16.6.5.1. Cluster Backup Concepts
A backup is a snapshot of the database at a given time. The
backup consists of three main parts:
Metadata: the names and
definitions of all database tables
Table records: the data
actually stored in the database tables at the time that
the backup was made
Transaction log: a
sequential record telling how and when data was stored in
the database
Each of these parts is saved on all nodes participating in the
backup. During backup, each node saves these three parts into
three files on disk:
-
BACKUP-backup_id.node_id.ctl
A control file containing control information and
metadata. Each node saves the same table definitions (for
all tables in the cluster) to its own version of this
file.
-
BACKUP-backup_id-0.node_id.data
A data file containing the table records, which are saved
on a per-fragment basis. That is, different nodes save
different fragments during the backup. The file saved by
each node starts with a header that states the tables to
which the records belong. Following the list of records
there is a footer containing a checksum for all records.
-
BACKUP-backup_id.node_id.log
A log file containing records of committed transactions.
Only transactions on tables stored in the backup are
stored in the log. Nodes involved in the backup save
different records because different nodes host different
database fragments.
In the listing above, backup_id
stands for the backup identifier and
node_id is the unique identifier
for the node creating the file.
