Fix Posts List Performance + cursor-based pagination

crates/api_common/src/post.rs

@@ -5,7 +5,7 @@ use lemmy_db_schema::{
   PostFeatureType,
   SortType,
 };
-use lemmy_db_views::structs::{PostReportView, PostView};
+use lemmy_db_views::structs::{PaginationCursor, PostReportView, PostView};
 use lemmy_db_views_actor::structs::{CommunityModeratorView, CommunityView};
 use serde::{Deserialize, Serialize};
 use serde_with::skip_serializing_none;
@@ -70,6 +70,7 @@ pub struct GetPostResponse {
 pub struct GetPosts {
   pub type_: Option<ListingType>,
   pub sort: Option<SortType>,
+  /// DEPRECATED, use page_cursor
   pub page: Option<i64>,
   pub limit: Option<i64>,
   pub community_id: Option<CommunityId>,
@@ -78,6 +79,7 @@ pub struct GetPosts {
   pub liked_only: Option<bool>,
   pub disliked_only: Option<bool>,
   pub auth: Option<Sensitive<String>>,
+  pub page_cursor: Option<PaginationCursor>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone)]
@@ -86,6 +88,8 @@ pub struct GetPosts {
 /// The post list response.
 pub struct GetPostsResponse {
   pub posts: Vec<PostView>,
+  /// the pagination cursor to use to fetch the next page
+  pub next_page: Option<PaginationCursor>,
 }
 
 #[derive(Debug, Serialize, Deserialize, Clone, Default)]

crates/apub/src/api/list_posts.rs

@@ -11,7 +11,10 @@ use lemmy_api_common::{
   utils::{check_private_instance, local_user_view_from_jwt_opt_new},
 };
 use lemmy_db_schema::source::{community::Community, local_site::LocalSite};
-use lemmy_db_views::{post_view::PostQuery, structs::LocalUserView};
+use lemmy_db_views::{
+  post_view::PostQuery,
+  structs::{LocalUserView, PaginationCursor},
+};
 use lemmy_utils::error::{LemmyError, LemmyErrorExt, LemmyErrorType};
 
 #[tracing::instrument(skip(context))]
@@ -48,6 +51,12 @@ pub async fn list_posts(
     &local_site,
     community_id,
   )?);
+  // parse pagination token
+  let page_after = if let Some(pa) = &data.page_cursor {
+    Some(pa.read(&mut context.pool()).await?)
+  } else {
+    None
+  };
 
   let posts = PostQuery {
     local_user: local_user_view.as_ref(),
@@ -58,12 +67,15 @@ pub async fn list_posts(
     liked_only,
     disliked_only,
     page,
+    page_after,
     limit,
     ..Default::default()
   }
   .list(&mut context.pool())
   .await
   .with_lemmy_type(LemmyErrorType::CouldntGetPosts)?;
 
-  Ok(Json(GetPostsResponse { posts }))
+  // if this page wasn't empty, then there is a next page after the last post on this page
+  let next_page = posts.last().map(PaginationCursor::after_post);
+  Ok(Json(GetPostsResponse { posts, next_page }))
 }