Fix Bug#25078 by always letting the replication thread on the slave

server to enter InnoDB. This can be made further customizable by the
user if we introduce a new config parameter. This will wait until
config parameters can be easily added.

Approved by:	Marko

handler/ha_innodb.cc

@@ -407,6 +407,23 @@ static SHOW_VAR innodb_status_variables[]= {
 
 /* General functions */
 
+/**********************************************************************
+Returns true if the thread is the replication thread on the slave
+server. Used in srv_conc_enter_innodb() to determine if the thread
+should be allowed to enter InnoDB - the replication thread is treated
+differently than other threads. Also used in
+srv_conc_force_exit_innodb(). */
+
+extern "C"
+ibool
+thd_is_replication_slave_thread(
+/*============================*/
+			/* out: true if thd is the replication thread */
+	void*	thd)	/* in: thread handle (THD*) */
+{
+	return((ibool)(((THD*)thd)->slave_thread));
+}
+
 /**********************************************************************
 Save some CPU by testing the value of srv_thread_concurrency in inline
 functions. */

include/ha_prototypes.h

 #ifndef HA_INNODB_PROTOTYPES_H
 #define HA_INNODB_PROTOTYPES_H
 
+#include "univ.i" /* ulint, uint */
+#include "m_ctype.h" /* CHARSET_INFO */
+
 /* Prototypes for global functions in ha_innodb.cc that are called by
 InnoDB's C-code. */
 
@@ -19,4 +22,17 @@ innobase_convert_string(
 	CHARSET_INFO*	from_cs,
 	uint*		errors);
 
+/**********************************************************************
+Returns true if the thread is the replication thread on the slave
+server. Used in srv_conc_enter_innodb() to determine if the thread
+should be allowed to enter InnoDB - the replication thread is treated
+differently than other threads. Also used in
+srv_conc_force_exit_innodb(). */
+
+ibool
+thd_is_replication_slave_thread(
+/*============================*/
+			/* out: true if thd is the replication thread */
+	void*	thd);	/* in: thread handle (THD*) */
+
 #endif

srv/srv0srv.c

@@ -47,6 +47,7 @@ Created 10/8/1995 Heikki Tuuri
 #include "dict0boot.h"
 #include "srv0start.h"
 #include "row0mysql.h"
+#include "ha_prototypes.h"
 
 /* This is set to TRUE if the MySQL user has set it in MySQL; currently
 affects only FOREIGN KEY definition parsing */
@@ -987,6 +988,17 @@ srv_conc_enter_innodb(
 	srv_conc_slot_t*	slot	  = NULL;
 	ulint			i;
 
+	if (trx->mysql_thd != NULL
+	    && thd_is_replication_slave_thread(trx->mysql_thd)) {
+
+		/* TODO Do something more interesting (based on a config
+		parameter). Some users what to give the replication
+		thread very low priority, see http://bugs.mysq.com/25078
+		This can be done by introducing
+		innodb_replication_delay(ms) config parameter */
+		return;
+	}
+
 	/* If trx has 'free tickets' to enter the engine left, then use one
 	such ticket */
 
@@ -1162,6 +1174,12 @@ srv_conc_force_exit_innodb(
 		return;
 	}
 
+	if (trx->mysql_thd != NULL
+	    && thd_is_replication_slave_thread(trx->mysql_thd)) {
+
+		return;
+	}
+
 	if (trx->declared_to_be_inside_innodb == FALSE) {
 
 		return;