WL#2269 Enable query cache for NDB

- Added a thread that fetches commit_count for open tables. This
will mean that NDB will not have to be contacted for every use of a cached query. 


sql/ha_ndbcluster.cc:
  Added a thread that periodically will fetch commit_count 
  for open tables and store that value in share. 
  The commit count value is then used when query cache 
  asks if a cached query can be used. 
  The thread activation interval is regulated by the 
  config variable ndb_cache_check_time, it's default value is 0
  which means that NDB is contacted every time a cached query is reused.
sql/ha_ndbcluster.h:
  Added commit_count to share
  Added ndb_cache_check_time
sql/mysqld.cc:
  Added config variable ndb_cache_check_time
sql/set_var.cc:
  Added config variable ndb_cache_check_time

1 files changed, 2 insertions, 0 deletions

diff --git a/sql/ha_ndbcluster.h b/sql/ha_ndbcluster.h
index b5cf727ead7..df88afa678a 100644
--- a/sql/ha_ndbcluster.h
+++ b/sql/ha_ndbcluster.h
@@ -38,6 +38,7 @@ class NdbBlob;
 
 // connectstring to cluster if given by mysqld
 extern const char *ndbcluster_connectstring;
+extern ulong ndb_cache_check_time;
 
 typedef enum ndb_index_type {
   UNDEFINED_INDEX = 0,
@@ -59,6 +60,7 @@ typedef struct st_ndbcluster_share {
   pthread_mutex_t mutex;
   char *table_name;
   uint table_name_length,use_count;
+  uint commit_count;
 } NDB_SHARE;
 
 /*