Force mercury poll time to 1s (#12771)

core/services/ocr2/delegate.go

@@ -768,6 +768,11 @@ func (d *Delegate) newServicesMercury(
 		return nil, errors.New("could not coerce PluginProvider to MercuryProvider")
 	}
 
+	// HACK: We need fast config switchovers because they create downtime. This
+	// won't be properly resolved until we implement blue-green deploys:
+	// https://smartcontract-it.atlassian.net/browse/MERC-3386
+	lc.ContractConfigTrackerPollInterval = 1 * time.Second // Mercury requires a fast poll interval, this is the fastest that libocr supports. See: https://github.com/smartcontractkit/offchain-reporting/pull/520
+
 	oracleArgsNoPlugin := libocr2.MercuryOracleArgs{
 		BinaryNetworkEndpointFactory: d.peerWrapper.Peer2,
 		V2Bootstrappers:              bootstrapPeers,