SERVER-23391 Lower WiredTiger cache size floor

4 files changed, 26 insertions, 17 deletions

diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_init.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_init.cpp
index 5ccc1093549..783983aa93b 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_init.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_init.cpp
@@ -61,25 +61,12 @@ public:
             warning() << "Recovering data from the last clean checkpoint.";
         }
 
-        size_t cacheSizeGB = wiredTigerGlobalOptions.cacheSizeGB;
-        if (cacheSizeGB == 0) {
-            // Since the user didn't provide a cache size, choose a reasonable default value.
-            // We want to reserve 1GB for the system and binaries, but it's not bad to
-            // leave a fair amount left over for pagecache since that's compressed storage.
-            ProcessInfo pi;
-            double memSizeMB = pi.getMemSizeMB();
-            if (memSizeMB > 0) {
-                double cacheMB = (memSizeMB - 1024) * 0.6;
-                cacheSizeGB = static_cast<size_t>(cacheMB / 1024);
-                if (cacheSizeGB < 1)
-                    cacheSizeGB = 1;
-            }
-        }
+        size_t cacheMB = WiredTigerUtil::getCacheSizeMB(wiredTigerGlobalOptions.cacheSizeGB);
         const bool ephemeral = false;
         WiredTigerKVEngine* kv = new WiredTigerKVEngine(getCanonicalName().toString(),
                                                         params.dbpath,
                                                         wiredTigerGlobalOptions.engineConfig,
-                                                        cacheSizeGB,
+                                                        cacheMB,
                                                         params.dur,
                                                         ephemeral,
                                                         params.repair,
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
index 51749294c3d..d8547c421f9 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
@@ -171,7 +171,7 @@ TicketServerParameter openReadTransactionParam(&openReadTransaction,
 WiredTigerKVEngine::WiredTigerKVEngine(const std::string& canonicalName,
                                        const std::string& path,
                                        const std::string& extraOpenOptions,
-                                       size_t cacheSizeGB,
+                                       size_t cacheSizeMB,
                                        bool durable,
                                        bool ephemeral,
                                        bool repair,
@@ -200,7 +200,7 @@ WiredTigerKVEngine::WiredTigerKVEngine(const std::string& canonicalName,
 
     std::stringstream ss;
     ss << "create,";
-    ss << "cache_size=" << cacheSizeGB << "G,";
+    ss << "cache_size=" << cacheSizeMB << "M,";
     ss << "session_max=20000,";
     ss << "eviction=(threads_max=4),";
     ss << "config_base=false,";
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_util.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_util.cpp
index ef81ff1acc3..c747087fbf8 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_util.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_util.cpp
@@ -45,6 +45,7 @@
 #include "mongo/util/assert_util.h"
 #include "mongo/util/log.h"
 #include "mongo/util/mongoutils/str.h"
+#include "mongo/util/processinfo.h"
 #include "mongo/util/scopeguard.h"
 
 namespace mongo {
@@ -317,6 +318,20 @@ int64_t WiredTigerUtil::getIdentSize(WT_SESSION* s, const std::string& uri) {
     return result.getValue();
 }
 
+size_t WiredTigerUtil::getCacheSizeMB(int requestedCacheSizeGB) {
+    double cacheSizeMB;
+    if (requestedCacheSizeGB == 0) {
+        // Choose a reasonable amount of cache when not explicitly specified by user.
+        // Set a minimum of 256MB, otherwise use 60% of available memory over 1GB.
+        ProcessInfo pi;
+        double memSizeMB = pi.getMemSizeMB();
+        cacheSizeMB = std::max((memSizeMB - 1024) * 0.6, 256.0);
+    } else {
+        cacheSizeMB = 1024 * requestedCacheSizeGB;
+    }
+    return static_cast<size_t>(cacheSizeMB);
+}
+
 namespace {
 int mdb_handle_error(WT_EVENT_HANDLER* handler,
                      WT_SESSION* session,
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_util.h b/src/mongo/db/storage/wiredtiger/wiredtiger_util.h
index af8b6ee1af2..6f12bd54531 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_util.h
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_util.h
@@ -175,6 +175,13 @@ public:
 
     static int64_t getIdentSize(WT_SESSION* s, const std::string& uri);
 
+
+    /**
+     * Return amount of memory to use for the WiredTiger cache based on either the startup
+     * option chosen or the amount of available memory on the host.
+     */
+    static size_t getCacheSizeMB(int requestedCacheSizeGB);
+
     /**
      * Returns a WT_EVENT_HANDER with MongoDB's default handlers.
      * The default handlers just log so it is recommended that you consider calling them even if