TrueCloudLab/frostfs-sdk-go
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netmap: sort buckets by HRW value

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If weights for some buckets are equal, result depends on the
initial positions of buckets in slice. Thus we sort buckets by value
using hash of the first node as a have for the whole bucket.
This is ok, because buckets are already sorted by HRW.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>
This commit is contained in:
Evgenii Stratonikov 2021-12-24 14:31:34 +03:00 • committed by Alex Vanin
parent f7582399ed
commit 3edaf9ecb6
3 changed files with 192 additions and 2 deletions
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7
netmap/selector.go
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@ -58,8 +58,11 @@ func (c *Context) getSelection(p *PlacementPolicy, s *Selector) ([]Nodes, error)
return nil, fmt.Errorf("%w: '%s'", ErrNotEnoughNodes, s.Name())
}
// We need deterministic output in case there is no pivot.
// If pivot is set, buckets are sorted by HRW.
// However, because initial order influences HRW order for buckets with equal weights,
// we also need to have deterministic input to HRW sorting routine.
if len(c.pivot) == 0 {
// Deterministic order in case of zero seed.
if s.Attribute() == "" {
sort.Slice(buckets, func(i, j int) bool {
return buckets[i].nodes[0].ID < buckets[j].nodes[0].ID
@ -98,7 +101,7 @@ func (c *Context) getSelection(p *PlacementPolicy, s *Selector) ([]Nodes, error)
weights[i] = GetBucketWeight(nodes[i], c.aggregator(), c.weightFunc)
}
hrw.SortSliceByWeightIndex(nodes, weights, c.pivotHash)
hrw.SortSliceByWeightValue(nodes, weights, c.pivotHash)
}
if s.Attribute() == "" {