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replication_strategy.go
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/
replication_strategy.go
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package ring
import (
"fmt"
)
// replicationStrategy decides, given the set of ingesters eligible for a key,
// which ingesters you will try and write to and how many failures you will
// tolerate.
// - Filters out dead ingesters so the one doesn't even try to write to them.
// - Checks there is enough ingesters for an operation to succeed.
// The ingesters argument may be overwritten.
func (r *Ring) replicationStrategy(ingesters []IngesterDesc, op Operation) ([]IngesterDesc, int, error) {
// We need a response from a quorum of ingesters, which is n/2 + 1. In the
// case of a node joining/leaving, the actual replica set might be bigger
// than the replication factor, so use the bigger or the two.
replicationFactor := r.cfg.ReplicationFactor
if len(ingesters) > replicationFactor {
replicationFactor = len(ingesters)
}
minSuccess := (replicationFactor / 2) + 1
maxFailure := replicationFactor - minSuccess
// Skip those that have not heartbeated in a while. NB these are still
// included in the calculation of minSuccess, so if too many failed ingesters
// will cause the whole write to fail.
for i := 0; i < len(ingesters); {
if r.IsHealthy(&ingesters[i], op) {
i++
} else {
ingesters = append(ingesters[:i], ingesters[i+1:]...)
maxFailure--
}
}
// This is just a shortcut - if there are not minSuccess available ingesters,
// after filtering out dead ones, don't even bother trying.
if maxFailure < 0 || len(ingesters) < minSuccess {
err := fmt.Errorf("at least %d live ingesters required, could only find %d",
minSuccess, len(ingesters))
return nil, 0, err
}
return ingesters, maxFailure, nil
}
// IsHealthy checks whether an ingester appears to be alive and heartbeating
func (r *Ring) IsHealthy(ingester *IngesterDesc, op Operation) bool {
return ingester.IsHealthy(op, r.cfg.HeartbeatTimeout)
}
// ReplicationFactor of the ring.
func (r *Ring) ReplicationFactor() int {
return r.cfg.ReplicationFactor
}
// IngesterCount is number of ingesters in the ring
func (r *Ring) IngesterCount() int {
r.mtx.Lock()
c := len(r.ringDesc.Ingesters)
r.mtx.Unlock()
return c
}