Set active work to be not less than 2 and not more than input size

Values less than 2 are not accepted.

Input size constraint comes from our CI that is so slow, it cannot allow very large active work sizes

ipa-core/src/helpers/transport/query/mod.rs

@@ -1,6 +1,7 @@
 use std::{
+    cmp::{max, min},
     fmt::{Debug, Display, Formatter},
-    num::NonZeroU32,
+    num::{NonZeroU32, NonZeroUsize},
 };
 
 use serde::{Deserialize, Deserializer, Serialize};
@@ -140,9 +141,25 @@ impl RouteParams<RouteId, NoQueryId, NoStep> for &QueryConfig {
 }
 
 impl From<&QueryConfig> for GatewayConfig {
-    fn from(_value: &QueryConfig) -> Self {
-        // TODO: pick the correct value for active and test it
-        Self::default()
+    fn from(value: &QueryConfig) -> Self {
+        let mut config = Self::default();
+        // Minimum size for active work is 2 because:
+        // * `UnorderedReceiver` wants capacity to be greater than 1
+        // * 1 is better represented by not using seq_join and/or indeterminate total records
+        let active = max(
+            2,
+            min(
+                config.active.get(),
+                // It makes sense to start with active work set to input size, but some protocols
+                // may want to change that, if their fanout factor per input row is greater than 1.
+                // we don't have capabilities (see #ipa/1171) to allow that currently.
+                usize::try_from(value.size.0).expect("u32 fits into usize"),
+            ),
+        );
+        // we set active to be at least 2, so unwrap is fine.
+        config.active = NonZeroUsize::new(active).unwrap();
+
+        config
     }
 }