Overlay: use restoreCache() timeout

src/overlay-database-utils.ts

@@ -158,7 +158,12 @@ function computeChangedFiles(
 // Constants for database caching
 const CACHE_VERSION = 1;
 const CACHE_PREFIX = "codeql-overlay-base-database";
-const MAX_CACHE_OPERATION_MS = 120_000; // Two minutes
+
+// The purpose of this ten-minute limit is to guard against the possibility
+// that the cache service is unresponsive, which would otherwise cause the
+// entire action to hang.  Normally we expect cache operations to complete
+// within two minutes.
+const MAX_CACHE_OPERATION_MS = 600_000;
 
 /**
  * Checks that the overlay-base database is valid by checking for the
@@ -351,8 +356,38 @@ export async function downloadOverlayBaseDatabaseFromCache(
   try {
     const databaseDownloadStart = performance.now();
     const foundKey = await waitForResultWithTimeLimit(
+      // This ten-minute limit for the cache restore operation is mainly to
+      // guard against the possibility that the cache service is unresponsive
+      // and hangs outside the data download.
+      //
+      // Data download (which is normally the most time-consuming part of the
+      // restore operation) should not run long enough to hit this limit. Even
+      // for an extremely large 10GB database, at a download speed of 40MB/s
+      // (see below), the download should complete within five minutes. If we
+      // do hit this limit, there are likely more serious problems other than
+      // mere slow download speed.
+      //
+      // This is important because we don't want any ongoing file operations
+      // on the database directory when we do hit this limit. Hitting this
+      // time limit takes us to a fallback path where we re-initialize the
+      // database from scratch at dbLocation, and having the cache restore
+      // operation continue to write into dbLocation in the background would
+      // really mess things up. We want to hit this limit only in the case
+      // of a hung cache service, not just slow download speed.
       MAX_CACHE_OPERATION_MS,
-      actionsCache.restoreCache([dbLocation], cacheRestoreKeyPrefix),
+      actionsCache.restoreCache(
+        [dbLocation],
+        cacheRestoreKeyPrefix,
+        undefined,
+        {
+          // Azure SDK download (which is the default) uses 128MB segments; see
+          // https://github.com/actions/toolkit/blob/main/packages/cache/README.md.
+          // Setting segmentTimeoutInMs to 3000 translates to segment download
+          // speed of about 40 MB/s, which should be achievable unless the
+          // download is unreliable (in which case we do want to abort).
+          segmentTimeoutInMs: 3000,
+        },
+      ),
       () => {
         logger.info("Timed out downloading overlay-base database from cache");
       },