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mk3 optimization

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This commit is contained in:
John Spray
2024-12-05 09:28:35 +00:00
parent 5bb7472eab
commit e3b8a3ee57
1 changed files with 164 additions and 79 deletions
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243
storage_controller/src/tenant_shard.rs
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@@ -727,6 +727,59 @@ impl TenantShard {
Ok(())
}
/// Returns None if the current location's score is unavailable, i.e. cannot draw a conclusion
fn is_better_location(
&self,
scheduler: &mut Scheduler,
schedule_context: &ScheduleContext,
current: NodeId,
candidate: NodeId,
) -> Option<bool> {
let Some(candidate_score) = scheduler.compute_node_score::<NodeAttachmentSchedulingScore>(
candidate,
&self.preferred_az_id,
schedule_context,
) else {
// The candidate node is unavailable for scheduling or otherwise couldn't get a score
return None;
};
match scheduler.compute_node_score::<NodeAttachmentSchedulingScore>(
current,
&self.preferred_az_id,
schedule_context,
) {
Some(current_score) => {
// Ignore utilization components when comparing scores: we don't want to migrate
// because of transient load variations, it risks making the system thrash, and
// migrating for utilization requires a separate high level view of the system to
// e.g. prioritize moving larger or smaller tenants, rather than arbitrarily
// moving things around in the order that we hit this function.
let candidate_score = candidate_score.for_optimization();
let current_score = current_score.for_optimization();
if candidate_score < current_score {
tracing::info!("Found a lower scoring location! {candidate} is better than {current} ({candidate_score:?} is better than {current_score:?})");
Some(true)
} else {
// The candidate node is no better than our current location, so don't migrate
tracing::debug!(
"Candidate node {candidate} is no better than our current location {current} (candidate {candidate_score:?} vs current {current_score:?})",
);
Some(false)
}
}
None => {
// The current node is unavailable for scheduling, so we can't make any sensible
// decisions about optimisation. This should be a transient state -- if the node
// is offline then it will get evacuated, if is blocked by a scheduling mode
// then we will respect that mode by doing nothing.
tracing::debug!("Current node {current} is unavailable for scheduling");
None
}
}
}
fn find_better_location(
&self,
scheduler: &mut Scheduler,
@@ -744,13 +797,13 @@ impl TenantShard {
// Construct a schedule context that excludes locations belonging to
// this shard: this simulates removing and re-scheduling the shard
let schedule_context = schedule_context.project_detach(self);
// let schedule_context = schedule_context.project_detach(self);
// Look for a lower-scoring location to attach to
let Ok(candidate_node) = scheduler.schedule_shard::<AttachedShardTag>(
&[], // Don't hard-exclude anything: we want to consider the possibility of migrating to somewhere we already have a secondary
&self.preferred_az_id,
&schedule_context,
schedule_context,
) else {
// A scheduling error means we have no possible candidate replacements
tracing::debug!("No candidate node found");
@@ -775,54 +828,8 @@ impl TenantShard {
return None;
}
// Consider whether the candidate is any better than our current location once the
// context is updated to reflect the migration.
let Some(candidate_score) = scheduler.compute_node_score::<NodeAttachmentSchedulingScore>(
candidate_node,
&self.preferred_az_id,
&schedule_context,
) else {
// The candidate node is unavailable for scheduling or otherwise couldn't get a score
// This is unexpected, because schedule() yielded this node
debug_assert!(false);
return None;
};
match scheduler.compute_node_score::<NodeAttachmentSchedulingScore>(
attached,
&self.preferred_az_id,
&schedule_context,
) {
Some(current_score) => {
// Ignore utilization components when comparing scores: we don't want to migrate
// because of transient load variations, it risks making the system thrash, and
// migrating for utilization requires a separate high level view of the system to
// e.g. prioritize moving larger or smaller tenants, rather than arbitrarily
// moving things around in the order that we hit this function.
let candidate_score = candidate_score.for_optimization();
let current_score = current_score.for_optimization();
if candidate_score < current_score {
tracing::info!("Found a lower scoring location! {candidate_score:?} is better than {current_score:?}");
} else {
// The candidate node is no better than our current location, so don't migrate
tracing::debug!(
"Candidate node {candidate_node} is no better than our current location {attached} (candidate {candidate_score:?} vs attached {current_score:?})",
);
return None;
}
}
None => {
// The current node is unavailable for scheduling, so we can't make any sensible
// decisions about optimisation. This should be a transient state -- if the node
// is offline then it will get evacuated, if is blocked by a scheduling mode
// then we will respect that mode by doing nothing.
tracing::debug!("Current node {attached} is unavailable for scheduling");
return None;
}
}
Some(candidate_node)
self.is_better_location(scheduler, schedule_context, attached, candidate_node)
.and_then(|better| if better { Some(candidate_node) } else { None })
}
/// Optimize attachments: if a shard has a secondary location that is preferable to
@@ -836,7 +843,75 @@ impl TenantShard {
) -> Option<ScheduleOptimization> {
let attached = (*self.intent.get_attached())?;
let replacement = self.find_better_location(scheduler, schedule_context);
let schedule_context = schedule_context.project_detach(self);
// If we already have a secondary that is higher-scoring than out current location,
// then simply migrate to it.
for secondary in self.intent.get_secondary() {
if let Some(true) =
self.is_better_location(scheduler, &schedule_context, attached, *secondary)
{
return Some(ScheduleOptimization {
sequence: self.sequence,
action: ScheduleOptimizationAction::MigrateAttachment(MigrateAttachment {
old_attached_node_id: attached,
new_attached_node_id: *secondary,
}),
});
}
}
// Given that none of our current secondaries is a better location than our current
// attached location (checked above), we may trim any secondaries that are not needed
// for the placement policy.
if self.intent.get_secondary().len() > self.policy.want_secondaries() {
// This code path cleans up extra secondaries after migrating, and/or
// trims extra secondaries after a PlacementPolicy::Attached(N) was
// modified to decrease N.
let mut secondary_scores = self
.intent
.get_secondary()
.iter()
.map(|node_id| {
(
*node_id,
scheduler.compute_node_score::<NodeSecondarySchedulingScore>(
*node_id,
&self.preferred_az_id,
&schedule_context,
),
)
})
.collect::<Vec<_>>();
if secondary_scores.iter().any(|score| score.1.is_none()) {
// Don't have full list of scores, so can't make a good decision about which to drop unless
// there is an obvious one in the wrong AZ
for secondary in self.intent.get_secondary() {
if scheduler.get_node_az(secondary) == self.preferred_az_id {
return Some(ScheduleOptimization {
sequence: self.sequence,
action: ScheduleOptimizationAction::RemoveSecondary(*secondary),
});
}
}
// Fall through: we didn't identify one to remove. This ought to be rare.
tracing::warn!("Keeping extra secondaries: can't determine which of {:?} to remove (some nodes offline?)",
self.intent.get_secondary()
);
} else {
secondary_scores.sort_by_key(|score| score.1.unwrap());
let victim = secondary_scores.last().unwrap().0;
return Some(ScheduleOptimization {
sequence: self.sequence,
action: ScheduleOptimizationAction::RemoveSecondary(victim),
});
}
}
let replacement = self.find_better_location(scheduler, &schedule_context);
// We have found a candidate and confirmed that its score is preferable
// to our current location. See if we have a secondary location in the preferred location already: if not,
@@ -866,34 +941,34 @@ impl TenantShard {
}),
})
}
} else if self.intent.get_secondary().len() > self.policy.want_secondaries() {
// We aren't in the process of migrating anywhere, and we're attached in our preferred AZ. If there are
// any other secondary locations in our preferred AZ, we presume they were created to facilitate a migration
// of the attached location, and remove them.
for secondary in self.intent.get_secondary() {
if scheduler.get_node_az(secondary) == self.preferred_az_id {
tracing::info!(
"Identified optimization({}): remove secondary {secondary}",
self.tenant_shard_id
);
return Some(ScheduleOptimization {
sequence: self.sequence,
action: ScheduleOptimizationAction::RemoveSecondary(*secondary),
});
}
}
// } else if self.intent.get_secondary().len() > self.policy.want_secondaries() {
// // We aren't in the process of migrating anywhere, and we're attached in our preferred AZ. If there are
// // any other secondary locations in our preferred AZ, we presume they were created to facilitate a migration
// // of the attached location, and remove them.
// for secondary in self.intent.get_secondary() {
// if scheduler.get_node_az(secondary) == self.preferred_az_id {
// tracing::info!(
// "Identified optimization({}): remove secondary {secondary}",
// self.tenant_shard_id
// );
// return Some(ScheduleOptimization {
// sequence: self.sequence,
// action: ScheduleOptimizationAction::RemoveSecondary(*secondary),
// });
// }
// }
// Fall through: maybe we had excess secondaries in other AZs? Trim them in an arbitrary order
// (lowest Node ID first).
let mut secondary_node_ids = self.intent.get_secondary().clone();
secondary_node_ids.sort();
let victim = secondary_node_ids
.first()
.expect("Within block for > check on secondary count");
Some(ScheduleOptimization {
sequence: self.sequence,
action: ScheduleOptimizationAction::RemoveSecondary(*victim),
})
// // Fall through: maybe we had excess secondaries in other AZs? Trim them in an arbitrary order
// // (lowest Node ID first).
// let mut secondary_node_ids = self.intent.get_secondary().clone();
// secondary_node_ids.sort();
// let victim = secondary_node_ids
// .first()
// .expect("Within block for > check on secondary count");
// Some(ScheduleOptimization {
// sequence: self.sequence,
// action: ScheduleOptimizationAction::RemoveSecondary(*victim),
// })
} else {
// We didn't find somewhere we'd rather be, and we don't have any excess secondaries
// to clean up: no action required.
@@ -2026,7 +2101,7 @@ pub(crate) mod tests {
optimization_a_cleanup,
Some(ScheduleOptimization {
sequence: shard_a.sequence,
action: ScheduleOptimizationAction::RemoveSecondary(NodeId(2))
action: ScheduleOptimizationAction::RemoveSecondary(NodeId(3))
})
);
shard_a.apply_optimization(&mut scheduler, optimization_a_cleanup.unwrap());
@@ -2190,6 +2265,11 @@ pub(crate) mod tests {
for shard in shards.iter_mut() {
let optimization = shard.optimize_attachment(scheduler, &schedule_context);
tracing::info!(
"optimize_attachment({})={:?}",
shard.tenant_shard_id,
optimization
);
if let Some(optimization) = optimization {
optimizations.push(optimization.clone());
shard.apply_optimization(scheduler, optimization);
@@ -2198,6 +2278,11 @@ pub(crate) mod tests {
}
let optimization = shard.optimize_secondary(scheduler, &schedule_context);
tracing::info!(
"optimize_secondary({})={:?}",
shard.tenant_shard_id,
optimization
);
if let Some(optimization) = optimization {
optimizations.push(optimization.clone());
shard.apply_optimization(scheduler, optimization);