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Checkpoint. Generally speaking, when data is saved to disk, it is said that a checkpoint has

been reached. Morę specific to MySQL Cluster, a checkpoint is a point in time where all committed

transactions are stored on disk. With regard to the NDB storage engine, there are twD types of

checkpoints which work together to ensure that a consistent viewof the cluster's data is maintained.

These are shown in the following list:

•    Local Checkpoint (LCP): This is a checkpoint that is specific to a single node; how5ver, LCPs take

place for all nodes in the cluster morę or less concurrently. An LCP involves saving all of a node's

data to disk, and so usually occurs every few minutes. The precise interval varies, and depends upon

the amount of data stored by the node, the level of cluster activity, and other factors.

•    Global Checkpoint (GCP): A GCP occurs every fewseconds, when transactions for all nodes are

synchronized and the redo-log is flushed to disk.

For morę information about the files and directories created by local checkpoints and global

checkpoints, see MySQL Cluster Data Node FileSystemDir Files.