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Beginning with NDB 8.0.16, NDB  uses a background thread to check for metadata changes each ndb_metadata_check_interval  seconds as compared with the MySQL data dictionary. This metadata change detection thread can be disabled by setting ndb_metadata_check  to OFF . The thread is enabled by default. 

• ndb_metadata_check_interval 

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In NDB 8.0.16 and later, NDB runs a metadata change detection thread in the background to determine when the NDB dictionary has changed with respect to the MySQL data dictionary. By default,the interval between such checks is 60 seconds; this can be adjusted by setting the value of ndb_metadata_check_interval . To enable or disable the thread, use ndb_metadata_check . 

• ndb_metadata_sync 

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Setting this variable causes the change monitor thread to override any values set for ndb_metadata_check  or ndb_metadata_check_interval , and to enter a period of continuous change detection. When the thread ascertains that there are no more changes to be detected, it stalls until the binary logging thread has finished synchronization of all detected objects. 

