Reduce default CDC queue size

cpp/cdc/CDC.hpp

@@ -16,8 +16,9 @@ struct CDCOptions {
     Duration shardTimeout = 100_ms;
     bool xmon = false;
     bool xmonProd = false;
-    // at 1ms per request it's 10 seconds worth of requests.
-    uint64_t maximumEnqueuedRequests = 10000;
+    // currently the maximum CDC throughput is roughly 200req/s, and the max timeout is 2sec,
+    // so storing a maximum of 5sec worth of requests seems like a decent compromise.
+    uint64_t maximumEnqueuedRequests = 1000;
     bool metrics = false;
 };