Reduce WAL usage for transient feed data and no-op updates

CHANGELOG.md

@@ -6,6 +6,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [2.32.0] - Not released
+### Changed
+- Reduced PostgreSQL WAL generation by storing transient `local_bumps` feed-ordering
+  data in an unlogged table. Its contents can be cleared after an unclean PostgreSQL
+  shutdown and will repopulate through new activity.
+- Skipped physical `posts.feed_ids` updates when all requested feed IDs are already
+  present, avoiding unnecessary heap and index writes.
 
 ## [2.31.1] - 2026-08-03
 ### Added

app/support/DbAdapter/posts.js

@@ -182,10 +182,14 @@ const postsTrait = (superClass) =>
         return null;
       }
 
-      return this.database.raw('UPDATE posts SET feed_ids = (feed_ids | ?) WHERE uid = ?', [
-        feedIntIds,
-        postId,
-      ]);
+      // Updating feed_ids prevents HOT and rewrites every posts index.
+      // Skip physical no-op updates.
+      return this.database.raw(
+        `UPDATE posts
+         SET feed_ids = (feed_ids | ?)
+         WHERE uid = ? AND NOT (feed_ids @> ?::int[])`,
+        [feedIntIds, postId, feedIntIds],
+      );
     }
 
     withdrawPostFromFeeds(feedIntIds, postUUID) {

migrations/20260810123325_local_bumps_unlogged.ts

@@ -0,0 +1,7 @@
+import { type Knex } from 'knex';
+
+// local_bumps is disposable feed-ordering state that naturally repopulates after a crash.
+// Keep it unlogged to avoid WAL for its high-churn heap and indexes.
+export const up = (knex: Knex) => knex.schema.raw(`alter table local_bumps set unlogged`);
+
+export const down = (knex: Knex) => knex.schema.raw(`alter table local_bumps set logged`);

test/integration/support/DbAdapter/posts/feed-ids.js

@@ -0,0 +1,33 @@
+/* global $pg_database */
+import expect from 'unexpected';
+
+import cleanDB from '../../../../dbCleaner';
+import { dbAdapter, User } from '../../../../../app/models';
+
+describe('Post feed IDs', () => {
+  beforeEach(() => cleanDB($pg_database));
+
+  it('updates a post only when at least one feed ID is missing', async () => {
+    const luna = new User({ username: 'luna', password: 'password' });
+    await luna.create();
+
+    const post = await luna.newPost({ body: 'Post body' });
+    await post.create();
+
+    const likesFeedId = await luna.getLikesTimelineIntId();
+    const firstResult = await dbAdapter.insertPostIntoFeeds([likesFeedId], post.id);
+    const secondResult = await dbAdapter.insertPostIntoFeeds([likesFeedId], post.id);
+    const commentsFeedId = await luna.getCommentsTimelineIntId();
+    const partialResult = await dbAdapter.insertPostIntoFeeds(
+      [likesFeedId, commentsFeedId],
+      post.id,
+    );
+    const updatedPost = await dbAdapter.getPostById(post.id);
+
+    expect(firstResult.rowCount, 'to equal', 1);
+    expect(secondResult.rowCount, 'to equal', 0);
+    expect(partialResult.rowCount, 'to equal', 1);
+    expect(updatedPost.feedIntIds, 'to contain', likesFeedId);
+    expect(updatedPost.feedIntIds, 'to contain', commentsFeedId);
+  });
+});