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## NDB Cluster System Variables 

This section provides detailed information about MySQL server system variables that are specific to NDB Cluster and the NDB  storage engine. For system variables not specific to NDB Cluster, see Section 5.1.8, “Server System Variables” . For general information on using system variables, see Section 5.1.9, “Using System Variables” . 

• ndb_autoincrement_prefetch_sz 

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Determines the probability of gaps in an autoincremented column. Set it to 1  to minimize this. Setting it to a high value for optimization makes inserts faster, but decreases the likelihood of consecutive autoincrement numbers being used in a batch of inserts. 

This variable affects only the number of AUTO_INCREMENT  IDs that are fetched between statements; within a given statement, at least 32 IDs are obtained at a time. 

• ndb_cache_check_time 

## Important 

This variable does not affect inserts performed using INSERT ... SELECT . 

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The number of milliseconds that elapse between checks of NDB Cluster SQL nodes by the MySQL query cache. Setting this to 0 (the default and minimum value) means that the query cache checks for validation on every query. 

The recommended maximum value for this variable is 1000, which means that the check is performed once per second. A larger value means that the check is performed and possibly invalidated due to 

