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Slight change and add comment to layout assignation algo
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1 changed files with 33 additions and 37 deletions
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@ -175,47 +175,32 @@ impl ClusterLayout {
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// Get old partition assignation
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let old_partitions = self.parse_assignation_data();
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// Create new partition assignation starting from old one
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let mut partitions = old_partitions.clone();
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// Cleanup steps in new partition assignation:
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let min_keep_nodes_per_part = (self.replication_factor + 1) / 2;
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for part in partitions.iter_mut() {
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// - remove from assignation nodes that don't have a role in the layout anymore
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part.nodes
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.retain(|(_, info)| info.map(|x| x.capacity.is_some()).unwrap_or(false));
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// - remove from assignation some nodes that are in the same datacenter
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// if we can, so that the later steps can ensure datacenter variety
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// as much as possible (but still under the constraint that each partition
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// should not move from at least a certain number of nodes that is
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// min_keep_nodes_per_part)
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'rmloop: while part.nodes.len() > min_keep_nodes_per_part {
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let mut zns_c = HashMap::<&str, usize>::new();
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for (_id, info) in part.nodes.iter() {
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*zns_c.entry(info.unwrap().zone.as_str()).or_insert(0) += 1;
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}
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for i in 0..part.nodes.len() {
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if zns_c[part.nodes[i].1.unwrap().zone.as_str()] > 1 {
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part.nodes.remove(i);
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continue 'rmloop;
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// Start new partition assignation with nodes from old assignation where it is relevant
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let mut partitions = old_partitions
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.iter()
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.map(|old_part| {
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let mut new_part = PartitionAss::new();
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for node in old_part.nodes.iter() {
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if let Some(role) = node.1 {
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if role.capacity.is_some() {
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new_part.add(None, n_zones, node.0, role);
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}
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}
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}
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new_part
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})
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.collect::<Vec<_>>();
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break;
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}
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}
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// When nodes are removed, or when bootstraping an assignation from
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// scratch for a new cluster, the old partitions will have holes (or be empty).
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// Here we add more nodes to make a complete (sub-optimal) assignation,
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// In various cases, not enough nodes will have been added for all partitions
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// in the step above (e.g. due to node removals, or new zones being added).
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// Here we add more nodes to make a complete (but sub-optimal) assignation,
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// using an initial partition assignation that is calculated using the multi-dc maglev trick
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match self.initial_partition_assignation() {
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Some(initial_partitions) => {
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for (part, ipart) in partitions.iter_mut().zip(initial_partitions.iter()) {
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for (id, info) in ipart.nodes.iter() {
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if part.nodes.len() < self.replication_factor {
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part.add(part.nodes.len() + 1, n_zones, id, info.unwrap());
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part.add(None, n_zones, id, info.unwrap());
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}
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}
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assert!(part.nodes.len() == self.replication_factor);
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@ -287,7 +272,7 @@ impl ClusterLayout {
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let mut newpart = part.clone();
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newpart.nodes.remove(irm);
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if !newpart.add(newpart.nodes.len() + 1, n_zones, idadd, infoadd) {
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if !newpart.add(None, n_zones, idadd, infoadd) {
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continue;
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}
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assert!(newpart.nodes.len() == self.replication_factor);
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@ -422,7 +407,7 @@ impl ClusterLayout {
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continue;
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}
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for (pos2, &qv) in q.iter().enumerate().skip(*pos) {
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if partitions[qv].add(rep + 1, n_zones, node_id, node_info) {
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if partitions[qv].add(Some(rep + 1), n_zones, node_id, node_info) {
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remaining -= 1;
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*pos = pos2 + 1;
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break;
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@ -579,15 +564,26 @@ impl<'a> PartitionAss<'a> {
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}
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}
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// add is a key function in creating a PartitionAss, i.e. the list of nodes
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// to which a partition is assigned. It tries to add a certain node id to the
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// assignation, but checks that doing so is compatible with the NECESSARY
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// condition that the partition assignation must be dispersed over different
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// zones (datacenters) if enough zones exist. This is why it takes a n_zones
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// parameter, which is the total number of zones that have existing nodes:
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// if nodes in the assignation already cover all n_zones zones, then any node
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// that is not yet in the assignation can be added. Otherwise, only nodes
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// that are in a new zone can be added.
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fn add(
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&mut self,
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target_len: usize,
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target_len: Option<usize>,
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n_zones: usize,
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node: &'a Uuid,
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role: &'a NodeRole,
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) -> bool {
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if self.nodes.len() != target_len - 1 {
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return false;
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if let Some(tl) = target_len {
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if self.nodes.len() != tl - 1 {
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return false;
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}
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}
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let p_zns = self
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