The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.
A checkpoint is a point in the transaction log sequence at which all data files have been updated to reflect the information in the log. All data files will be flushed to disk. Refer to Section 28.4, "WAL Configuration", in the documentation for more details about what happens during a checkpoint.
The CHECKPOINT command forces an immediate checkpoint when the command is issued, without waiting for a regular checkpoint scheduled by the system (controlled by the settings in Section 17.5.2, "Checkpoints", in the documentation). CHECKPOINT is not intended for use during normal operation.
If executed during recovery, the CHECKPOINT command will force a restartpoint (see Section 28.4, "WAL Configuration", in the documentation) rather than writing a new checkpoint.
Only superusers can call CHECKPOINT.
The following description applies only to Postgres-XC
In Postrgres-XC, CHECKPOINT is performed at local Coordinator and allthe underlying Datanodes.
The CHECKPOINT command is a Postgres-XC language extension.