replicators: Move version query before ddl setup

If we are connecting to postgres 13, the ddl setup commands we run cause
our connection to be considered a "replication connection", which if the
upstream is configured in a certain way (in a way that Aurora Postgres
is configured), would cause the query for the server version to fail.

Moving the query to before the ddl setup allows the query to succeed.

Release-Note-Core: Fixed a bug that would cause replication to fail on
  Aurora Postgres version 13 databases.
Refs: ENG-2208
Change-Id: Ie3f506e593c9bbd11802852472b0d29cbc5b0671
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/4015
Tested-by: Buildkite CI
Reviewed-by: Sif Hall <[email protected]>

Author: lukoktonos

replicators/src/noria_adapter.rs

@@ -411,6 +411,26 @@ impl NoriaAdapter {
             None,
         )?;
 
+        // For Postgres 13, once we setup ddl replication, the following query can be rejected, so
+        // run it ahead of time.
+        // TODO: (luke): We can probably consolidate this query with the db_version string query
+        // below
+        let version_num: u32 = {
+            let (client, connection) = pgsql_opts.connect(tls_connector.clone()).await?;
+            let _connection_handle = tokio::spawn(connection);
+            client
+                .query_one("SHOW server_version_num", &[])
+                .await
+                .and_then(|row| row.try_get::<_, String>(0))
+                .map_err(|e| {
+                    ReadySetError::Internal(format!("Unable to determine postgres version: {}", e))
+                })?
+                .parse()
+                .map_err(|e| {
+                    ReadySetError::Internal(format!("Unable to parse postgres version: {}", e))
+                })?
+        };
+
         let mut connector = Box::new(
             PostgresWalConnector::connect(
                 pgsql_opts.clone(),
@@ -451,7 +471,7 @@ impl NoriaAdapter {
             let snapshot_start = Instant::now();
             // If snapshot name exists, it means we need to make a snapshot to noria
 
-            let (mut client, connection) = pgsql_opts.connect(tls_connector).await?;
+            let (mut client, connection) = pgsql_opts.connect(tls_connector.clone()).await?;
 
             let connection_handle = tokio::spawn(connection);
             let db_version = client
@@ -504,7 +524,7 @@ impl NoriaAdapter {
         }
 
         connector
-            .start_replication(REPLICATION_SLOT, PUBLICATION_NAME)
+            .start_replication(REPLICATION_SLOT, PUBLICATION_NAME, version_num)
             .await?;
 
         let replication_offsets = noria.replication_offsets().await?;

replicators/src/postgres_connector/connector.rs

@@ -260,15 +260,8 @@ impl PostgresWalConnector {
         &mut self,
         slot: &str,
         publication: &str,
+        version: u32,
     ) -> ReadySetResult<()> {
-        let version: u32 = self
-            .one_row_query("SHOW server_version_num", 1)
-            .await?
-            .get(0)
-            .unwrap()
-            .parse()
-            .unwrap_or(0);
-
         let inner_client = self.client.inner();
         let wal_position = self.next_position.unwrap_or_default();
         let messages_support = if version >= 140000 {