----------------------------------------------------------------------- WORKLOG TASK -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- TASK...........: Add a mysqlbinlog option to change the used database CREATION DATE..: Fri, 07 Aug 2009, 14:57 SUPERVISOR.....: Monty IMPLEMENTOR....: COPIES TO......: CATEGORY.......: Server-RawIdeaBin TASK ID........: 36 (http://askmonty.org/worklog/?tid=36) VERSION........: Server-9.x STATUS.........: Un-Assigned PRIORITY.......: 60 WORKED HOURS...: 0 ESTIMATE.......: 0 (hours remain) ORIG. ESTIMATE.: 0 PROGRESS NOTES: -=-=(Guest - Tue, 15 Sep 2009, 12:12)=-=- Low Level Design modified. --- /tmp/wklog.36.old.3961 2009-09-15 12:12:26.000000000 +0300 +++ /tmp/wklog.36.new.3961 2009-09-15 12:12:26.000000000 +0300 @@ -144,6 +144,8 @@ 3. Supporting rewrite-db for SBR events --------------------------------------- +Limited to emiting USE <db_to> instead of USE <db_from>. + USE statements can be emited by mysqlbinlog as a result of processing the following events (see process_event() function): -=-=(Guest - Tue, 15 Sep 2009, 12:08)=-=- Low Level Design modified. --- /tmp/wklog.36.old.3794 2009-09-15 12:08:54.000000000 +0300 +++ /tmp/wklog.36.new.3794 2009-09-15 12:08:54.000000000 +0300 @@ -1 +1,229 @@ +Content +------- +1. Adding rewrite-db option +2. Supporting rewrite-db option for RBR events +3. Supporting rewrite-db option for SBR events + (Limited to affecting only USE statements) +4. Current status + +1. Adding rewrite-db option +--------------------------- + +1.1. Syntax: + --rewrite-db='db_from->db_to' + +1.2. Add 'OPT_REWRITE_DB' to 'options_client' (in client_priv.h). + +1.3. In mysqlbinlog.cc: + +- Add { "rewrite-db", OPT_REWRITE_DB, ...} record to my_long_options: +- Add Rpl_filter object to mysqlbinlog.cc + + Rpl_filter* binlog_filter; + +- Add corresponding switch case to get_one_option(): + + case OPT_REWRITE_DB: + <extract db-from and db-to strings> + binlog_filter->add_db_rewrite(db_from, db_to); + break; + . +Note. To make Rpl_filter usable in a MYSQL_CLIENT context, few small +additional changes are required: + +- In sql_list.cc/h, Sql_alloc::new(size_t) and Sql_alloc::new[](size_t) + uses sql_alloc() which is THD dependent. These are to be modified + as follows: + + #ifdef MYSQL_CLIENT + extern MEM_ROOT sql_list_client_mem_root; // defined in sql_list.cc + #endif + + class Sql_alloc + { ... + static void *operator new(size_t size) throw () + { + #ifndef MYSQL_CLIENT + return sql_alloc(size); + #else + return alloc_root(&sql_list_client_mem_root, size); + #endif + } + static void *operator new[](size_t size) throw () + { + #ifndef MYSQL_CLIENT + return sql_alloc(size); + #else + return alloc_root(&sql_list_client_mem_root, size); + #endif + } + ... + } + +- In rpl_filter.cc: + + Rpl_filter::Rpl_filter() : + ... + { + #ifdef MYSQL_CLIENT + init_alloc_root(&sql_list_client_mem_root, ...); + #endif + ... + } + + Rpl_filter::~Rpl_filter() + { ... + #ifdef MYSQL_CLIENT + free_root(&sql_list_client_mem_root, ...); + #endif + } + +2. Supporting rewrite-db for RBR events +--------------------------------------- + +In binlog, each row operation event is preceded by Table map event(s) which maps +table id(s) to database and table names. So, it's enough to support rewriting +database name in a Table map. + +2.1. Add rewrite_db() member to Table_map_log_event: + + int Table_map_log_event::rewrite_db( + const char* new_db, + size_t new_db_len, + const Format_description_log_event* desc) + { + /* 1. In temp_buf member (possibly reallocating it) rewrite + event length, db length, and db parts + 2. Change m_dblen and m_dbnam members + */ + } + +Comment. This function assumes that temp_buf member contains Table map +binlog representaion (temp_buf is used for creating corresponding +BINLOG statement). + +2.2. In mysqlbinlog modify corresponding switch case in the +process_event() function: + + Exit_status process_event( + PRINT_EVENT_INFO *print_event_info, + Log_event *ev, ...) + { + ... + switch (ev_type) { + ... + case TABLE_MAP_EVENT: + { + Table_map_log_event *map= ((Table_map_log_event *)ev); + if (shall_skip_database(map->get_db_name())) + { ... + } + // WL36 + size_t new_len= 0; + const char* new_db= binlog_filter->get_rewrite_db( + map->get_db_name(), &new_len); + if (new_len && map->rewrite_db(new_db, new_len, + glob_description_event)) + { error("Could not rewrite database name"); + goto err; + } + } + case WRITE_ROWS_EVENT: + case DELETE_ROWS_EVENT: + case UPDATE_ROWS_EVENT: + ... + } + ... + } + +Comment. Rpl_filter::get_rewrite_db(db_from, &len): if filter contains +a (db_from, db_to) pair, this function returns pointer to db_to and +sets len = db_to length; otherwise, it returns db_from and does not +change len value. + +3. Supporting rewrite-db for SBR events +--------------------------------------- + +USE statements can be emited by mysqlbinlog as a result of processing the +following events (see process_event() function): + +- Query_log_event +- Execute_load_query_log_event +- Create_file_log_event + +TODO. Needed to check this list requires carefully !!! + +Conditions for emiting use-statement: +- LOG_EVENT_SUPPRESS_USE_F is OFF for the event + (e.g. it is ON for 'create database' statement) +- event's db name differs from db_name in PRINT_EVENT_INFO + (PRINT_EVENT_INFO keeps db name of the last issued USE statement; + initially, this db name is empty). + +3.1. In mysqlbinlog.cc + +- Add the following function: + + void print_use_stmt(Log_event* event, PRINT_EVENT_INFO* pinfo) + { + if (event->flags & LOG_EVENT_SUPPRESS_USE_F) + return; + /* + - For events listed above get db_from = event->db; + - If db_from is the same as pinfo->db then return; + - If there is rewrite-db rule db_from->db_to, + set db = db_to. Else set db = db_from; + - Print "use <db>" to mysqlbinlog output + - Set pinfo->db = db_from + (this suppresses emiting use-statements by corresponding + log_event's print-function) + */ + } + +- In process_event() function add print_use_stmt() invocations where + needed (according to the events lis above), e.g.: + + Exit_status process_event( + PRINT_EVENT_INFO *print_event_info, + Log_event *ev, ...) + { + ... + switch (ev_type) { + case QUERY_EVENT: + if (shall_skip_database(((Query_log_event*)ev)->db)) + goto end; + if (opt_base64_output_mode == BASE64_OUTPUT_ALWAYS) + { + // Possibly in case of rewite-db rule for ev->db + // a warning should be emited here (see note below) + ... write_event_header_and_base64(ev, ...) ... + } + else + { + print_use_stmt((Query_log_event*)ev, print_event_info); + ev->print(result_file, print_event_info); + } + break; + ... + } + ... + } + +Note. write_event_header_and_base64() does not print use-statement. It +produces BINLOG statement using ev->temp_buf content (i.e. the binary +log representation of the event). We don't rewrite temp_buf here with +db_to name (as we do it for Table map event) - this implies the +limitation 3 mentioned above. +Question: Is supporting of rewite_db + --base64-output really needed +currently? + +4. Current status +----------------- + +The outlined design (implemented for mysql-5.1.37) is tested for +simple test-cases. + +TODO. 1. Check list of events which can emit use-statement. + 2. Supporting of rewite_db + --base64-output ? + -=-=(Guest - Mon, 14 Sep 2009, 11:51)=-=- Low Level Design modified. --- /tmp/wklog.36.old.9711 2009-09-14 11:51:43.000000000 +0300 +++ /tmp/wklog.36.new.9711 2009-09-14 11:51:43.000000000 +0300 @@ -1 +1 @@ -Pay no attention: just check for having access + -=-=(Guest - Mon, 14 Sep 2009, 11:51)=-=- Low Level Design modified. --- /tmp/wklog.36.old.9678 2009-09-14 11:51:28.000000000 +0300 +++ /tmp/wklog.36.new.9678 2009-09-14 11:51:28.000000000 +0300 @@ -1 +1 @@ - +Pay no attention: just check for having access -=-=(Knielsen - Mon, 17 Aug 2009, 12:44)=-=- High-Level Specification modified. --- /tmp/wklog.36.old.7834 2009-08-17 12:44:17.000000000 +0300 +++ /tmp/wklog.36.new.7834 2009-08-17 12:44:17.000000000 +0300 @@ -13,7 +13,9 @@ statement refers to tables in current database, so that changing the current database will make the statement to work on a table in a different database). -See also MySQL BUG#42941. +See also MySQL BUG#42941. Note this bug is fixed in MySQL 5.1.37, which is not +merged into MariaDB at the time of writing, but planned to be merged before +release. What we could do ---------------- -=-=(Guest - Sun, 16 Aug 2009, 17:11)=-=- High-Level Specification modified. --- /tmp/wklog.36.old.27162 2009-08-16 17:11:12.000000000 +0300 +++ /tmp/wklog.36.new.27162 2009-08-16 17:11:12.000000000 +0300 @@ -13,6 +13,8 @@ statement refers to tables in current database, so that changing the current database will make the statement to work on a table in a different database). +See also MySQL BUG#42941. + What we could do ---------------- -=-=(Psergey - Mon, 10 Aug 2009, 15:41)=-=- High-Level Specification modified. --- /tmp/wklog.36.old.13035 2009-08-10 15:41:51.000000000 +0300 +++ /tmp/wklog.36.new.13035 2009-08-10 15:41:51.000000000 +0300 @@ -1,5 +1,7 @@ Context ------- +(See http://askmonty.org/wiki/index.php/Scratch/ReplicationOptions for global +overview) At the moment, the server has a replication slave option --replicate-rewrite-db="from->to" -=-=(Guest - Mon, 10 Aug 2009, 11:12)=-=- High-Level Specification modified. --- /tmp/wklog.36.old.6580 2009-08-10 11:12:36.000000000 +0300 +++ /tmp/wklog.36.new.6580 2009-08-10 11:12:36.000000000 +0300 @@ -1,4 +1,3 @@ - Context ------- At the moment, the server has a replication slave option @@ -67,6 +66,6 @@ It will be possible to do the rewrites either on the slave ( --replicate-rewrite-db will work for all kinds of statements), or in -mysqlbinlog (adding a comment is easy and doesn't require use to parse the -statement). +mysqlbinlog (adding a comment is easy and doesn't require mysqlbinlog to +parse the statement). -=-=(Psergey - Sun, 09 Aug 2009, 23:53)=-=- High-Level Specification modified. --- /tmp/wklog.36.old.13425 2009-08-09 23:53:54.000000000 +0300 +++ /tmp/wklog.36.new.13425 2009-08-09 23:53:54.000000000 +0300 @@ -1 +1,72 @@ +Context +------- +At the moment, the server has a replication slave option + + --replicate-rewrite-db="from->to" + +the option affects +- Table_map_log_event (all RBR events) +- Load_log_event (LOAD DATA) +- Query_log_event (SBR-based updates, with the usual assumption that the + statement refers to tables in current database, so that changing the current + database will make the statement to work on a table in a different database). + +What we could do +---------------- + +Option1: make mysqlbinlog accept --replicate-rewrite-db option +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Make mysqlbinlog accept --replicate-rewrite-db options and process them to the +same extent as replication slave would process --replicate-rewrite-db option. + + +Option2: Add database-agnostic RBR events and --strip-db option +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Right now RBR events require a databasename. It is not possible to have RBR +event stream that won't mention which database the events are for. When I +tried to use debugger and specify empty database name, attempt to apply the +binlog resulted in this error: + +090809 17:38:44 [ERROR] Slave SQL: Error 'Table '.tablename' doesn't exist' on +opening tables, + +We could do as follows: +- Make the server interpret empty database name in RBR event (i.e. in a + Table_map_log_event) as "use current database". Binlog slave thread + probably should not allow such events as it doesn't have a natural current + database. +- Add a mysqlbinlog --strip-db option that would + = not produce any "USE dbname" statements + = change databasename for all RBR events to be empty + +That way, mysqlbinlog output will be database-agnostic and apply to the +current database. +(this will have the usual limitations that we assume that all statements in +the binlog refer to the current database). + +Option3: Enhance database rewrite +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If there is a need to support database change for statements that use +dbname.tablename notation and are replicated as statements (i.e. are DDL +statements and/or DML statements that are binlogged as statements), +then that could be supported as follows: + +- Make the server's parser recognize special form of comments + + /* !database-alias(oldname,newname) */ + + and save the mapping somewhere + +- Put the hooks in table open and name resolution code to use the saved + mapping. + + +Once we've done the above, it will be easy to perform a complete, +no-compromise or restrictions database name change in binary log. + +It will be possible to do the rewrites either on the slave ( +--replicate-rewrite-db will work for all kinds of statements), or in +mysqlbinlog (adding a comment is easy and doesn't require use to parse the +statement). + -=-=(Psergey - Sun, 09 Aug 2009, 12:27)=-=- Dependency created: 39 now depends on 36 ------------------------------------------------------------ -=-=(View All Progress Notes, 11 total)=-=- http://askmonty.org/worklog/index.pl?tid=36&nolimit=1 DESCRIPTION: Sometimes there is a need to take a binary log and apply it to a database with a different name than the original name of the database on binlog producer. If one is using statement-based replication, he can achieve this by grepping out "USE dbname" statements out of the output of mysqlbinlog(*). With row-based replication this is no longer possible, as database name is encoded within the the BINLOG '....' statement. This task is about adding an option to mysqlbinlog that would allow to change the names of used databases in both RBR and SBR events. (*) this implies that all statements refer to tables in the current database, doesn't catch updates made inside stored functions and so forth, but still works for a practially-important subset of cases. HIGH-LEVEL SPECIFICATION: Context ------- (See http://askmonty.org/wiki/index.php/Scratch/ReplicationOptions for global overview) At the moment, the server has a replication slave option --replicate-rewrite-db="from->to" the option affects - Table_map_log_event (all RBR events) - Load_log_event (LOAD DATA) - Query_log_event (SBR-based updates, with the usual assumption that the statement refers to tables in current database, so that changing the current database will make the statement to work on a table in a different database). See also MySQL BUG#42941. Note this bug is fixed in MySQL 5.1.37, which is not merged into MariaDB at the time of writing, but planned to be merged before release. What we could do ---------------- Option1: make mysqlbinlog accept --replicate-rewrite-db option ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Make mysqlbinlog accept --replicate-rewrite-db options and process them to the same extent as replication slave would process --replicate-rewrite-db option. Option2: Add database-agnostic RBR events and --strip-db option ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Right now RBR events require a databasename. It is not possible to have RBR event stream that won't mention which database the events are for. When I tried to use debugger and specify empty database name, attempt to apply the binlog resulted in this error: 090809 17:38:44 [ERROR] Slave SQL: Error 'Table '.tablename' doesn't exist' on opening tables, We could do as follows: - Make the server interpret empty database name in RBR event (i.e. in a Table_map_log_event) as "use current database". Binlog slave thread probably should not allow such events as it doesn't have a natural current database. - Add a mysqlbinlog --strip-db option that would = not produce any "USE dbname" statements = change databasename for all RBR events to be empty That way, mysqlbinlog output will be database-agnostic and apply to the current database. (this will have the usual limitations that we assume that all statements in the binlog refer to the current database). Option3: Enhance database rewrite ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If there is a need to support database change for statements that use dbname.tablename notation and are replicated as statements (i.e. are DDL statements and/or DML statements that are binlogged as statements), then that could be supported as follows: - Make the server's parser recognize special form of comments /* !database-alias(oldname,newname) */ and save the mapping somewhere - Put the hooks in table open and name resolution code to use the saved mapping. Once we've done the above, it will be easy to perform a complete, no-compromise or restrictions database name change in binary log. It will be possible to do the rewrites either on the slave ( --replicate-rewrite-db will work for all kinds of statements), or in mysqlbinlog (adding a comment is easy and doesn't require mysqlbinlog to parse the statement). LOW-LEVEL DESIGN: Content ------- 1. Adding rewrite-db option 2. Supporting rewrite-db option for RBR events 3. Supporting rewrite-db option for SBR events (Limited to affecting only USE statements) 4. Current status 1. Adding rewrite-db option --------------------------- 1.1. Syntax: --rewrite-db='db_from->db_to' 1.2. Add 'OPT_REWRITE_DB' to 'options_client' (in client_priv.h). 1.3. In mysqlbinlog.cc: - Add { "rewrite-db", OPT_REWRITE_DB, ...} record to my_long_options: - Add Rpl_filter object to mysqlbinlog.cc Rpl_filter* binlog_filter; - Add corresponding switch case to get_one_option(): case OPT_REWRITE_DB: <extract db-from and db-to strings> binlog_filter->add_db_rewrite(db_from, db_to); break; . Note. To make Rpl_filter usable in a MYSQL_CLIENT context, few small additional changes are required: - In sql_list.cc/h, Sql_alloc::new(size_t) and Sql_alloc::new[](size_t) uses sql_alloc() which is THD dependent. These are to be modified as follows: #ifdef MYSQL_CLIENT extern MEM_ROOT sql_list_client_mem_root; // defined in sql_list.cc #endif class Sql_alloc { ... static void *operator new(size_t size) throw () { #ifndef MYSQL_CLIENT return sql_alloc(size); #else return alloc_root(&sql_list_client_mem_root, size); #endif } static void *operator new[](size_t size) throw () { #ifndef MYSQL_CLIENT return sql_alloc(size); #else return alloc_root(&sql_list_client_mem_root, size); #endif } ... } - In rpl_filter.cc: Rpl_filter::Rpl_filter() : ... { #ifdef MYSQL_CLIENT init_alloc_root(&sql_list_client_mem_root, ...); #endif ... } Rpl_filter::~Rpl_filter() { ... #ifdef MYSQL_CLIENT free_root(&sql_list_client_mem_root, ...); #endif } 2. Supporting rewrite-db for RBR events --------------------------------------- In binlog, each row operation event is preceded by Table map event(s) which maps table id(s) to database and table names. So, it's enough to support rewriting database name in a Table map. 2.1. Add rewrite_db() member to Table_map_log_event: int Table_map_log_event::rewrite_db( const char* new_db, size_t new_db_len, const Format_description_log_event* desc) { /* 1. In temp_buf member (possibly reallocating it) rewrite event length, db length, and db parts 2. Change m_dblen and m_dbnam members */ } Comment. This function assumes that temp_buf member contains Table map binlog representaion (temp_buf is used for creating corresponding BINLOG statement). 2.2. In mysqlbinlog modify corresponding switch case in the process_event() function: Exit_status process_event( PRINT_EVENT_INFO *print_event_info, Log_event *ev, ...) { ... switch (ev_type) { ... case TABLE_MAP_EVENT: { Table_map_log_event *map= ((Table_map_log_event *)ev); if (shall_skip_database(map->get_db_name())) { ... } // WL36 size_t new_len= 0; const char* new_db= binlog_filter->get_rewrite_db( map->get_db_name(), &new_len); if (new_len && map->rewrite_db(new_db, new_len, glob_description_event)) { error("Could not rewrite database name"); goto err; } } case WRITE_ROWS_EVENT: case DELETE_ROWS_EVENT: case UPDATE_ROWS_EVENT: ... } ... } Comment. Rpl_filter::get_rewrite_db(db_from, &len): if filter contains a (db_from, db_to) pair, this function returns pointer to db_to and sets len = db_to length; otherwise, it returns db_from and does not change len value. 3. Supporting rewrite-db for SBR events --------------------------------------- Limited to emiting USE <db_to> instead of USE <db_from>. USE statements can be emited by mysqlbinlog as a result of processing the following events (see process_event() function): - Query_log_event - Execute_load_query_log_event - Create_file_log_event TODO. Needed to check this list requires carefully !!! Conditions for emiting use-statement: - LOG_EVENT_SUPPRESS_USE_F is OFF for the event (e.g. it is ON for 'create database' statement) - event's db name differs from db_name in PRINT_EVENT_INFO (PRINT_EVENT_INFO keeps db name of the last issued USE statement; initially, this db name is empty). 3.1. In mysqlbinlog.cc - Add the following function: void print_use_stmt(Log_event* event, PRINT_EVENT_INFO* pinfo) { if (event->flags & LOG_EVENT_SUPPRESS_USE_F) return; /* - For events listed above get db_from = event->db; - If db_from is the same as pinfo->db then return; - If there is rewrite-db rule db_from->db_to, set db = db_to. Else set db = db_from; - Print "use <db>" to mysqlbinlog output - Set pinfo->db = db_from (this suppresses emiting use-statements by corresponding log_event's print-function) */ } - In process_event() function add print_use_stmt() invocations where needed (according to the events lis above), e.g.: Exit_status process_event( PRINT_EVENT_INFO *print_event_info, Log_event *ev, ...) { ... switch (ev_type) { case QUERY_EVENT: if (shall_skip_database(((Query_log_event*)ev)->db)) goto end; if (opt_base64_output_mode == BASE64_OUTPUT_ALWAYS) { // Possibly in case of rewite-db rule for ev->db // a warning should be emited here (see note below) ... write_event_header_and_base64(ev, ...) ... } else { print_use_stmt((Query_log_event*)ev, print_event_info); ev->print(result_file, print_event_info); } break; ... } ... } Note. write_event_header_and_base64() does not print use-statement. It produces BINLOG statement using ev->temp_buf content (i.e. the binary log representation of the event). We don't rewrite temp_buf here with db_to name (as we do it for Table map event) - this implies the limitation 3 mentioned above. Question: Is supporting of rewite_db + --base64-output really needed currently? 4. Current status ----------------- The outlined design (implemented for mysql-5.1.37) is tested for simple test-cases. TODO. 1. Check list of events which can emit use-statement. 2. Supporting of rewite_db + --base64-output ? ESTIMATED WORK TIME ESTIMATED COMPLETION DATE ----------------------------------------------------------------------- WorkLog (v3.5.9)