SERVER-29465 Add warning about Windows SystemFileCacheSize for WiredTiger

1 files changed, 17 insertions, 0 deletions

diff --git a/src/mongo/db/startup_warnings_mongod.cpp b/src/mongo/db/startup_warnings_mongod.cpp
index a15bf056428..6f0c42263f3 100644
--- a/src/mongo/db/startup_warnings_mongod.cpp
+++ b/src/mongo/db/startup_warnings_mongod.cpp
@@ -369,6 +369,23 @@ void logMongodStartupWarnings(const StorageGlobalParams& storageParams,
         warned = true;
     }
 
+    if (storageParams.engine == "wiredTiger") {
+        // If the filesystemMaxCacheSize / totalMemorySize > 0.4, we should raise this
+        // warning because it leads to terrible performance for WiredTiger
+        const double filesystemCachePercentageThreshold = 0.4;
+        if (p.getMaxSystemFileCachePercentage() > filesystemCachePercentageThreshold) {
+            log() << startupWarningsLog;
+            log()
+                << "** WARNING: The file system cache of this machine is configured to be greater "
+                << "than " << 100 * filesystemCachePercentageThreshold << "% of the total memory. "
+                << "This can lead to increased memory pressure and poor performance."
+                << startupWarningsLog;
+            log() << "See http://dochub.mongodb.org/core/wt-windows-system-file-cache"
+                  << startupWarningsLog;
+            warned = true;
+        }
+    }
+
 #endif  // #ifdef _WIN32
 
     if (storageParams.engine == "ephemeralForTest") {