Optimization: in the replication slave, we can avoid doing one strlen() per event's execution,

as we already have db_len in Log_event. Only if rewrite_db() changed the db we need a strlen
(so we now do the strlen() in rewrite_db). Plus a test (we had none for --replicate-rewrite-db :( ).


sql/log_event.cc:
  The goal is to get of rid of one strlen() per replication event in slave:
  we don't need to compute strlen(thd->db) as we already have db_len in the event;
  only case where we need to do a strlen() is if rewrite_db() changed the db.
  Note that db_len is always a meaningful value. It's 0 if event's db is 0.
sql/slave.cc:
  rewrite_db now returns the len of the returned db.
  print_slave_db_safe() needn't call rewrite_db() as rewrite_db() is already called by caller.
sql/slave.h:
  declaration updates for slave.cc

3 files changed, 42 insertions, 0 deletions

diff --git a/mysql-test/r/rpl_rewrite_db.result b/mysql-test/r/rpl_rewrite_db.result
new file mode 100644
index 00000000000..2804b98dea1
--- /dev/null
+++ b/mysql-test/r/rpl_rewrite_db.result
@@ -0,0 +1,22 @@
+stop slave;
+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;
+start slave;
+drop database if exists mysqltest1;
+create database mysqltest1;
+use mysqltest1;
+create table t1 (a int);
+insert into t1 values(9);
+select * from mysqltest1.t1;
+a
+9
+show databases like 'mysqltest1';
+Database (mysqltest1)
+mysqltest1
+select * from test.t1;
+a
+9
+drop table t1;
+drop database mysqltest1;
diff --git a/mysql-test/t/rpl_rewrite_db-slave.opt b/mysql-test/t/rpl_rewrite_db-slave.opt
new file mode 100644
index 00000000000..b9cd29e9205
--- /dev/null
+++ b/mysql-test/t/rpl_rewrite_db-slave.opt
@@ -0,0 +1 @@
+"--replicate-rewrite-db=mysqltest1->test"
diff --git a/mysql-test/t/rpl_rewrite_db.test b/mysql-test/t/rpl_rewrite_db.test
new file mode 100644
index 00000000000..4cc8ae4b676
--- /dev/null
+++ b/mysql-test/t/rpl_rewrite_db.test
@@ -0,0 +1,19 @@
+source include/master-slave.inc;
+--disable_warnings
+drop database if exists mysqltest1;
+--enable_warnings
+create database mysqltest1;
+
+use mysqltest1;
+create table t1 (a int);
+insert into t1 values(9);
+select * from mysqltest1.t1;
+sync_slave_with_master;
+show databases like 'mysqltest1'; # should be empty
+select * from test.t1;
+# cleanup
+connection master;
+drop table t1;
+drop database mysqltest1;
+sync_slave_with_master;
+