Database Reference
In-Depth Information
checkpoint was being taken). It is possible for an administrator to run this process manu-
ally while the namenode is in safe mode, using the
hdfs dfsadmin -
saveNamespace
command.
This procedure makes it clear why the secondary has similar memory requirements to the
primary (since it loads the
fsimage
into memory), which is the reason that the secondary
needs a dedicated machine on large clusters.
The schedule for checkpointing is controlled by two configuration parameters. The sec-
ondary namenode checkpoints every hour (
dfs.namenode.checkpoint.period
in seconds), or sooner if the edit log has reached one million transactions since the last
checkpoint (
dfs.namenode.checkpoint.txns
), which it checks every minute
(
dfs.namenode.checkpoint.check.period
in seconds).
