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db: fix UB in system.clients row sorting

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The comparator used to sort per-IP client rows was not a strict-weak-ordering (it could return true in both directions for some pairs), which makes `std::ranges::sort` behavior undefined. A concrete pair that breaks it (and is realistic in system.clients):
a = (port=9042, client_type="cql")
b = (port=10000, client_type="alternator")
With the current comparator:
cmp(a,b) = (9042 < 10000) || ("cql" < "alternator") = true || false = true
cmp(b,a) = (10000 < 9042) || ("alternator" < "cql") = false || true = true
So both directions are true, meaning there is no valid ordering that sort can achieve.

The fix is to sort lexicographically by (port, client_type) to match the table's clustering key and ensure deterministic ordering.

Closes scylladb/scylladb#28844
This commit is contained in:
Piotr Smaron
2026-03-02 10:08:22 +01:00
committed by Pavel Emelyanov
parent c331796d28
commit a31cb18324
1 changed files with 4 additions and 1 deletions
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5
db/virtual_tables.cc
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@@ -834,7 +834,10 @@ class clients_table : public streaming_virtual_table {
auto& clients = cd_map[dip.ip];
std::ranges::sort(clients, [] (const foreign_ptr<std::unique_ptr<client_data>>& a, const foreign_ptr<std::unique_ptr<client_data>>& b) {
return a->port < b->port || a->client_type_str() < b->client_type_str();
if (a->port != b->port) {
return a->port < b->port;
}
return a->client_type_str() < b->client_type_str();
});
for (const auto& cd : clients) {