MWL#182: Explain running statements: address review feedback

- switch SHOW EXPLAIN to using an INFORMATION_SCHEMA table.

mysql-test/r/show_explain.result

@@ -798,7 +798,7 @@ pk	data
 20	data1
 set autocommit=0;
 select * from t1 where pk between 10 and 20 for update;
-show explain for 3;
+# do: send_eval show explain for 3;
 kill query $thr_default;
 ERROR 70100: Query execution was interrupted
 rollback;
@@ -816,3 +816,8 @@ pk	data
 20	data1
 drop table t1;
 drop table t0;
+# 
+# Check that the I_S table is invisible
+# 
+select table_name from information_schema.tables where table_schema='information_schema' and table_name like '%explain%';
+table_name

mysql-test/t/show_explain.test

@@ -818,7 +818,10 @@ connection default;
 let $wait_condition= select State='Sending data' from information_schema.processlist where id=$thr2;
 let $thr_default=`select connection_id()`;
 --source include/wait_condition.inc
+--echo # do: send_eval show explain for $thr2;
+--disable_query_log
 send_eval show explain for $thr2;
+--enable_query_log
 
 # kill the SHOW EXPLAIN command
 connection con3;
@@ -844,3 +847,9 @@ disconnect con2;
 ##       thread and served together.
 
 drop table t0;
+
+--echo # 
+--echo # Check that the I_S table is invisible
+--echo # 
+select table_name from information_schema.tables where table_schema='information_schema' and table_name like '%explain%';
+

sql/handler.h

@@ -600,6 +600,7 @@ enum enum_schema_tables
   SCH_COLUMN_PRIVILEGES,
   SCH_ENGINES,
   SCH_EVENTS,
+  SCH_EXPLAIN,
   SCH_FILES,
   SCH_GLOBAL_STATUS,
   SCH_GLOBAL_VARIABLES,

sql/my_apc.cc

@@ -24,7 +24,35 @@
 
 /* For standalone testing of APC system, see unittest/sql/my_apc-t.cc */
 
+#ifndef MY_APC_STANDALONE
+
+ST_FIELD_INFO show_explain_fields_info[]=
+{
+  /* field_name, length, type, value, field_flags, old_name*/
+  {"id", 3, MYSQL_TYPE_LONGLONG, 0 /*value*/, MY_I_S_MAYBE_NULL, "id", 
+    SKIP_OPEN_TABLE},
+  {"select_type", 19, MYSQL_TYPE_STRING, 0 /*value*/, 0, "select_type", 
+    SKIP_OPEN_TABLE},
+  {"table", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0 /*value*/, MY_I_S_MAYBE_NULL,
+   "table", SKIP_OPEN_TABLE},
+  {"type", 10, MYSQL_TYPE_STRING, 0, MY_I_S_MAYBE_NULL, "type", SKIP_OPEN_TABLE},
+  {"possible_keys", NAME_CHAR_LEN*MAX_KEY, MYSQL_TYPE_STRING, 0/*value*/,
+    MY_I_S_MAYBE_NULL, "possible_keys", SKIP_OPEN_TABLE},
+  {"key", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0/*value*/, MY_I_S_MAYBE_NULL, 
+   "key", SKIP_OPEN_TABLE},
+  {"key_len", NAME_CHAR_LEN*MAX_KEY, MYSQL_TYPE_STRING, 0/*value*/, 
+    MY_I_S_MAYBE_NULL, "key_len", SKIP_OPEN_TABLE},
+  {"ref", NAME_CHAR_LEN*MAX_REF_PARTS, MYSQL_TYPE_STRING, 0/*value*/,
+    MY_I_S_MAYBE_NULL, "ref", SKIP_OPEN_TABLE},
+  {"rows", 10, MYSQL_TYPE_LONGLONG, 0/*value*/, MY_I_S_MAYBE_NULL, "rows", 
+    SKIP_OPEN_TABLE},
+  {"Extra", 255, MYSQL_TYPE_STRING, 0/*value*/, 0 /*flags*/, "Extra", 
+    SKIP_OPEN_TABLE},
+  {0, 0, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE}
+};
+
 
+#endif
 /* 
   Initialize the target. 
    

sql/protocol.h

@@ -78,20 +78,6 @@ public:
   virtual bool send_result_set_metadata(List<Item> *list, uint flags);
   bool send_result_set_row(List<Item> *row_items);
 
-  void get_packet(const char **start, size_t *length) 
-  {
-    *start= packet->ptr();
-    *length= packet->length(); 
-  }
-  void set_packet(const char *start, size_t len)
-  {
-    packet->length(0);
-    packet->append(start, len);
-#ifndef DBUG_OFF
-  field_pos= field_count - 1;
-#endif
-  }
-
   bool store(I_List<i_string> *str_list);
   bool store(const char *from, CHARSET_INFO *cs);
   String *storage_packet() { return packet; }

sql/sql_class.cc

@@ -2309,89 +2309,15 @@ int select_send::send_data(List<Item> &items)
   DBUG_RETURN(0);
 }
 
-//////////////////////////////////////////////////////////////////////////////
-
-/*
-  Save the data being sent in our internal buffer.
-*/
 
 int select_result_explain_buffer::send_data(List<Item> &items)
 {
-  List_iterator_fast<Item> li(items);
-  char buff[MAX_FIELD_WIDTH];
-  String buffer(buff, sizeof(buff), &my_charset_bin);
-  DBUG_ENTER("select_send::send_data");
-
-  protocol->prepare_for_resend();
-  Item *item;
-  while ((item=li++))
-  {
-    if (item->send(protocol, &buffer))
-    {
-      protocol->free();				// Free used buffer
-      my_message(ER_OUT_OF_RESOURCES, ER(ER_OUT_OF_RESOURCES), MYF(0));
-      break;
-    }
-    /*
-      Reset buffer to its original state, as it may have been altered in
-      Item::send().
-    */
-    buffer.set(buff, sizeof(buff), &my_charset_bin);
-  }
-
-  if (thd->is_error())
-  {
-    protocol->remove_last_row();
-    DBUG_RETURN(1);
-  }
-  /* 
-    Instead of calling protocol->write(), steal the packed and put it to our
-    buffer 
-  */
-  const char *packet_data;
-  size_t len;
-  protocol->get_packet(&packet_data, &len);
-
-  String *s= new (thd->mem_root) String;
-  s->append(packet_data, len);
-  data_rows.push_back(s);
-  protocol->remove_last_row(); // <-- this does nothing. Do we need it?
-                               // prepare_for_resend() will wipe out the packet
-  DBUG_RETURN(0);
-}
-
-
-/* Write the saved resultset to the client (via this->protocol) and free it. */
-
-void select_result_explain_buffer::flush_data()
-{
-  List_iterator<String> it(data_rows);
-  String *str;
-  while ((str= it++))
-  {
-    protocol->set_packet(str->ptr(), str->length());
-    protocol->write();
-    delete str;
-  }
-  data_rows.empty();
-}
-
-
-/* Free the accumulated resultset */
-
-void select_result_explain_buffer::discard_data()
-{
-  List_iterator<String> it(data_rows);
-  String *str;
-  while ((str= it++))
-  {
-    delete str;
-  }
-  data_rows.empty();
+  fill_record(thd, dst_table->field, items, TRUE, FALSE);
+  if ((dst_table->file->ha_write_tmp_row(dst_table->record[0])))
+    return 1;
+  return 0;
 }
 
-//////////////////////////////////////////////////////////////////////////////
-
 
 bool select_send::send_eof()
 {

sql/sql_class.h

@@ -3319,32 +3319,27 @@ public:
 
 
 /*
-  A select result sink that collects the sent data and then can flush it to
-  network when requested.
+  This is a select_result_sink which simply writes all data into a (temporary)
+  table. Creation/deletion of the table is outside of the scope of the class
   
-  This class is targeted at collecting EXPLAIN output:
-  - Unoptimized data storage (can't handle big datasets)
+  It is aimed at capturing SHOW EXPLAIN output, so:
   - Unlike select_result class, we don't assume that the sent data is an 
     output of a SELECT_LEX_UNIT (and so we dont apply "LIMIT x,y" from the
     unit)
+  - We don't try to convert the target table to MyISAM 
 */
 
 class select_result_explain_buffer : public select_result_sink
 {
 public:
+  select_result_explain_buffer(THD *thd_arg, TABLE *table_arg) : 
+    thd(thd_arg), dst_table(table_arg) {};
+
   THD *thd;
-  Protocol *protocol;
-  select_result_explain_buffer(){};
+  TABLE *dst_table; /* table to write into */
 
   /* The following is called in the child thread: */
   int send_data(List<Item> &items);
-
-  /* this will be called in the parent thread: */
-  void flush_data();
-
-  void discard_data();
-
-  List<String> data_rows;
 };
 
 

sql/sql_lex.h

@@ -2357,7 +2357,8 @@ struct LEX: public Query_tables_list
   char *backup_dir;				/* For RESTORE/BACKUP */
   char* to_log;                                 /* For PURGE MASTER LOGS TO */
   char* x509_subject,*x509_issuer,*ssl_cipher;
-  String *wild;
+  String *wild; /* Wildcard in SHOW {something} LIKE 'wild'*/ 
+  Item *show_explain_for_thread; /* id in SHOW EXPLAIN FOR id */
   sql_exchange *exchange;
   select_result *result;
   Item *default_value, *on_update_value;

sql/sql_parse.cc

@@ -2144,6 +2144,32 @@ mysql_execute_command(THD *thd)
     execute_show_status(thd, all_tables);
     break;
   }
+  case SQLCOM_SHOW_EXPLAIN:
+  {
+    if (!thd->security_ctx->priv_user[0] &&
+        check_global_access(thd,PROCESS_ACL))
+      break;
+
+    /*
+      The select should use only one table, it's the SHOW EXPLAIN pseudo-table
+    */
+    if (lex->sroutines.records || lex->query_tables->next_global)
+    {
+      my_error(ER_NOT_SUPPORTED_YET, MYF(0), "Usage of subqueries or stored "
+               "function calls as part of this statement");
+      break;
+    }
+
+    Item **it= &(lex->show_explain_for_thread);
+    if ((!(*it)->fixed && (*it)->fix_fields(lex->thd, it)) || 
+        (*it)->check_cols(1))
+    {
+      my_message(ER_SET_CONSTANTS_ONLY, ER(ER_SET_CONSTANTS_ONLY),
+		 MYF(0));
+      goto error;
+    }
+    /* no break; fall through */
+  }
   case SQLCOM_SHOW_DATABASES:
   case SQLCOM_SHOW_TABLES:
   case SQLCOM_SHOW_TRIGGERS:
@@ -3128,35 +3154,6 @@ end_with_restore_list:
                            thd->security_ctx->priv_user),
                           lex->verbose);
     break;
-  case SQLCOM_SHOW_EXPLAIN:
-  {
-    const char *effective_user;
-    /* Same security as SHOW PROCESSLIST (TODO check this) */
-    if (!thd->security_ctx->priv_user[0] &&
-        check_global_access(thd,PROCESS_ACL))
-      break;
-
-    Item *it= (Item *)lex->value_list.head();
-
-    if (lex->table_or_sp_used())
-    {
-      my_error(ER_NOT_SUPPORTED_YET, MYF(0), "Usage of subqueries or stored "
-               "function calls as part of this statement");
-      break;
-    }
-
-    if ((!it->fixed && it->fix_fields(lex->thd, &it)) || it->check_cols(1))
-    {
-      my_message(ER_SET_CONSTANTS_ONLY, ER(ER_SET_CONSTANTS_ONLY),
-		 MYF(0));
-      goto error;
-    }
-    effective_user=(thd->security_ctx->master_access & PROCESS_ACL ?  NullS :
-                     thd->security_ctx->priv_user);
-
-    mysqld_show_explain(thd, effective_user, (ulong)it->val_int());
-    break;
-  }
   case SQLCOM_SHOW_AUTHORS:
     res= mysqld_show_authors(thd);
     break;

sql/sql_show.cc

@@ -1999,32 +1999,24 @@ void mysqld_list_processes(THD *thd,const char *user, bool verbose)
 }
 
 
-/*
-  SHOW EXPLAIN FOR command handler
-
-  @param  thd          Current thread's thd
-  @param  calling_user User that invoked SHOW EXPLAIN, or NULL if the user 
-                       has SUPER or PROCESS privileges, and so is allowed
-                       to run SHOW EXPLAIN on anybody.
-  @param  thread_id    Thread whose explain we need
+static 
+const char *target_not_explainable_cmd="Target is not running EXPLAINable command";
 
-  @notes
-  - Attempt to do "SHOW EXPLAIN FOR <myself>" will properly produce "target not
-    running EXPLAINable command".
+/*
+  Store the SHOW EXPLAIN output in the temporary table.
 */
 
-void mysqld_show_explain(THD *thd, const char *calling_user, ulong thread_id)
+int fill_show_explain(THD *thd, TABLE_LIST *table, COND *cond)
 {
+  const char *calling_user;
   THD *tmp;
-  Protocol *protocol= thd->protocol;
-  List<Item> field_list;
-  DBUG_ENTER("mysqld_show_explain");
-  
-  thd->make_explain_field_list(field_list);
-  if (protocol->send_result_set_metadata(&field_list, Protocol::SEND_NUM_ROWS |
-                                                      Protocol::SEND_EOF))
-    DBUG_VOID_RETURN;
+  my_thread_id  thread_id;
+  DBUG_ENTER("fill_show_explain");
 
+  DBUG_ASSERT(cond==NULL);
+  thread_id= thd->lex->show_explain_for_thread->val_int();
+  calling_user= (thd->security_ctx->master_access & PROCESS_ACL) ?  NullS :
+                 thd->security_ctx->priv_user;
   /* 
     Find the thread we need EXPLAIN for. Thread search code was copied from
     kill_one_thread()
@@ -2058,7 +2050,15 @@ void mysqld_show_explain(THD *thd, const char *calling_user, ulong thread_id)
     {
       my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), "PROCESSLIST");
       mysql_mutex_unlock(&tmp->LOCK_thd_data);
-      DBUG_VOID_RETURN;
+      DBUG_RETURN(1);
+    }
+
+    if (tmp == thd)
+    {
+      mysql_mutex_unlock(&tmp->LOCK_thd_data);
+      my_error(ER_ERROR_WHEN_EXECUTING_COMMAND, MYF(0), "SHOW EXPLAIN",
+               target_not_explainable_cmd);
+      DBUG_RETURN(1);
     }
 
     bool bres;
@@ -2071,9 +2071,7 @@ void mysqld_show_explain(THD *thd, const char *calling_user, ulong thread_id)
     Show_explain_request explain_req;
     select_result_explain_buffer *explain_buf;
     
-    explain_buf= new select_result_explain_buffer;
-    explain_buf->thd=thd;
-    explain_buf->protocol= thd->protocol;
+    explain_buf= new select_result_explain_buffer(thd, table->table);
 
     explain_req.explain_buf= explain_buf;
     explain_req.target_thd= tmp;
@@ -2099,29 +2097,22 @@ void mysqld_show_explain(THD *thd, const char *calling_user, ulong thread_id)
       else
       {
         my_error(ER_ERROR_WHEN_EXECUTING_COMMAND, MYF(0), 
-                 "SHOW EXPLAIN",
-                 "Target is not running EXPLAINable command");
+                 "SHOW EXPLAIN", target_not_explainable_cmd);
       }
       bres= TRUE;
-      explain_buf->discard_data();
     }
     else
     {
       push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
                    ER_YES, explain_req.query_str.c_ptr_safe());
     }
-    if (!bres)
-    {
-      explain_buf->flush_data();
-      my_eof(thd);
-    }
+    DBUG_RETURN(bres);
   }
   else
   {
     my_error(ER_NO_SUCH_THREAD, MYF(0), thread_id);
+    DBUG_RETURN(1);
   }
-
-  DBUG_VOID_RETURN;
 }
 
 
@@ -8436,6 +8427,7 @@ ST_FIELD_INFO keycache_fields_info[]=
 };
 
 
+extern ST_FIELD_INFO show_explain_fields_info[];
 /*
   Description of ST_FIELD_INFO in table.h
 
@@ -8467,6 +8459,8 @@ ST_SCHEMA_TABLE schema_tables[]=
   {"EVENTS", events_fields_info, create_schema_table,
    0, make_old_format, 0, -1, -1, 0, 0},
 #endif
+  {"EXPLAIN", show_explain_fields_info, create_schema_table, fill_show_explain,
+  make_old_format, 0, -1, -1, TRUE /*hidden*/ , 0},
   {"FILES", files_fields_info, create_schema_table,
    hton_fill_schema_table, 0, 0, -1, -1, 0, 0},
   {"GLOBAL_STATUS", variables_fields_info, create_schema_table,

sql/sql_yacc.yy

@@ -11617,8 +11617,9 @@ show_param:
         | describe_command FOR_SYM expr
           {
             Lex->sql_command= SQLCOM_SHOW_EXPLAIN;
-            Lex->value_list.empty();
-            Lex->value_list.push_front($3);
+            if (prepare_schema_table(YYTHD, Lex, 0, SCH_EXPLAIN))
+              MYSQL_YYABORT;
+            Lex->show_explain_for_thread= $3;
           }
         ;