Fix for Bug#6148. Only rewind read position in binary log when the

slave SQL thread is started.

mysql-test/r/rpl_start_stop_slave.result

+slave stop;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+slave start;
+stop slave;
+create table t1(n int);
+start slave;
+stop slave io_thread;
+start slave io_thread;
+drop table t1;

mysql-test/t/rpl_start_stop_slave.test

+source include/master-slave.inc;
+
+#
+# Bug#6148 ()
+#
+connection slave;
+stop slave;
+
+# Let the master do lots of insertions
+connection master;
+create table t1(n int);
+let $1=5000;
+disable_query_log;
+while ($1)
+{
+ eval insert into t1 values($1);
+ dec $1;
+}
+enable_query_log;
+save_master_pos;
+
+connection slave;
+start slave;
+sleep 1;
+stop slave io_thread;
+start slave io_thread;
+sync_with_master;
+
+connection master;
+drop table t1;
+save_master_pos;
+
+connection slave;
+sync_with_master;

sql/repl_failsafe.cc

@@ -892,7 +892,8 @@ int load_master_data(THD* thd)
           setting active_mi, because init_master_info() sets active_mi with
           defaults.
         */
-        if (init_master_info(active_mi, master_info_file, relay_log_info_file, 0))
+        if (init_master_info(active_mi, master_info_file, relay_log_info_file, 
+			     0, (SLAVE_IO | SLAVE_SQL)))
           send_error(&thd->net, ER_MASTER_INFO);
 	strmake(active_mi->master_log_name, row[0],
 		sizeof(active_mi->master_log_name));

sql/slave.cc

@@ -137,7 +137,7 @@ int init_slave()
   }
     
   if (init_master_info(active_mi,master_info_file,relay_log_info_file,
-		       !master_host))
+		       !master_host, (SLAVE_IO | SLAVE_SQL)))
   {
     sql_print_error("Failed to initialize the master info structure");
     goto err;
@@ -1616,7 +1616,8 @@ void clear_last_slave_error(RELAY_LOG_INFO* rli)
 
 int init_master_info(MASTER_INFO* mi, const char* master_info_fname,
 		     const char* slave_info_fname,
-		     bool abort_if_no_master_info_file)
+		     bool abort_if_no_master_info_file,
+		     int thread_mask)
 {
   int fd,error;
   char fname[FN_REFLEN+128];
@@ -1630,8 +1631,15 @@ int init_master_info(MASTER_INFO* mi, const char* master_info_fname,
       last time. If this case pos_in_file would be set and we would
       get a crash when trying to read the signature for the binary
       relay log.
+      
+      We only rewind the read position if we are starting the SQL
+      thread. The handle_slave_sql thread assumes that the read
+      position is at the beginning of the file, and will read the
+      "signature" and then fast-forward to the last position read.
     */
-    my_b_seek(mi->rli.cur_log, (my_off_t) 0);
+    if (thread_mask & SLAVE_SQL) {
+      my_b_seek(mi->rli.cur_log, (my_off_t) 0);
+    }
     DBUG_RETURN(0);
   }
 

sql/slave.h

@@ -411,7 +411,8 @@ void init_master_info_with_options(MASTER_INFO* mi);
 void clear_last_slave_error(RELAY_LOG_INFO* rli);
 int init_master_info(MASTER_INFO* mi, const char* master_info_fname,
 		     const char* slave_info_fname,
-		     bool abort_if_no_master_info_file);
+		     bool abort_if_no_master_info_file,
+		     int thread_mask);
 void end_master_info(MASTER_INFO* mi);
 int init_relay_log_info(RELAY_LOG_INFO* rli, const char* info_fname);
 void end_relay_log_info(RELAY_LOG_INFO* rli);

sql/sql_repl.cc

@@ -662,7 +662,8 @@ int start_slave(THD* thd , MASTER_INFO* mi,  bool net_report)
     thread_mask &= thd->lex.slave_thd_opt;
   if (thread_mask)
   {
-    if (init_master_info(mi,master_info_file,relay_log_info_file, 0))
+    if (init_master_info(mi,master_info_file,relay_log_info_file, 0,
+			 thread_mask))
       slave_errno=ER_MASTER_INFO;
     else if (server_id_supplied && *mi->host)
       slave_errno = start_slave_threads(0 /*no mutex */,
@@ -867,7 +868,8 @@ int change_master(THD* thd, MASTER_INFO* mi)
   thd->proc_info = "Changing master";
   LEX_MASTER_INFO* lex_mi = &thd->lex.mi;
   // TODO: see if needs re-write
-  if (init_master_info(mi, master_info_file, relay_log_info_file, 0))
+  if (init_master_info(mi, master_info_file, relay_log_info_file, 0,
+		       thread_mask))
   {
     send_error(&thd->net, ER_MASTER_INFO);
     unlock_slave_threads(mi);