/// This function doesn't simply to calculate time & space based retention: it treats time-based
/// retention as authoritative if enabled, and falls back to space-based retention if calculating
/// the LSN for a time point isn't possible. Therefore the GcCutoffs::horizon in the response might
/// be different to the `cutoff_horizon` input. Callers should treat the min() of the two cutoffs
/// be different to the `space_cutoff` input. Callers should treat the min() of the two cutoffs
/// in the response as the GC cutoff point for the timeline.
#[instrument(skip_all, fields(timeline_id=%self.timeline_id))]
pub(super) async fn find_gc_cutoffs(
&self,
cutoff_horizon: Lsn,
space_cutoff: Lsn,
pitr: Duration,
cancel: &CancellationToken,
ctx: &RequestContext,
@@ -4972,8 +4967,8 @@ impl Timeline {
// Unit tests which specify zero PITR interval expect to avoid doing any I/O for timestamp lookup
if pitr == Duration::ZERO {
return Ok(GcCutoffs {
pitr: self.get_last_record_lsn(),
horizon: cutoff_horizon,
time: self.get_last_record_lsn(),
space: space_cutoff,
});
}
}
@@ -4981,8 +4976,7 @@ impl Timeline {
// Calculate a time-based limit on how much to retain:
// - if PITR interval is set, then this is our cutoff.
// - if PITR interval is not set, then we do a lookup
// based on DEFAULT_PITR_INTERVAL, so that size-based retention (horizon)
// does not result in keeping history around permanently on idle databases.
// based on DEFAULT_PITR_INTERVAL, so that size-based retention does not result in keeping history around permanently on idle databases.
let time_cutoff = {
let now = SystemTime::now();
let time_range = if pitr == Duration::ZERO {
@@ -5023,31 +5017,31 @@ impl Timeline {
// PITR is not set. Retain the size-based limit, or the default time retention,
// whichever requires less data.
GcCutoffs {
pitr: std::cmp::max(time_cutoff, cutoff_horizon),
horizon: std::cmp::max(time_cutoff, cutoff_horizon),
time: self.get_last_record_lsn(),
space: std::cmp::max(time_cutoff, space_cutoff),
}
}
(Duration::ZERO, None) => {
// PITR is not set, and time lookup failed
GcCutoffs {
pitr: self.get_last_record_lsn(),
horizon: cutoff_horizon,
time: self.get_last_record_lsn(),
space: space_cutoff,
}
}
(_, None) => {
// PITR interval is set & we didn't look up a timestamp successfully. Conservatively assume PITR
// cannot advance beyond what was already GC'd, and respect space-based retention
GcCutoffs {
pitr: *self.get_latest_gc_cutoff_lsn(),
horizon: cutoff_horizon,
time: *self.get_latest_gc_cutoff_lsn(),
space: space_cutoff,
}
}
(_, Some(time_cutoff)) => {
// PITR interval is set and we looked up timestamp successfully. Ignore
// size based retention and make time cutoff authoritative
GcCutoffs {
pitr: time_cutoff,
horizon: time_cutoff,
time: time_cutoff,
space: time_cutoff,
}
}
})
@@ -5074,11 +5068,11 @@ impl Timeline {
return Err(GcError::TimelineCancelled);
}
let (horizon_cutoff, pitr_cutoff, retain_lsns, max_lsn_with_valid_lease) = {
let (space_cutoff, time_cutoff, retain_lsns, max_lsn_with_valid_lease) = {
let gc_info = self.gc_info.read().unwrap();
let horizon_cutoff = min(gc_info.cutoffs.horizon, self.get_disk_consistent_lsn());
let pitr_cutoff = gc_info.cutoffs.pitr;
let space_cutoff = min(gc_info.cutoffs.space, self.get_disk_consistent_lsn());
let time_cutoff = gc_info.cutoffs.time;
let retain_lsns = gc_info.retain_lsns.clone();
// Gets the maximum LSN that holds the valid lease.
@@ -5088,14 +5082,14 @@ impl Timeline {
let max_lsn_with_valid_lease = gc_info.leases.last_key_value().map(|(lsn, _)| *lsn);
(
horizon_cutoff,
pitr_cutoff,
space_cutoff,
time_cutoff,
retain_lsns,
max_lsn_with_valid_lease,
)
};
let mut new_gc_cutoff = Lsn::min(horizon_cutoff, pitr_cutoff);
let mut new_gc_cutoff = Lsn::min(space_cutoff, time_cutoff);
let standby_horizon = self.standby_horizon.load();
// Hold GC for the standby, but as a safety guard do it only within some
// reasonable lag.
@@ -5124,8 +5118,8 @@ impl Timeline {
let res = self
.gc_timeline(
horizon_cutoff,
pitr_cutoff,
space_cutoff,
time_cutoff,
retain_lsns,
max_lsn_with_valid_lease,
new_gc_cutoff,
@@ -5143,8 +5137,8 @@ impl Timeline {
async fn gc_timeline(
&self,
horizon_cutoff: Lsn,
pitr_cutoff: Lsn,
space_cutoff: Lsn,
time_cutoff: Lsn,
retain_lsns: Vec<Lsn>,
max_lsn_with_valid_lease: Option<Lsn>,
new_gc_cutoff: Lsn,
@@ -5205,22 +5199,22 @@ impl Timeline {
result.layers_total += 1;
// 1. Is it newer than GC horizon cutoff point?
if l.get_lsn_range().end > horizon_cutoff {
if l.get_lsn_range().end > space_cutoff {
debug!(
"keeping {} because it's newer than horizon_cutoff {}",
"keeping {} because it's newer than space_cutoff {}",
l.layer_name(),
horizon_cutoff,
space_cutoff,
);
result.layers_needed_by_cutoff += 1;
continue 'outer;
}
// 2. It is newer than PiTR cutoff point?
if l.get_lsn_range().end > pitr_cutoff {
if l.get_lsn_range().end > time_cutoff {
debug!(
"keeping {} because it's newer than pitr_cutoff {}",
"keeping {} because it's newer than time_cutoff {}",
l.layer_name(),
pitr_cutoff,
time_cutoff,
);
result.layers_needed_by_pitr += 1;
continue 'outer;

4
pageserver/src/tenant/timeline/compaction.rs
View File

@@ -195,7 +195,7 @@ impl Timeline {
tracing::info!(
"latest_gc_cutoff: {}, pitr cutoff {}",
*latest_gc_cutoff,
self.gc_info.read().unwrap().cutoffs.pitr
self.gc_info.read().unwrap().cutoffs.time
);
let layers = self.layers.read().await;
@@ -990,7 +990,7 @@ impl Timeline {
"enhanced legacy compaction currently does not support retain_lsns (branches)"
)));
}
let gc_cutoff = Lsn::min(gc_info.cutoffs.horizon, gc_info.cutoffs.pitr);
let gc_cutoff = gc_info.cutoffs.select_min();
let mut selected_layers = Vec::new();
// TODO: consider retain_lsns
drop(gc_info);