Report an error if jemalloc.background_thread was requested

programs/server/CMakeLists.txt

@@ -19,6 +19,7 @@ set (CLICKHOUSE_SERVER_LINK
         clickhouse_storages_system
         clickhouse_table_functions
         string_utils
+        jemalloc
 
     ${LINK_RESOURCE_LIB}
 

programs/server/Server.cpp

@@ -101,6 +101,10 @@
 #   include <Server/KeeperTCPHandlerFactory.h>
 #endif
 
+#if USE_JEMALLOC
+#    include <jemalloc/jemalloc.h>
+#endif
+
 namespace CurrentMetrics
 {
     extern const Metric Revision;
@@ -109,11 +113,35 @@ namespace CurrentMetrics
     extern const Metric MaxDDLEntryID;
 }
 
+#if USE_JEMALLOC
+static bool jemallocOptionEnabled(const char *name)
+{
+    bool value;
+    size_t size = sizeof(value);
+
+    if (mallctl(name, reinterpret_cast<void *>(&value), &size, /* newp= */ nullptr, /* newlen= */ 0))
+        throw Poco::SystemException("mallctl() failed");
+
+    return value;
+}
+#else
+static bool jemallocOptionEnabled(const char *) { return 0; }
+#endif
+
 
 int mainEntryClickHouseServer(int argc, char ** argv)
 {
     DB::Server app;
 
+    if (jemallocOptionEnabled("opt.background_thread"))
+    {
+        LOG_ERROR(&app.logger(),
+            "jemalloc.background_thread was requested, "
+            "however ClickHouse uses percpu_arena and background_thread most likely will not give any benefits, "
+            "and also background_thread is not compatible with ClickHouse watchdog "
+            "(that can be disabled with CLICKHOUSE_WATCHDOG_ENABLE=0)");
+    }
+
     /// Do not fork separate process from watchdog if we attached to terminal.
     /// Otherwise it breaks gdb usage.
     /// Can be overridden by environment variable (cannot use server config at this moment).