Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.
Write-Ahead Logging (WAL) puts a checkpoint in the transaction log every so often. (To adjust the automatic checkpoint interval, see the run-time configuration options checkpoint_segments and checkpoint_timeout.) The CHECKPOINT command forces an immediate checkpoint when the command is issued, without waiting for a scheduled checkpoint.
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 Chapter 28 for more information about the WAL system.
If executed during recovery, the CHECKPOINT command will force a restartpoint rather than writing a new checkpoint.
Only superusers can call CHECKPOINT. The command is not intended for use during normal operation.
Note: The following description applies only to Postgres-XC
In Postrgres-XC, CHECKPOINT is performed at local Coordinator and allthe underlying Datanodes.