Checkpoint-opracowanie

Checkpoint. Generally speaking, when data is saved to disk, it is said that a checkpoint has
been reached. More 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 two types of
checkpoints which work together to ensure that a consistent view of 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; however, LCPs take
place for all nodes in the cluster more 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 few seconds, when transactions for all nodes are
synchronized and the redo-log is flushed to disk.
For more information about the files and directories created by local checkpoints and global
checkpoints, see MySQL Cluster Data Node FileSystemDir Files.
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