Bug#20785598 USE ATOMICS TO AVOID MUTEX CONTENTION ON LOCK_PLUGIN DUE TO QUERY REWRITE FRAMEW

Use atomic counters when loading/unloading pre/post parse plugins.
Check counters in mysql_parse.

(cherry picked from commit 153316aaa82f8001ed7d52e4601e834993dad315)

Author: Tor Didriksen

sql/sql_parse.cc

@@ -5032,18 +5032,23 @@ void mysql_parse(THD *thd, Parser_state *parser_state)
   mysql_reset_thd_for_next_command(thd);
   lex_start(thd);
 
+  int32 num_preparse= my_atomic_load32(&num_pre_parse_plugins);
+  int32 num_postparse= my_atomic_load32(&num_post_parse_plugins);
+
   thd->m_parser_state= parser_state;
-  invoke_pre_parse_rewrite_plugins(thd);
+  if (num_preparse > 0)
+    invoke_pre_parse_rewrite_plugins(thd);
   thd->m_parser_state= NULL;
 
-  enable_digest_if_any_plugin_needs_it(thd, parser_state);
+  if (num_postparse > 0)
+    enable_digest_if_any_plugin_needs_it(thd, parser_state);
 
   if (query_cache.send_result_to_client(thd, thd->query()) <= 0)
   {
     LEX *lex= thd->lex;
 
     bool err= parse_sql(thd, parser_state, NULL);
-    if (!err)
+    if (num_postparse > 0 && !err)
       err= invoke_post_parse_rewrite_plugins(thd, false);
 
     const char *found_semicolon= parser_state->m_lip.found_semicolon;

sql/sql_plugin.cc

@@ -55,6 +55,9 @@ using std::max;
 static PSI_memory_key key_memory_plugin_ref;
 #endif
 
+volatile int32 num_pre_parse_plugins= 0;
+volatile int32 num_post_parse_plugins= 0;
+
 static PSI_memory_key key_memory_plugin_mem_root;
 static PSI_memory_key key_memory_plugin_init_tmp;
 static PSI_memory_key key_memory_plugin_int_mem_root;
@@ -955,6 +958,12 @@ static bool plugin_add(MEM_ROOT *tmp_root,
         {
           init_alloc_root(key_memory_plugin_int_mem_root,
                           &tmp_plugin_ptr->mem_root, 4096, 4096);
+
+          if (plugin->type == MYSQL_REWRITE_PRE_PARSE_PLUGIN)
+            my_atomic_add32(&num_pre_parse_plugins, 1);
+          if (plugin->type == MYSQL_REWRITE_POST_PARSE_PLUGIN)
+            my_atomic_add32(&num_post_parse_plugins, 1);
+
           DBUG_RETURN(FALSE);
         }
         tmp_plugin_ptr->state= PLUGIN_IS_FREED;
@@ -1029,6 +1038,12 @@ static void plugin_del(st_plugin_int *plugin)
   restore_pluginvar_names(plugin->system_vars);
   plugin_vars_free_values(plugin->system_vars);
   my_hash_delete(&plugin_hash[plugin->plugin->type], (uchar*)plugin);
+
+  if (plugin->plugin->type == MYSQL_REWRITE_PRE_PARSE_PLUGIN)
+    my_atomic_add32(&num_pre_parse_plugins, -1);
+  if (plugin->plugin->type == MYSQL_REWRITE_POST_PARSE_PLUGIN)
+    my_atomic_add32(&num_post_parse_plugins, -1);
+
   if (plugin->plugin_dl)
     plugin_dl_del(&plugin->plugin_dl->dl);
   plugin->state= PLUGIN_IS_FREED;

sql/sql_plugin.h

@@ -177,4 +177,8 @@ extern bool plugin_foreach_with_mask(THD *thd, plugin_foreach_func *func,
                                      int type, uint state_mask, void *arg);
 int lock_plugin_data();
 int unlock_plugin_data();
+
+extern volatile int32 num_pre_parse_plugins;
+extern volatile int32 num_post_parse_plugins;
+
 #endif

sql/sql_prepare.cc

@@ -106,7 +106,7 @@ When one supplies long data for a placeholder:
 #include "mysql/psi/mysql_ps.h" // MYSQL_EXECUTE_PS
 #include "binlog.h"
 #include "sql_audit.h"          // mysql_global_audit_mask
-
+#include "sql_plugin.h"
 
 #ifdef EMBEDDED_LIBRARY
 /* include MYSQL_BIND headers */
@@ -3281,7 +3281,10 @@ bool Prepared_statement::prepare(const char *packet, size_t packet_len)
   digest.reset(token_array, max_digest_length);
   thd->m_digest= &digest;
 
-  enable_digest_if_any_plugin_needs_it(thd, &parser_state);
+  int32 num_postparse= my_atomic_load32(&num_post_parse_plugins);
+
+  if (num_postparse > 0)
+    enable_digest_if_any_plugin_needs_it(thd, &parser_state);
 #ifndef EMBEDDED_LIBRARY
   if (is_any_audit_plugin_active(thd))
     parser_state.m_input.m_compute_digest= true;
@@ -3293,7 +3296,8 @@ bool Prepared_statement::prepare(const char *packet, size_t packet_len)
 
   if (!error)
   { // We've just created the statement maybe there is a rewrite
-    invoke_post_parse_rewrite_plugins(thd, true);
+    if (num_postparse > 0)
+      invoke_post_parse_rewrite_plugins(thd, true);
     error= init_param_array(this);
   }