Don't add index-site-members job if already queued.

queries/site_member.sql

@@ -3,3 +3,8 @@ INSERT INTO site_member (user_id, site_id, joined_at)
     VALUES (:user_id, :site_id, :joined_at)
     ON CONFLICT (user_id, site_id)
     DO NOTHING;
+
+-- :name get_site_member_job :one
+SELECT * FROM job
+    WHERE job_type = 'index-site-members'
+    AND data ->> 'site_slug' = :site_slug;

yellowstone/job/__init__.py

@@ -65,6 +65,12 @@ def index_site_members(self, data: SiteMemberJob) -> None:
         self.add_raw(JobType.INDEX_SITE_MEMBERS, cast(Json, data))
 
     def index_site_members_continue(self, site_slug: str) -> None:
+        # Only queue if there already isn't a member index job for the site
+        job = self.database.get_site_member_job(site_slug=site_slug)
+        if job is not None:
+            logger.debug("Found an index-site-members job for this site")
+            return
+
         # Reads the last member page, and continues from there
         offset = self.database.get_last_number_offset(site_slug=site_slug)
         self.index_site_members(