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

1 files changed, 5 insertions, 2 deletions

diff --git a/sql/slave.cc b/sql/slave.cc
index 4ef8715f1e6..d5278e06d8a 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -1032,7 +1032,7 @@ bool net_request_file(NET* net, const char* fname)
 }
 
 
-const char *rewrite_db(const char* db)
+const char *rewrite_db(const char* db, uint *new_len)
 {
   if (replicate_rewrite_db.is_empty() || !db)
     return db;
@@ -1042,7 +1042,10 @@ const char *rewrite_db(const char* db)
   while ((tmp=it++))
   {
     if (!strcmp(tmp->key, db))
+    {
+      *new_len= strlen(tmp->val);
       return tmp->val;
+    }
   }
   return db;
 }
@@ -1056,7 +1059,7 @@ const char *rewrite_db(const char* db)
 
 const char *print_slave_db_safe(const char* db)
 {
-  return (db ? rewrite_db(db) : "");
+  return (db ? db : "");
 }
 
 /*