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Slight change and add comment to layout assignation algo

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This commit is contained in:
Alex Auvolat 2022-03-16 14:42:42 +01:00
parent 413ab0eaed
commit 7e0e2ffda2
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GPG Key ID: 0E496D15096376BE
1 changed files with 33 additions and 37 deletions
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72
src/rpc/layout.rs
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@ -175,47 +175,32 @@ impl ClusterLayout {
// Get old partition assignation
let old_partitions = self.parse_assignation_data();
// Create new partition assignation starting from old one
let mut partitions = old_partitions.clone();
// Start new partition assignation with nodes from old assignation where it is relevant
let mut partitions = old_partitions
.iter()
.map(|old_part| {
let mut new_part = PartitionAss::new();
for node in old_part.nodes.iter() {
if let Some(role) = node.1 {
if role.capacity.is_some() {
new_part.add(None, n_zones, node.0, role);
}
}
}
new_part
})
.collect::<Vec<_>>();
// Cleanup steps in new partition assignation:
let min_keep_nodes_per_part = (self.replication_factor + 1) / 2;
for part in partitions.iter_mut() {
// - remove from assignation nodes that don't have a role in the layout anymore
part.nodes
.retain(|(_, info)| info.map(|x| x.capacity.is_some()).unwrap_or(false));
// - remove from assignation some nodes that are in the same datacenter
// if we can, so that the later steps can ensure datacenter variety
// as much as possible (but still under the constraint that each partition
// should not move from at least a certain number of nodes that is
// min_keep_nodes_per_part)
'rmloop: while part.nodes.len() > min_keep_nodes_per_part {
let mut zns_c = HashMap::<&str, usize>::new();
for (_id, info) in part.nodes.iter() {
*zns_c.entry(info.unwrap().zone.as_str()).or_insert(0) += 1;
}
for i in 0..part.nodes.len() {
if zns_c[part.nodes[i].1.unwrap().zone.as_str()] > 1 {
part.nodes.remove(i);
continue 'rmloop;
}
}
break;
}
}
// When nodes are removed, or when bootstraping an assignation from
// scratch for a new cluster, the old partitions will have holes (or be empty).
// Here we add more nodes to make a complete (sub-optimal) assignation,
// In various cases, not enough nodes will have been added for all partitions
// in the step above (e.g. due to node removals, or new zones being added).
// Here we add more nodes to make a complete (but sub-optimal) assignation,
// using an initial partition assignation that is calculated using the multi-dc maglev trick
match self.initial_partition_assignation() {
Some(initial_partitions) => {
for (part, ipart) in partitions.iter_mut().zip(initial_partitions.iter()) {
for (id, info) in ipart.nodes.iter() {
if part.nodes.len() < self.replication_factor {
part.add(part.nodes.len() + 1, n_zones, id, info.unwrap());
part.add(None, n_zones, id, info.unwrap());
}
}
assert!(part.nodes.len() == self.replication_factor);
@ -287,7 +272,7 @@ impl ClusterLayout {
let mut newpart = part.clone();
newpart.nodes.remove(irm);
if !newpart.add(newpart.nodes.len() + 1, n_zones, idadd, infoadd) {
if !newpart.add(None, n_zones, idadd, infoadd) {
continue;
}
assert!(newpart.nodes.len() == self.replication_factor);
@ -422,7 +407,7 @@ impl ClusterLayout {
continue;
}
for (pos2, &qv) in q.iter().enumerate().skip(*pos) {
if partitions[qv].add(rep + 1, n_zones, node_id, node_info) {
if partitions[qv].add(Some(rep + 1), n_zones, node_id, node_info) {
remaining -= 1;
*pos = pos2 + 1;
break;
@ -579,16 +564,27 @@ impl<'a> PartitionAss<'a> {
}
}
// add is a key function in creating a PartitionAss, i.e. the list of nodes
// to which a partition is assigned. It tries to add a certain node id to the
// assignation, but checks that doing so is compatible with the NECESSARY
// condition that the partition assignation must be dispersed over different
// zones (datacenters) if enough zones exist. This is why it takes a n_zones
// parameter, which is the total number of zones that have existing nodes:
// if nodes in the assignation already cover all n_zones zones, then any node
// that is not yet in the assignation can be added. Otherwise, only nodes
// that are in a new zone can be added.
fn add(
&mut self,
target_len: usize,
target_len: Option<usize>,
n_zones: usize,
node: &'a Uuid,
role: &'a NodeRole,
) -> bool {
if self.nodes.len() != target_len - 1 {
if let Some(tl) = target_len {
if self.nodes.len() != tl - 1 {
return false;
}
}
let p_zns = self
.nodes