[MDEV-8112] Port no slave left behind into 10.2bb-10.2-mdev8112

This patch implements master throttling based on slave lag, aka no slave left behind.
The core feature works as follows:
1) The semi-sync-reply is ammended to also report back SQL-thread position (aka exec position)
2) Transactions are not removed from the "active-transaction-list"
   in the semi-sync-master plugin until atleast one slave has reported
   that it has executed this transaction. the slave lag can then
   be estimated by calculating how long the oldest transaction has been
   lingering in the active-transaction-list.
3) client-threads are forced to wait before commit until slave lag has decreased to acceptable value.

The following variables are introduced on master:
1. rpl_semi_sync_master_max_slave_lag (global)
2. rpl_semi_sync_master_slave_lag_wait_timeout (session)

The following status variables are introduced on master:
1. rpl_semi_sync_master_slave_lag_wait_sessions
2. rpl_semi_sync_master_estimated_slave_lag
3. rpl_semi_sync_master_trx_slave_lag_wait_time
4. rpl_semi_sync_master_trx_slave_lag_wait_num
5. rpl_semi_sync_master_avg_trx_slave_lag_wait_time

The following variables are introduced on slave:
1. rpl_semi_sync_slave_lag_enabled (global)

In addition to this, 2 optimizations that decreases overhead of semi-sync is introduced.
1) the idea of this is that if when a slave should send and transaction,
   it checks if it should be semi-synced, but rather
   than semi-sync:ing each transaction (which is done currently) the code
   will skip semi-syncing transaction if there already is newer transactions
   committed. But, since this can mean that semi-syncing is delayed indefinitely
   a cap is set using 2 new master variables:
   1. rpl_semi_sync_master_max_unacked_event_bytes (global)
   2. rpl_semi_sync_master_max_unacked_event_count (global)
2) rpl_semi_sync_master_group_commit which makes the semi-sync
   plugin only semi-sync the last transaction in a group commit.

1 files changed, 76 insertions, 2 deletions

diff --git a/sql/rpl_handler.cc b/sql/rpl_handler.cc
index 733af6c61c8..574fc4938a3 100644
--- a/sql/rpl_handler.cc
+++ b/sql/rpl_handler.cc
@@ -23,6 +23,7 @@
 #include "rpl_filter.h"
 #include <my_dir.h>
 #include "rpl_handler.h"
+#include "sql_prepare.h"
 
 Trans_delegate *transaction_delegate;
 Binlog_storage_delegate *binlog_storage_delegate;
@@ -86,6 +87,42 @@ int get_user_var_str(const char *name, char *value,
   return 0;
 }
 
+int set_user_var_int(const char *name,
+                     long long int value,
+                     long long int *old_value)
+{
+  THD* thd= current_thd;
+  bool null_val;
+  user_var_entry *entry=
+      (user_var_entry*) my_hash_search(&thd->user_vars,
+                                       (uchar*) name, strlen(name));
+  if (entry != NULL)
+  {
+    if (old_value != NULL)
+      *old_value= entry->val_int(&null_val);
+  }
+
+  Ed_connection con(thd);
+
+  char buf[256];
+  int res= snprintf(buf, sizeof(buf), "SET @%s=%lld", name, value);
+  if (/* error */ res < 0 ||
+      /* truncated */ res >= sizeof(buf))
+  {
+    return -1;
+  }
+
+  LEX_STRING str;
+  lex_string_set(&str, buf);
+
+  if (con.execute_direct(str))
+  {
+    return -1;
+  }
+
+  return entry == NULL ? 0 : 1;
+}
+
 int delegates_init()
 {
   static my_aligned_storage<sizeof(Trans_delegate), MY_ALIGNOF(long)> trans_mem;
@@ -240,6 +277,17 @@ int Trans_delegate::after_rollback(THD *thd, bool all)
   return ret;
 }
 
+int Trans_delegate::before_commit(THD *thd)
+{
+  int ret= 0, error= 0;
+  Trans_param param;
+  param.flags= 0;
+  param.log_file= 0;
+  param.log_pos= 0;
+  FOREACH_OBSERVER(ret, before_commit, thd, (&param, &error));
+  return error;
+}
+
 int Binlog_storage_delegate::after_flush(THD *thd,
                                          const char *log_file,
                                          my_off_t log_pos,
@@ -364,17 +412,19 @@ int Binlog_transmit_delegate::reserve_header(THD *thd, ushort flags,
 
 int Binlog_transmit_delegate::before_send_event(THD *thd, ushort flags,
                                                 String *packet,
-                                                const char *log_file,
+                                                const char *log_file_path,
                                                 my_off_t log_pos)
 {
   Binlog_transmit_param param;
   param.flags= flags;
 
   int ret= 0;
+  const char* log_file_name= log_file_path != NULL ?
+      log_file_path + dirname_length(log_file_path) : NULL;
   FOREACH_OBSERVER(ret, before_send_event, false,
                    (&param, (uchar *)packet->c_ptr(),
                     packet->length(),
-                    log_file+dirname_length(log_file), log_pos));
+                    log_file_name, log_pos));
   return ret;
 }
 
@@ -404,6 +454,7 @@ int Binlog_transmit_delegate::after_reset_master(THD *thd, ushort flags)
 void Binlog_relay_IO_delegate::init_param(Binlog_relay_IO_param *param,
                                           Master_info *mi)
 {
+  param->mi = mi;
   param->mysql= mi->mysql;
   param->user= mi->user;
   param->host= mi->host;
@@ -530,6 +581,20 @@ int unregister_binlog_relay_io_observer(Binlog_relay_IO_observer *observer, void
 {
   return binlog_relay_io_delegate->remove_observer(observer, (st_plugin_int *)p);
 }
+
+/* get master log pos for a Master_info struct */
+size_t get_master_log_pos(const Master_info* mi,
+                          char *filename_buf, my_off_t *filepos)
+{
+  mysql_mutex_t *mutex= &mi->rli.data_lock;
+
+  mysql_mutex_lock(mutex);
+  *filepos= mi->rli.group_master_log_pos;
+  strncpy(filename_buf, mi->rli.group_master_log_name, FN_REFLEN);
+  mysql_mutex_unlock(mutex);
+  return strnlen(filename_buf, FN_REFLEN);
+}
+
 #else
 int register_binlog_transmit_observer(Binlog_transmit_observer *observer, void *p)
 {
@@ -550,4 +615,13 @@ int unregister_binlog_relay_io_observer(Binlog_relay_IO_observer *observer, void
 {
   return 0;
 }
+
+size_t get_master_log_pos(const Master_info* mi,
+                          char *filename_buf, my_off_t *filepos)
+{
+  *filepos= 0;
+  filename_buf[0]= 0;
+  return 0;
+}
+
 #endif /* HAVE_REPLICATION */