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Message #03694
MWL#132: TC plugin, patch for (possible) code review
Hi Serg,
And here is the patch for MWL#132, TC plugin.
The patch is fairly short, as most of the real code changes are included in
MWL#116. This patch is mainly about introducing a new plugin interface for
transaction coordinators, and making the three existing TCs in log.cc into
built-in plugins.
My main motivation for this work was Galera, but when I discussed with them at
the Istanbul meeting, I learned that they are not so interested in internal
2-phase commit (instead they download a complete database snapshot at node
recovery after a node crash).
So now I do not have an example of an external TC plugin implementation. My
idea is to implement the MWL#120: stacked event generators. I could then use
this to implement a simple TC example that does (very) basic synchroneous
replication (eg. maybe insert-only with little error handling or
something). This could be a nice example of how to use the facilities that TC
plugins provide for controlling the commit process etc.
So I would like your opinion as to whether this should be pushed to 5.3 now or
wait for MWL#120 (assuming you think it can be made suitable for pushing at
all, of course :-).
- Kristian.
=== modified file 'include/mysql/plugin.h'
--- include/mysql/plugin.h 2010-05-26 18:55:40 +0000
+++ include/mysql/plugin.h 2010-10-04 10:48:08 +0000
@@ -75,7 +75,8 @@ typedef struct st_mysql_xid MYSQL_XID;
#define MYSQL_FTPARSER_PLUGIN 2 /* Full-text parser plugin */
#define MYSQL_DAEMON_PLUGIN 3 /* The daemon/raw plugin type */
#define MYSQL_INFORMATION_SCHEMA_PLUGIN 4 /* The I_S plugin type */
-#define MYSQL_MAX_PLUGIN_TYPE_NUM 5 /* The number of plugin types */
+#define MYSQL_TC_PLUGIN 5 /* Transaction coordinator */
+#define MYSQL_MAX_PLUGIN_TYPE_NUM 6 /* The number of plugin types */
/* We use the following strings to define licenses for plugins */
#define PLUGIN_LICENSE_PROPRIETARY 0
@@ -600,10 +601,10 @@ struct st_mysql_ftparser
};
/*************************************************************************
- API for Storage Engine plugin. (MYSQL_DAEMON_PLUGIN)
+ API for Daemon/raw plugin. (MYSQL_DAEMON_PLUGIN)
*/
-/* handlertons of different MySQL releases are incompatible */
+/* Internals of different MySQL releases are incompatible */
#define MYSQL_DAEMON_INTERFACE_VERSION (MYSQL_VERSION_ID << 8)
/*************************************************************************
@@ -653,6 +654,41 @@ struct st_mysql_information_schema
int interface_version;
};
+/*************************************************************************
+ API for Transaction Coordinator plugin. (MYSQL_TC_PLUGIN)
+*/
+
+/* TCs of different MySQL releases are incompatible */
+#define MYSQL_TC_VERSION (MYSQL_VERSION_ID << 8)
+
+/*
+ The real API is in sql/log.h
+ Here we define only the descriptor structure, that is referred from
+ st_mysql_plugin.
+*/
+
+struct st_mysql_tc
+{
+ int interface_version;
+ /*
+ This method is called to register a plugin as the transaction coordinator.
+ The method returns the TC_LOG * for the class object.
+
+ A plugin can also return NULL to abstain from being a transaction
+ coordinator.
+
+ The plugin can be asked twice to register. First time yield is passed as
+ 1; the intension is that in this phase only the plugin explicitly
+ requested by the user should ask to be the primary (and it is a fatal
+ error if two plugins compete to be TC in this phase).
+
+ Second time yield is passed as 0; in this case it means there was no
+ explicit request for a particular TC, and whoever returns non-NULL in this
+ phase first becomes the TC.
+ */
+ struct TC_LOG *(*register_as_primary_tc)(void *arg, int yield);
+};
+
/*
st_mysql_value struct for reading values from mysqld.
=== modified file 'include/mysql/plugin.h.pp'
--- include/mysql/plugin.h.pp 2010-05-26 18:55:40 +0000
+++ include/mysql/plugin.h.pp 2010-10-04 10:48:08 +0000
@@ -106,6 +106,11 @@ struct st_mysql_information_schema
{
int interface_version;
};
+struct st_mysql_tc
+{
+ int interface_version;
+ struct TC_LOG *(*register_as_primary_tc)(void *arg, int yield);
+};
struct st_mysql_value
{
int (*value_type)(struct st_mysql_value *);
=== modified file 'sql/log.cc'
--- sql/log.cc 2010-10-01 08:49:57 +0000
+++ sql/log.cc 2010-10-05 07:24:25 +0000
@@ -166,6 +166,8 @@ public:
~binlog_trx_data()
{
DBUG_ASSERT(pending() == NULL);
+ pthread_cond_destroy(&COND_group_commit);
+ pthread_mutex_destroy(&LOCK_group_commit);
close_cached_file(&trans_log);
}
@@ -6531,6 +6533,49 @@ err1:
"--tc-heuristic-recover={commit|rollback}");
return 1;
}
+
+static TC_LOG *
+tc_log_mmap_register(void *arg __attribute__((unused)), int yield)
+{
+ /*
+ In the first round, we let any other plugin that wants to be the TC
+ get preference (eg. the binary log).
+
+ But if no-one else wants the TC role, TC_LOG_MMAP serves as a fallback
+ that only does crash recovery (of multi-engine transactions).
+
+ If we do not have multiple engines that are capable of transactions,
+ we do not even need recovery, and TC_LOG_DUMMY will be selected instead.
+ */
+ if (yield || total_ha_2pc <= 1)
+ return NULL;
+
+ return &tc_log_mmap;
+}
+
+static struct st_mysql_tc tc_log_mmap_plugin=
+{
+ MYSQL_TC_VERSION,
+ tc_log_mmap_register
+};
+
+mysql_declare_plugin(tc_log_mmap)
+{
+ MYSQL_TC_PLUGIN,
+ &tc_log_mmap_plugin,
+ "tc_log_mmap",
+ "MariaDB",
+ "Default non-binlog TC, uses mmap()'ed scoreboard for 2pc recovery",
+ PLUGIN_LICENSE_GPL,
+ NULL,
+ NULL,
+ 0x0100 /* 1.0 */,
+ NULL,
+ NULL,
+ NULL
+}
+mysql_declare_plugin_end;
+
#endif
TC_LOG *tc_log;
@@ -6815,6 +6860,79 @@ ulonglong mysql_bin_log_file_pos(void)
}
#endif /* INNODB_COMPATIBILITY_HOOKS */
+struct select_tc_plugin_data
+{
+ TC_LOG *selected;
+ const char *selected_name;
+ int yield;
+};
+
+static my_bool
+select_tc_plugin_cb(THD *thd __attribute__((unused)), plugin_ref plugin,
+ void *arg)
+{
+ select_tc_plugin_data *data= static_cast<select_tc_plugin_data *>(arg);
+ /* In the second phase, skip everything after the first TC that registers. */
+ if (!data->yield && data->selected)
+ return FALSE;
+ st_mysql_tc *tcton= static_cast<st_mysql_tc *>(plugin_decl(plugin)->info);
+ TC_LOG *candidate=
+ (*tcton->register_as_primary_tc)(plugin_int_to_ref(plugin), data->yield);
+ if (candidate)
+ {
+ const char *candidate_name= plugin_name(plugin)->str;
+ if (data->selected)
+ {
+ sql_print_error("Fatal: plugins %s and %s both registered as "
+ "transaction\ncoordinator, but only one is allowed.\n"
+ "Please disable one of them.", data->selected_name,
+ candidate_name);
+ return TRUE;
+ }
+ data->selected= candidate;
+ data->selected_name= candidate_name;
+ }
+ return FALSE;
+}
+
+/*
+ Select which plugin to use for the transaction coordinator
+ (there can be only one).
+
+ First, ask all plugins if they insist to be the prefered TC. If more than
+ one does, it is an error.
+
+ If no one insists, try again, this time picking the first one that is
+ willing to act as TC (there will always be one, as either tc_log_dummy or
+ tc_log_mmap will step up).
+*/
+TC_LOG *
+select_tc_plugin()
+{
+ my_bool error;
+ select_tc_plugin_data data;
+ DBUG_ENTER("select_tc_plugin");
+
+ data.selected= NULL;
+ data.yield= 1;
+ for (;;)
+ {
+ error= plugin_foreach(NULL, select_tc_plugin_cb, MYSQL_TC_PLUGIN, &data);
+ if (error)
+ DBUG_RETURN(NULL);
+ if (data.selected)
+ DBUG_RETURN(data.selected);
+ if (!data.yield)
+ break;
+ else
+ data.yield= 0;
+ }
+
+ sql_print_error("Fatal: No transaction coordinator plugin available");
+
+ DBUG_RETURN(NULL);
+}
+
static ulonglong binlog_status_var_num_commits;
static ulonglong binlog_status_var_num_group_commits;
@@ -6885,6 +7003,24 @@ TC_LOG_BINLOG::set_status_variables()
struct st_mysql_storage_engine binlog_storage_engine=
{ MYSQL_HANDLERTON_INTERFACE_VERSION };
+static TC_LOG *
+tc_log_binlog_register(void *arg __attribute__((unused)),
+ int yield __attribute__((unused)))
+{
+ DBUG_ENTER("tc_log_binlog_create");
+
+ if (opt_bin_log && total_ha_2pc > 1)
+ DBUG_RETURN(&mysql_bin_log);
+
+ DBUG_RETURN(NULL);
+}
+
+static struct st_mysql_tc tc_log_binlog_plugin=
+{
+ MYSQL_TC_VERSION,
+ tc_log_binlog_register
+};
+
mysql_declare_plugin(binlog)
{
MYSQL_STORAGE_ENGINE_PLUGIN,
@@ -6903,5 +7039,57 @@ mysql_declare_plugin(binlog)
NULL, /* system variables */
#endif
NULL /* config options */
+},
+{
+ MYSQL_TC_PLUGIN,
+ &tc_log_binlog_plugin,
+ "tc_log_binlog",
+ "MariaDB",
+ "TC for the binary log",
+ PLUGIN_LICENSE_GPL,
+ NULL,
+ NULL,
+ 0x0100 /* 1.0 */,
+ NULL,
+ NULL,
+ NULL
+}
+mysql_declare_plugin_end;
+
+
+/*
+ Dummy TC plugin with empty implementation.
+ This is used when there is at most one XA-capable engine, in which case
+ the transaction coordinator is not used.
+*/
+
+static TC_LOG *
+tc_log_dummy_register(void *arg __attribute__((unused)), int yield)
+{
+ if (yield || total_ha_2pc > 1)
+ return NULL;
+ return &tc_log_dummy;
+}
+
+static struct st_mysql_tc tc_log_dummy_plugin=
+{
+ MYSQL_TC_VERSION,
+ tc_log_dummy_register
+};
+
+mysql_declare_plugin(tc_log_dummy)
+{
+ MYSQL_TC_PLUGIN,
+ &tc_log_dummy_plugin,
+ "tc_log_dummy",
+ "MariaDB",
+ "Dummy TC plugin for server without 2-phase commit",
+ PLUGIN_LICENSE_GPL,
+ NULL,
+ NULL,
+ 0x0100 /* 1.0 */,
+ NULL,
+ NULL,
+ NULL
}
mysql_declare_plugin_end;
=== modified file 'sql/log.h'
--- sql/log.h 2010-10-01 08:49:57 +0000
+++ sql/log.h 2010-10-04 10:48:08 +0000
@@ -781,4 +781,6 @@ extern TYPELIB binlog_format_typelib;
int query_error_code(THD *thd, bool not_killed);
+TC_LOG *select_tc_plugin();
+
#endif /* LOG_H */
=== modified file 'sql/mysqld.cc'
--- sql/mysqld.cc 2010-10-01 08:49:57 +0000
+++ sql/mysqld.cc 2010-10-04 10:48:08 +0000
@@ -4283,10 +4283,11 @@ a file name for --log-bin-index option",
}
#endif
- tc_log= (total_ha_2pc > 1 ? (opt_bin_log ?
- (TC_LOG *) &mysql_bin_log :
- (TC_LOG *) &tc_log_mmap) :
- (TC_LOG *) &tc_log_dummy);
+ tc_log= select_tc_plugin();
+ if (!tc_log)
+ {
+ unireg_abort(1);
+ }
if (tc_log->open(opt_bin_log ? opt_bin_logname : opt_tc_log_file))
{
=== modified file 'sql/sql_builtin.cc.in'
--- sql/sql_builtin.cc.in 2009-11-29 23:08:56 +0000
+++ sql/sql_builtin.cc.in 2010-10-04 10:48:08 +0000
@@ -19,10 +19,10 @@
typedef struct st_mysql_plugin builtin_plugin[];
extern builtin_plugin
- builtin_binlog_plugin@mysql_plugin_defs@;
+ builtin_tc_log_dummy_plugin, builtin_tc_log_mmap_plugin, builtin_binlog_plugin@mysql_plugin_defs@;
struct st_mysql_plugin *mysqld_builtins[]=
{
- builtin_binlog_plugin@mysql_plugin_defs@,(struct st_mysql_plugin *)0
+ builtin_tc_log_dummy_plugin, builtin_tc_log_mmap_plugin, builtin_binlog_plugin@mysql_plugin_defs@,(struct st_mysql_plugin *)0
};
=== modified file 'sql/sql_plugin.cc'
--- sql/sql_plugin.cc 2010-09-21 14:21:30 +0000
+++ sql/sql_plugin.cc 2010-10-04 10:48:08 +0000
@@ -59,12 +59,12 @@ extern int finalize_schema_table(st_plug
*/
plugin_type_init plugin_type_initialize[MYSQL_MAX_PLUGIN_TYPE_NUM]=
{
- 0,ha_initialize_handlerton,0,0,initialize_schema_table
+ 0,ha_initialize_handlerton,0,0,initialize_schema_table,0
};
plugin_type_init plugin_type_deinitialize[MYSQL_MAX_PLUGIN_TYPE_NUM]=
{
- 0,ha_finalize_handlerton,0,0,finalize_schema_table
+ 0,ha_finalize_handlerton,0,0,finalize_schema_table,0
};
#ifdef HAVE_DLOPEN
