store: Reduce the amount of data getting mirrored from the primary

store/postgres/src/primary.rs

@@ -1583,19 +1583,25 @@ impl Mirror {
             "subgraph_version",
         ];
 
+        fn run_query(conn: &PgConnection, query: String) -> Result<(), StoreError> {
+            conn.batch_execute(&query).map_err(StoreError::from)
+        }
+
         fn copy_table(
             conn: &PgConnection,
             src_nsp: &str,
             dst_nsp: &str,
             table_name: &str,
         ) -> Result<(), StoreError> {
-            let query = format!(
-                "insert into {dst_nsp}.{table_name} select * from {src_nsp}.{table_name};",
-                src_nsp = src_nsp,
-                dst_nsp = dst_nsp,
-                table_name = table_name
-            );
-            conn.batch_execute(&query).map_err(StoreError::from)
+            run_query(
+                conn,
+                format!(
+                    "insert into {dst_nsp}.{table_name} select * from {src_nsp}.{table_name};",
+                    src_nsp = src_nsp,
+                    dst_nsp = dst_nsp,
+                    table_name = table_name
+                ),
+            )
         }
 
         let check_cancel = || {
@@ -1622,6 +1628,7 @@ impl Mirror {
         conn.batch_execute(&query)?;
         check_cancel()?;
 
+        // Repopulate `PUBLIC_TABLES` by copying their data wholesale
         for table_name in PUBLIC_TABLES {
             copy_table(
                 conn,
@@ -1631,15 +1638,30 @@ impl Mirror {
             )?;
             check_cancel()?;
         }
-        for table_name in SUBGRAPHS_TABLES {
-            copy_table(
-                conn,
-                &ForeignServer::metadata_schema(&*PRIMARY_SHARD),
-                NAMESPACE_SUBGRAPHS,
-                table_name,
-            )?;
-            check_cancel()?;
-        }
+
+        // Repopulate `SUBGRAPHS_TABLES` but only copy the data we actually
+        // need to respond to queries when the primary is down
+        let src_nsp = ForeignServer::metadata_schema(&*PRIMARY_SHARD);
+        let dst_nsp = NAMESPACE_SUBGRAPHS;
+
+        run_query(
+            conn,
+            format!(
+                "insert into {dst_nsp}.subgraph \
+                     select * from {src_nsp}.subgraph
+                     where current_version is not null;"
+            ),
+        )?;
+        run_query(
+            conn,
+            format!(
+                "insert into {dst_nsp}.subgraph_version \
+                 select v.* from {src_nsp}.subgraph_version v, {src_nsp}.subgraph s
+                  where v.id = s.current_version;"
+            ),
+        )?;
+        copy_table(conn, &src_nsp, dst_nsp, "subgraph_deployment_assignment")?;
+
         Ok(())
     }