[keyserver] Filter fetchThreadInfos queries to only look at viewer's …

…threads

Summary:
This attempts strategy 3 outlined in [ENG-3877](https://linear.app/comm/issue/ENG-3877/avoid-global-fetchserverthreadinfos).

Depends on D8513

Test Plan:
I started this task by testing various queries in the production environment to check performance.

After implementing the change, I used this patch to check performance on the JS side in my dev environment, and to output raw queries so I could test their performance in production: https://gist.github.com/Ashoat/220bb35da34ac7820867ac874d87beab

I found that for all users other than me, this change significantly sped up `fetchThreadInfos`.

I then deployed this to production to test performance more reliably. Hopefully so far no issues!

Reviewers: tomek, atul

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D8514

keyserver/src/fetchers/thread-fetchers.js

@@ -24,6 +24,7 @@ import type { SQLStatementType } from '../database/types.js';
 import type { Viewer } from '../session/viewer.js';
 
 type FetchThreadInfosFilter = $Shape<{
+  +accessibleToUserID: string,
   +threadID: string,
   +threadIDs: $ReadOnlySet<string>,
   +parentThreadID: string,
@@ -32,13 +33,25 @@ type FetchThreadInfosFilter = $Shape<{
 function constructWhereClause(
   filter: FetchThreadInfosFilter,
 ): SQLStatementType {
+  const fromTable = filter.accessibleToUserID ? 'memberships' : 'threads';
+
   const conditions = [];
 
-  if (filter.threadID) {
+  if (filter.accessibleToUserID) {
+    conditions.push(
+      SQL`mm.user = ${filter.accessibleToUserID} AND mm.role > -1`,
+    );
+  }
+
+  if (filter.threadID && fromTable === 'memberships') {
+    conditions.push(SQL`mm.thread = ${filter.threadID}`);
+  } else if (filter.threadID) {
     conditions.push(SQL`t.id = ${filter.threadID}`);
   }
 
-  if (filter.threadIDs) {
+  if (filter.threadIDs && fromTable === 'memberships') {
+    conditions.push(SQL`mm.thread IN (${[...filter.threadIDs]})`);
+  } else if (filter.threadIDs) {
     conditions.push(SQL`t.id IN (${[...filter.threadIDs]})`);
   }
 
@@ -65,25 +78,46 @@ type FetchServerThreadInfosResult = {
 async function fetchServerThreadInfos(
   filter?: FetchThreadInfosFilter,
 ): Promise<FetchServerThreadInfosResult> {
+  let primaryFetchClause;
+  if (filter?.accessibleToUserID) {
+    primaryFetchClause = SQL`
+      FROM memberships mm
+      LEFT JOIN threads t ON t.id = mm.thread
+    `;
+  } else {
+    primaryFetchClause = SQL`
+      FROM threads t
+    `;
+  }
+
   const whereClause = filter ? constructWhereClause(filter) : '';
 
   const rolesQuery = SQL`
     SELECT t.id, t.default_role, r.id AS role, r.name, r.permissions
-    FROM threads t
-    LEFT JOIN roles r ON r.thread = t.id
-  `.append(whereClause);
+  `
+    .append(primaryFetchClause)
+    .append(
+      SQL`
+      LEFT JOIN roles r ON r.thread = t.id
+    `,
+    )
+    .append(whereClause);
 
   const threadsQuery = SQL`
-  SELECT t.id, t.name, t.parent_thread_id, t.containing_thread_id,
-    t.community, t.depth, t.color, t.description, t.type, t.creation_time,
-    t.source_message, t.replies_count, t.avatar, t.pinned_count, m.user, 
-    m.role, m.permissions, m.subscription, 
-    m.last_read_message < m.last_message AS unread, m.sender,
-    up.id AS upload_id, up.secret AS upload_secret
-  FROM threads t
-  LEFT JOIN memberships m ON m.thread = t.id AND m.role >= 0
-  LEFT JOIN uploads up ON up.container = t.id
+    SELECT t.id, t.name, t.parent_thread_id, t.containing_thread_id,
+      t.community, t.depth, t.color, t.description, t.type, t.creation_time,
+      t.source_message, t.replies_count, t.avatar, t.pinned_count, m.user,
+      m.role, m.permissions, m.subscription,
+      m.last_read_message < m.last_message AS unread, m.sender,
+      up.id AS upload_id, up.secret AS upload_secret
   `
+    .append(primaryFetchClause)
+    .append(
+      SQL`
+      LEFT JOIN memberships m ON m.thread = t.id AND m.role >= 0
+      LEFT JOIN uploads up ON up.container = t.id
+    `,
+    )
     .append(whereClause)
     .append(SQL` ORDER BY m.user ASC`);
   const [[threadsResult], [rolesResult]] = await Promise.all([
@@ -191,8 +225,12 @@ export type FetchThreadInfosResult = {
 
 async function fetchThreadInfos(
   viewer: Viewer,
-  filter?: FetchThreadInfosFilter,
+  inputFilter?: FetchThreadInfosFilter,
 ): Promise<FetchThreadInfosResult> {
+  const filter = {
+    accessibleToUserID: viewer.id,
+    ...inputFilter,
+  };
   const serverResult = await fetchServerThreadInfos(filter);
   return rawThreadInfosFromServerThreadInfos(viewer, serverResult);
 }