From c9ba2ac0251ae3a9dda1371222a2d5023043b37a Mon Sep 17 00:00:00 2001
From: Jakob Ackermann <jakob.ackermann@overleaf.com>
Date: Fri, 20 Mar 2026 12:07:47 +0100
Subject: [PATCH] [web] enable clsi-cache for all compiles for 20min during
 outages (#32337)

* [web] enable clsi-cache for all compiles for 20min during outages

* [web] populate clsi-cache when compile from history is enabled

* [web] hide history snapshot from frontend

GitOrigin-RevId: e46c8b5ab401ebdc2407e44eb95439e4d43400da
---
 .../src/Features/Compile/ClsiCacheManager.mjs |  3 ++-
 .../app/src/Features/Compile/ClsiManager.mjs  | 19 +++++++++++++++++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/services/web/app/src/Features/Compile/ClsiCacheManager.mjs b/services/web/app/src/Features/Compile/ClsiCacheManager.mjs
index aba619dae3..de78c0edc4 100644
--- a/services/web/app/src/Features/Compile/ClsiCacheManager.mjs
+++ b/services/web/app/src/Features/Compile/ClsiCacheManager.mjs
@@ -62,7 +62,8 @@ async function getLatestBuildFromCache(projectId, userId, filename, signal) {
       isUpToDate,
       lastUpdated,
       size,
-      allFiles,
+      // Hide history snapshot from frontend
+      allFiles: allFiles.filter(f => f !== 'history-resync.json.gz'),
       shard,
       zone,
     },
diff --git a/services/web/app/src/Features/Compile/ClsiManager.mjs b/services/web/app/src/Features/Compile/ClsiManager.mjs
index 5da6c55c39..4d995208d9 100644
--- a/services/web/app/src/Features/Compile/ClsiManager.mjs
+++ b/services/web/app/src/Features/Compile/ClsiManager.mjs
@@ -42,6 +42,10 @@ const CLSI_COOKIES_ENABLED = (Settings.clsiCookie?.key ?? '') !== ''
 // The timeout in services/clsi/app.js is 10 minutes, so we'll be on the safe side with 12 minutes
 const COMPILE_REQUEST_TIMEOUT_MS = 12 * 60 * 1000
 
+// Enable clsi-cache for all compiles for 20min when detecting low capacity.
+const ENABLE_COMPILE_FROM_CACHE_ON_503_MS = 20 * 60 * 1000
+let enableCompileFromCacheUntil = 0
+
 function _baseHistoryVersionKey(projectId, userId) {
   return `baseHistoryVersion:${projectId}:${userId}`
 }
@@ -678,6 +682,8 @@ async function _postToClsi(
       } else if (err.response.status === 423) {
         return { response: { compile: { status: 'compile-in-progress' } } }
       } else if (err.response.status === 503) {
+        enableCompileFromCacheUntil =
+          Date.now() + ENABLE_COMPILE_FROM_CACHE_ON_503_MS
         return { response: { compile: { status: 'unavailable' } } }
       } else if (err.response.status === 504) {
         return { response: { compile: { status: 'timedout' } } }
@@ -1104,11 +1110,20 @@ function _finaliseRequest(projectId, options, project, docs, files) {
         compileGroup: options.compileGroup,
         // Overleaf alpha/staff users get compileGroup=alpha (via getProjectCompileLimits in CompileManager), enroll them into the premium rollout of clsi-cache.
         compileFromClsiCache:
-          ['alpha', 'priority'].includes(options.compileGroup) &&
+          // enable for premium compiles
+          (['alpha', 'priority'].includes(options.compileGroup) ||
+            // enable for free for short period when we saw low capacity
+            enableCompileFromCacheUntil > Date.now()) &&
           options.compileFromClsiCache,
         populateClsiCache:
+          // enable for premium compiles
           (['alpha', 'priority'].includes(options.compileGroup) ||
-            options.metricsPath === 'clsi-cache-template') &&
+            // enable when populating template cache
+            options.metricsPath === 'clsi-cache-template' ||
+            // populate indefinitely for free when we saw low capacity
+            !!enableCompileFromCacheUntil ||
+            // populate with compile from history enabled to re-use snapshot from cache
+            !!options.rawChangeOperations) &&
           options.populateClsiCache,
         enablePdfCaching:
           (Settings.enablePdfCaching && options.enablePdfCaching) || false,