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dnsdist: do not iterate over hash map for chashed based query distribution #6939

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merged 1 commit into from Sep 25, 2018
Merged

dnsdist: do not iterate over hash map for chashed based query distribution #6939

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25 changes: 12 additions & 13 deletions pdns/dnsdist.cc
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Expand Up @@ -775,10 +775,10 @@ shared_ptr<DownstreamState> whashed(const NumberedServerVector& servers, const D

shared_ptr<DownstreamState> chashed(const NumberedServerVector& servers, const DNSQuestion* dq)
{
std::map<unsigned int, shared_ptr<DownstreamState>> circle = {};
unsigned int qhash = dq->qname->hash(g_hashperturb);
unsigned int sel = 0, max = 0;
shared_ptr<DownstreamState> ret = nullptr, last = nullptr;
unsigned int sel = std::numeric_limits<unsigned int>::max();
unsigned int min = std::numeric_limits<unsigned int>::max();
shared_ptr<DownstreamState> ret = nullptr, first = nullptr;

for (const auto& d: servers) {
if (d.second->isUp()) {
Expand All @@ -790,27 +790,26 @@ shared_ptr<DownstreamState> chashed(const NumberedServerVector& servers, const D
ReadLock rl(&(d.second->d_lock));
const auto& server = d.second;
// we want to keep track of the last hash
if (max < *(server->hashes.rbegin())) {
max = *(server->hashes.rbegin());
last = server;
if (min > *(server->hashes.begin())) {
min = *(server->hashes.begin());
first = server;
}
auto hash_it = server->hashes.begin();
while (hash_it != server->hashes.end()
&& *hash_it < qhash) {
if (*hash_it > sel) {

auto hash_it = server->hashes.lower_bound(qhash);
if (hash_it != server->hashes.end()) {
if (*hash_it < sel) {
sel = *hash_it;
ret = server;
}
++hash_it;
}
}
}
}
if (ret != nullptr) {
return ret;
}
if (last != nullptr) {
return last;
if (first != nullptr) {
return first;
}
return shared_ptr<DownstreamState>();
}
Expand Down