Tài liệu MySQL Administrator’s Bible- P16 doc

The MySQL Data Dictionary 21 mysql_version.h is not in the source package, but it is in the mysql-devel package (the compilation process creates mysql_version.h later on). Unfortunately mysql_priv.h is only in the source package, not the mysql-devel package, so you need to download both the source and the mysql-devel packages. On an abstract level, making a custom system view in the INFORMATION_SCHEMA database requires: ■ The field definitions of the system view (that is, the structure of the system view). In our example, we define a system view named MYSQL_HELLO with a field defined as HELLO VARCHAR(64) NOT NULL DEFAULT `’ . ■ The function that populates the system view upon request (that is, the values in the system view). We will define a function to store the string plugin: hello, information_schema!!! into the HELLO field of our MYSQL_HELLO system view. On a more technical level, to create the custom system view, you need to instantiate the ST_SCHEMA_TABLE struct and define two members. One member, field_info, is an array of ST_FIELD_INFO structures, which define the fields in your system view. The values in the ST_FIELD_INFO structure are defined in the source code in the sql/table.h header file and explained in Table 21-3. TABLE 21-3 ST_FIELD_INFO Structure Code Explanation Example Value const char* field_name; Field name ‘‘HELLO’’ uint field_length; In string-type fields, the maximum number of characters. In other fields, the display length. 64 in our example, a string-type field enum enum_field_types field_type; Field data type MYSQL_TYPE_VARCHAR int value; Field value 0 uint field_flags; 0 means NOT NULL and SIGNED.It can be overridden by MY_I_S_MAYBE_NULL, MY_I_S_UNSIGNED, or both constants, separated by | (bitwise or). 0 const char* old_name; Old field name ‘‘Hello’’ uint open_method; How the table is opened. One of SKIP_OPEN_TABLE, OPEN_FRM_ONLY,or OPEN_FULL_TABLE. SKIP_OPEN_TABLE 717 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Part IV Extending Your Skills Our example contains the following code to define the custom system view: 8. static ST_FIELD_INFO mysql_is_hello_field_info[]= 9. { 10. {"HELLO", 64, MYSQL_TYPE_VARCHAR, 0, 0, "Hello", SKIP_OPEN_TABLE}, 11. {NULL, 0, MYSQL_TYPE_NULL, 0, 0, NULL, 0} 12. }; The first structure in the array is the field we are creating. The last structure is an indication that the array is complete, and must be present. We named the array mysql_is_hello_field_ info , which stands for ‘‘the field information of the hello system view in the mysql information schema.’’ Thenextlineofcodeis: 13. int schema_table_store_record(THD *thd, TABLE *table); This line declares the schema_table_store_record function, which we will use later to store a row in a system view. The second member of ST_SCHEMA_TABLE that we need to define is the function that populates the system view, called the fill_table: 14. int mysql_is_hello_fill_table( 15. THD *thd 16. , TABLE_LIST *tables 17. , COND *cond 18. ) 19. { 20. int status; 21. CHARSET_INFO *scs= system_charset_info; 22. TABLE *table= (TABLE *)tables->table; 23. const char *str = "plugin: hello, information_schema!!!"; 24. table->field[0]->store( 25. str 26. , strlen(str) 27. , scs 28. ); 29. status = schema_table_store_record( 30. thd 31. , table 32. ); 33. return status; 34. } In lines 15–17 we see THD *thd again, pointing to the current session, and TABLE_LIST *tables , which is an array of table instantiations of our ‘‘Hello’’ system view. COND *cond is a condition that could be used by our plugin for filtering or optimization, though we will not use it in this example. 718 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The MySQL Data Dictionary 21 The status variable is initialized as an int on line 20. At the end of the function (line 33), status is returned; a value of 1 indicates an error, and a value of 0 indicates success. Then on line 21, CHARSET_INFO *scs is initialized with the character set information. This is needed to properly store the field of our system view. On line 22, TABLE *table is set as the handler to the instantiation of our system view. We ini- tialize the char *str on line 23 with the string we will store in our system view. This means that when we finally install the plugin, we will see str in our system view: mysql> SELECT * FROM INFORMATION_SCHEMA.MYSQL_HELLO; + + | HELLO | + + | plugin: hello, information_schema!!! | + + 1 row in set (0.00 sec) Lines 24–28 store the string str, its length, and the character set scs (defined on line 21) into the first field ( field[0]) of the row. Lines 29–32 store the row into the instantiation of our system view for the current session. If the function that stores the row is successful, status gets a value of 0. If there was an error, status gets a value of 1. status is returned on line 33, thus giving the mysql_is_hello_fill_table function a return value of 0 if it is successful and 1 if there was an error. So far we have defined a system view in an ST_FIELD_INFO array and a fill_table function to populate the system view. We now need to create a plugin function to use these: 35. static int mysql_is_hello_plugin_init(void *p) 36. { 37. ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *)p; 38. schema->fields_info= mysql_is_hello_field_info; 39. schema->fill_table= mysql_is_hello_fill_table; 40. return 0; 41. } The plugin_init function initializes the plugin as an INFORMATION SCHEMA plugin with the fields_info and fill_table we defined previously. Because we have a simple plugin_init function, we have a simple plugin_deinit function as well: 42. static int mysql_is_hello_plugin_deinit(void *p) 43. { 44. return 0; 45. } In our example there is nothing that needs to be done during the plugin_deinit,sowesim- ply return 0, indicating the function was successful. In a more complex example, there may be memory or other resources allocated in the plugin_init function that should be deallocated in the plugin_deinit function. 719 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Part IV Extending Your Skills At this point, we still have not created the plugin. However, we have most of the parts we need to make an INFORMATION_SCHEMA plugin, and can now create the code to define the plugin itself: 46. struct st_mysql_information_schema mysql_is_hello_plugin= 47. { MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION }; 48. mysql_declare_plugin(mysql_is_hello) 49. { 50. MYSQL_INFORMATION_SCHEMA_ PLUGIN, /* type constant */ 51. &mysql_is_hello_plugin, /* type descriptor */ 52. "MYSQL_HELLO", /* Name */ 53. "Roland Bouman (http:// rpbouman.blogspot.com/)", /* Author */ ___________________________________________________________________ 54. "Says hello.", /* Description */ 55. PLUGIN_LICENSE_GPL, /* License */ 56. mysql_is_hello_plugin_init, /* Init function */ 57. mysql_is_hello_plugin_deinit, /* Deinit function */ 58. 0x0010, /* Version (1.0) */ 59. NULL, /* status variables */ 60. NULL, /* system variables */ 61. NULL /* config options */ 62. } 63. mysql_declare_plugin_end; Lines 46–47 define the type descriptor for the plugin, which is set as part of the plugin in line 51. Line 50 defines the type of plugin as an INFORMATION_SCHEMA plugin. Lines 52–55 define metadata that appear after plugin installation in the PLUGINS system view as the PLUGIN_NAME, PLUGIN_AUTHOR, PLUGIN_DESCRIPTION,andPLUGIN_LICENSE fields, respectively. Lines 56–57 point to the previously created plugin_init and plugin_deinit functions, and line 58 defines the version metadata, which corresponds to the value of PLUGIN_VERSION in the PLUGINS system view. Lines 59–61 are pointers to structures containing the status variables, system variables, and configuration options. Our plugin does not have any of these, so we define them as NULL. The entirety of the code is: #include <mysql_priv.h> #include <stdlib.h> #include <ctype.h> 720 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The MySQL Data Dictionary 21 #include <mysql_version.h> #include <mysql/plugin.h> #include <my_global.h> #include <my_dir.h> static ST_FIELD_INFO mysql_is_hello_field_info[]= { {"HELLO", 64, MYSQL_TYPE_VARCHAR, 0, 0, "Hello", SKIP_OPEN_TABLE}, {NULL, 0, MYSQL_TYPE_NULL, 0, 0, NULL, 0} }; int schema_table_store_record(THD *thd, TABLE *table); int mysql_is_hello_fill_table( THD *thd , TABLE_LIST *tables , COND *cond ) { int status; CHARSET_INFO *scs= system_charset_info; TABLE *table= (TABLE *)tables->table; const char *str = "plugin: hello, information_schema!!!"; table->field[0]->store( str , strlen(str) , scs ); status = schema_table_store_record( thd , table ); return status; } static int mysql_is_hello_plugin_init(void *p) { ST_SCHEMA_TABLE *schema= (ST_SCHEMA_TABLE *)p; schema->fields_info= mysql_is_hello_field_info; schema->fill_table= mysql_is_hello_fill_table; return 0; } static int mysql_is_hello_plugin_deinit(void *p) { return 0; } 721 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Part IV Extending Your Skills struct st_mysql_information_schema mysql_is_hello_plugin= { MYSQL_INFORMATION_SCHEMA_INTERFACE_VERSION }; mysql_declare_plugin(mysql_is_hello) { MYSQL_INFORMATION_SCHEMA_ PLUGIN, /* type constant */ &mysql_is_hello_plugin, /* type descriptor */ "MYSQL_HELLO", /* Name */ "Roland Bouman (http:// rpbouman.blogspot.com/)", /* Author */ "Says hello.", /* Description */ PLUGIN_LICENSE_GPL, /* License */ mysql_is_hello_plugin_init, /* Init function */ mysql_is_hello_plugin_deinit, /* Deinit function */ 0x0010, /* Version (1.0) */ NULL, /* status variables */ NULL, /* system variables */ NULL /* config options */ } mysql_declare_plugin_end; Compiling the plugin Now that the code has been created, we need to compile the plugin as a dynamic shared object andthenloaditinto mysqld.Inourexamplewewillsavethesourcecodeinafilenamed mysql_is_hello.cc, and use g++ to compile the source. Table 21-4 shows the compile flags we will use and their meanings. So the complete compile statement is: shell> g++ -DMYSQL_DYNAMIC_PLUGIN –Wall –shared \ -I/path/to/mysql-6.0.x-source/include \ -I/path/to/mysql-6.0.x-source/sql \ -I/usr/include/mysql \ -o mysql_is_hello.so mysql_is_hello.cc The include paths were not specified for stdlib.h and ctype.h, because they are likely in your default include path. On our machines, we found these files in /usr/include, which was in the default include path. If you get errors such as: 722 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The MySQL Data Dictionary 21 error: stdlib.h: No such file or directory error: ctype.h: No such file or directory you should specify the include path for stdlib.h and ctype.h with another -I flag. Some architectures, such as AMD64, require shared libraries to be compiled with the –fPIC flag. If your architecture requires this, you will see output similar to the following when you try to compile: /usr/bin/ld: /tmp/ccNXOEqH.o: relocation R_X86_64_32S against `a local symbol’ can not be used when making a shared object; recompile with –fPIC /tmp/ccNXOEqH.o: could not read symbols: Bad value collect2: ld returned 1 exit status In this case, simply add –fPIC to the list of compile flags and try to compile again. TABLE 21-4 g++ Compile Flags for Compiling a Plugin as a Dynamic Shared Object Compile Flag Meaning -DMYSQL_DYNAMIC_ PLUGIN -D indicates a constant; the constant is MYSQL_DYNAMIC_PLUGIN, which is required to compile the plugin as a dynamic shared object for mysqld. -Wall -W indicates warnings should be shown; all specifies showing all warnings. -shared Compile as a shared, dynamically linked library. -I/path/to/mysql- 6.0.x-source/include The include path for the my_global.h, my_dir.h,and mysql/plugin.h header files. -I/path/to/mysql- 6.0.x-source/sql The include path for the mysql_priv.h header file. -I/usr/include/mysql The include path for the mysql_version.h header file. -o mysql_is_hello.so The output file. The extension .so is traditionally used for shared objects. If all goes well, a dynamic shared plugin will be created with a filename of mysql_is_ hello.so . 723 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Part IV Extending Your Skills Installing the plugin MySQL plugins are installed in mysqld using a MySQL extension to SQL. Thus, mysqld must be running, and no downtime is required to install a plugin. For security purposes, mysqld only looks for plugin libraries in the directory specified by the system variable plugin_dir: mysql> SHOW VARIABLES LIKE ’plugin_dir’; + + + | Variable_name | Value | + + + | plugin_dir | /usr/lib64/mysql/plugin | + + + 1 row in set (0.01 sec) For our example, we make sure the plugin directory exists, copy the plugin to the mysqld plu- gin directory, and ensure that the directory and plugin have appropriate permissions so mysqld can load the plugin: shell> mkdir /usr/lib64/mysql/plugin/ shell> cp mysql_is_hello.so /usr/lib64/mysql/plugin shell> sudo chown –R mysql:mysql /usr/lib64/mysql/plugin/ Now we use the INSTALL PLUGIN statement to install our plugin. The syntax of INSTALL PLUGIN is: INSTALL PLUGIN plugin_name SONAME ’plugin_library’; The plugin_name was set in the plugin metadata (on line 52 of our code). The plugin_library is the name of the compiled plugin file (the complete path to the plugin file is plugin_dir/plugin_library): mysql> INSTALL PLUGIN MYSQL_HELLO SONAME ’mysql_is_hello.so’; Query OK, 0 rows affected (0.00 sec) And our plugin has successfully been installed: mysql> SELECT * FROM INFORMATION_SCHEMA.MYSQL_HELLO; + + | HELLO | + + | plugin: hello, information_schema!!! | + + 1 row in set (0.00 sec) We can now see our plugin in the mysql.plugin system table and the INFORMATION_ SCHEMA.PLUGINS system view: mysql> SELECT * FROM mysql.plugin -> WHERE name=’MYSQL_HELLO’\G 724 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. The MySQL Data Dictionary 21 *************************** 1. row *************************** name: MYSQL_HELLO dl: mysql_is_hello.so 1 row in set (0.00 sec) mysql> SELECT * FROM INFORMATION_SCHEMA.PLUGINS -> WHERE PLUGIN_NAME=’MYSQL_HELLO’\G *************************** 1. row *************************** PLUGIN_NAME: MYSQL_HELLO PLUGIN_VERSION: 0.21 PLUGIN_STATUS: ACTIVE PLUGIN_TYPE: INFORMATION SCHEMA PLUGIN_TYPE_VERSION: 60006.0 PLUGIN_LIBRARY: mysql_is_hello.so PLUGIN_LIBRARY_VERSION: 1.0 PLUGIN_AUTHOR: Roland Bouman (http://rpbouman.blogspot.com/) PLUGIN_DESCRIPTION: Says hello. PLUGIN_LICENSE: GPL 1 row in set (0.00 sec) To uninstall the plugin, run UNINSTALL PLUGIN plugin_name: mysql> UNINSTALL PLUGIN MYSQL_HELLO; Query OK, 0 rows affected (0.00 sec) The plugin is loaded when the INSTALL PLUGIN is run. If you want to change the plugin you have to uninstall the plugin, change the plugin file, and re-install the plugin. If the plugin file changes or is removed while installed on a running server, mysqld will most likely crash. Summary This chapter described the information contained in the MySQL data dictionary, including: ■ All of the metadata in the system views of the INFORMATION_SCHEMA database ■ Many SHOW statements (see Chapter 4 for the remainder of the SHOW statements that show metadata) ■ Many of the system tables in the mysql database ■ Creating custom metadata as INFORMATION_SCHEMA plugins 725 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... whether MySQL Cluster is an appropriate solution for your needs MySQL Cluster is being changed at a very fast rate You can find the most up-to-date information in the Cluster manual at MySQL s website at http:/ /mysql com/cluster The complete documentation is linked from the Cluster Resources page at http:// mysql. com/products/database/cluster/resources.html Currently, the best in-print book about MySQL. .. DRBD to provide read scalability MySQL Proxy MySQL Proxy is a technology that can be used for scaling or high availability It is a proxy server that is transparent; there is not a way for an application or user to tell they are connected to a mysql- proxy process instead of directly to a mysqld process It is written and maintained by MySQL developers, including Jan Kneschke MySQL Proxy is very powerful... database maintenance) MySQL Cluster MySQL Cluster is a great tool for copies of data to be partitioned and kept synchronously on different servers It is a separate version of MySQL MySQL Cluster is freely available, but there is not a version yet for Windows Because it is a very complex and separate product from the standard MySQL server, we will not delve into how to set up a MySQL Cluster We will... cannot use the DRBD device Having a primary and secondary mysqld instance using DRBD is very much like Oracle replication MySQL and DRBD setup These instructions are intended to show how MySQL and DRBD work together They are not step-by-step technical instructions The MySQL manual has good step-by-step instructions at http://dev .mysql. com/ doc/ refman/6.0/en/ha-drbd.html 738 Please purchase PDF Split-Merge... the manual at http://dev .mysql. com /doc/ refman/6.0/en/ mysql- proxy-install-source.html Many operating system distributions, such as Red Hat and Debian, have compiled and packaged mysql- proxy Installing these versions is like installing anything else from your distributions’ package repositories, for example: redhat shell> yum install mysql- proxy debian shell> apt-get install mysql- proxy Proxy backends... use, we will use the binary mysql- proxy, as if we were on a non-Windows system All the examples will work on a Windows system — the only difference is that the binary name is mysql- proxy.exe The minimum configuration mysql- proxy needs is specifying on which port the mysql- proxy daemon will listen, and where mysql- proxy will send requests This is achieved with two options: mysql- proxy proxy-address=host:port... Time: 0 State: NULL Info: show processlist 1 row in set (0.00 sec) mysql> shell> mysql -u root -p -h 127.0.0.1 -P4040 Password: Welcome to the MySQL monitor Commands end with ; or \g Your MySQL connection id is 3 Server version: 6.0.8-alpha-community-log MySQL Community Server (GPL) Type ’help;’ or ’\h’ for help Type ’\c’ to clear the buffer mysql> show processlist\G *************************** 1 row ***************************... on using memcached with MySQL in Chapter 12 There is also information in the MySQL Manual at http://dev .mysql. com /doc/ refman/6.0/en/hamemcached.html and at the memcached website at http://www.danga.com/memcached/ Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark 747 22 Part IV Extending Your Skills Summary This chapter discussed different ways to scale MySQL and make it highly... client traffic to the server and server traffic from the server MySQL Proxy runs on most operating systems: Linux, Windows, Solaris, Mac OS X, and more Using MySQL Proxy, you can: ■ Load balance queries to mysqld: IN THIS APPENDIX Understanding MySQL proxy Learning Lua basics Changing the query backend Changing and injecting queries Understanding MySQL proxy internals ■ In a round-robin fashion ■ By function... traffic to one or more mysqld servers The mysql- proxy daemon can also be scripted, which is where its power and extensibility comes in mysql- proxy accepts scripts written in Lua, a lightweight scripting language used by many applications, including Adobe Photoshop Lightroom, Wireshark, Snort, lighttpd, PlayStation Home, and the popular online game World of Warcraft Installing mysql- proxy MySQL Proxy is not . Skills struct st _mysql_ information_schema mysql_ is_hello_plugin= { MYSQL_ INFORMATION_SCHEMA_INTERFACE_VERSION }; mysql_ declare_plugin (mysql_ is_hello) { MYSQL_ INFORMATION_SCHEMA_ PLUGIN,. plugin itself: 46. struct st _mysql_ information_schema mysql_ is_hello_plugin= 47. { MYSQL_ INFORMATION_SCHEMA_INTERFACE_VERSION }; 48. mysql_ declare_plugin (mysql_ is_hello) 49.