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Small change to partition assignation algorithm

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This change helps ensure that nodes for each partition are spread
over all datacenters, a property that wasn't ensured previously
when going from a 2 DC deployment to a 3 DC deployment
This commit is contained in:
Alex Auvolat 2022-02-10 16:10:21 +01:00
parent 43945234ae
commit 413ab0eaed
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GPG key ID: 0E496D15096376BE
2 changed files with 37 additions and 9 deletions
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18
src/garage/cli/layout.rs
View file

@ -196,6 +196,15 @@ pub async fn cmd_apply_layout(
) -> Result<(), Error> {
let mut layout = fetch_layout(rpc_cli, rpc_host).await?;
layout.roles.merge(&layout.staging);
if !layout.calculate_partition_assignation() {
return Err(Error::Message("Could not calculate new assignation of partitions to nodes. This can happen if there are less nodes than the desired number of copies of your data (see the replication_mode configuration parameter).".into()));
}
layout.staging.clear();
layout.staging_hash = blake2sum(&rmp_to_vec_all_named(&layout.staging).unwrap()[..]);
match apply_opt.version {
None => {
println!("Please pass the --version flag to ensure that you are writing the correct version of the cluster layout.");
@ -209,15 +218,6 @@ pub async fn cmd_apply_layout(
}
}
layout.roles.merge(&layout.staging);
if !layout.calculate_partition_assignation() {
return Err(Error::Message("Could not calculate new assignation of partitions to nodes. This can happen if there are less nodes than the desired number of copies of your data (see the replication_mode configuration parameter).".into()));
}
layout.staging.clear();
layout.staging_hash = blake2sum(&rmp_to_vec_all_named(&layout.staging).unwrap()[..]);
layout.version += 1;
send_layout(rpc_cli, rpc_host, layout).await?;

28
src/rpc/layout.rs
View file

@ -172,12 +172,38 @@ impl ClusterLayout {
println!("Calculating updated partition assignation, this may take some time...");
println!();
// 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();
// 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
@ -196,6 +222,8 @@ impl ClusterLayout {
}
}
None => {
// Not enough nodes in cluster to build a correct assignation.
// Signal it by returning an error.
return false;
}
}