Merge pull request #11668 from bharatnc/bnc/config-max-num-threads

max_thread_pool_size setting for changing max Threads in Global Thread Pool

docs/en/operations/server-configuration-parameters/settings.md

@@ -426,6 +426,18 @@ The value 0 means that you can delete all tables without any restrictions.
 <max_table_size_to_drop>0</max_table_size_to_drop>
 ```
 
+## max\_thread\_pool\_size {#max-thread-pool-size}
+
+The maximum number of threads in the Global Thread pool.
+
+Default value: 10000.
+
+**Example**
+
+``` xml
+<max_thread_pool_size>12000</max_thread_pool_size>
+```
+
 ## merge\_tree {#server_configuration_parameters-merge_tree}
 
 Fine tuning for tables in the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md).

programs/server/Server.cpp

@@ -431,6 +431,8 @@ int Server::main(const std::vector<std::string> & /*args*/)
     DateLUT::instance();
     LOG_TRACE(log, "Initialized DateLUT with time zone '{}'.", DateLUT::instance().getTimeZone());
 
+    /// Initialize global thread pool
+    GlobalThreadPool::initialize(config().getUInt("max_thread_pool_size", 10000));
 
     /// Storage with temporary data for processing of heavy queries.
     {

programs/server/config.xml

@@ -136,6 +136,15 @@
       -->
     <max_server_memory_usage>0</max_server_memory_usage>
 
+    <!-- Maximum number of threads in the Global thread pool.
+    This will default to a maximum of 10000 threads if not specified.
+    This setting will be useful in scenarios where there are a large number
+    of distributed queries that are running concurrently but are idling most
+    of the time, in which case a higher number of threads might be required.
+    -->
+
+     <max_thread_pool_size>10000</max_thread_pool_size>
+
     <!-- On memory constrained environments you may have to set this to value larger than 1.
       -->
     <max_server_memory_usage_to_ram_ratio>0.9</max_server_memory_usage_to_ram_ratio>

src/Common/ThreadPool.cpp

@@ -1,8 +1,11 @@
 #include <Common/ThreadPool.h>
 #include <Common/Exception.h>
 
+#include <cassert>
 #include <type_traits>
 
+#include <Poco/Util/Application.h>
+#include <Poco/Util/LayeredConfiguration.h>
 
 namespace DB
 {
@@ -261,9 +264,25 @@ void ThreadPoolImpl<Thread>::worker(typename std::list<Thread>::iterator thread_
 template class ThreadPoolImpl<std::thread>;
 template class ThreadPoolImpl<ThreadFromGlobalPool>;
 
+std::unique_ptr<GlobalThreadPool> GlobalThreadPool::the_instance;
+
+void GlobalThreadPool::initialize(size_t max_threads)
+{
+    assert(!the_instance);
+
+    the_instance.reset(new GlobalThreadPool(max_threads,
+        1000 /*max_free_threads*/, 10000 /*max_queue_size*/,
+        false /*shutdown_on_exception*/));
+}
 
 GlobalThreadPool & GlobalThreadPool::instance()
 {
-    static GlobalThreadPool ret;
-    return ret;
+    if (!the_instance)
+    {
+        // Allow implicit initialization. This is needed for old code that is
+        // impractical to redo now, especially Arcadia users and unit tests.
+        initialize();
+    }
+
+    return *the_instance;
 }

src/Common/ThreadPool.h

@@ -128,8 +128,16 @@ using FreeThreadPool = ThreadPoolImpl<std::thread>;
   */
 class GlobalThreadPool : public FreeThreadPool, private boost::noncopyable
 {
+    static std::unique_ptr<GlobalThreadPool> the_instance;
+
+    GlobalThreadPool(size_t max_threads_, size_t max_free_threads_,
+            size_t queue_size_, const bool shutdown_on_exception_)
+        : FreeThreadPool(max_threads_, max_free_threads_, queue_size_,
+            shutdown_on_exception_)
+    {}
+
 public:
-    GlobalThreadPool() : FreeThreadPool(10000, 1000, 10000, false) {}
+    static void initialize(size_t max_threads = 10000);
     static GlobalThreadPool & instance();
 };
 

tests/server-test.xml

@@ -17,6 +17,7 @@
     <https_port>58443</https_port>
     <tcp_port_secure>59440</tcp_port_secure>
     <interserver_http_port>59009</interserver_http_port>
+    <max_thread_pool_size>10000</max_thread_pool_size>
     <openSSL>
         <server> <!-- Used for https server AND secure tcp port -->
             <!-- openssl req -subj "/CN=localhost" -new -newkey rsa:2048 -days 365 -nodes -x509 -keyout /etc/clickhouse-server/server.key -out /etc/clickhouse-server/server.crt -->