Using Named Pipes

Greenplum Database allows the use of named pipes with gpcrondump and gpdbrestore to back up and restore Greenplum databases. When backing up a database with regular files, the files that contain the backup information are placed in directories on the Greenplum Database segments. If segment hosts do not have enough local disk space available to backup to files, you can use named pipes to back up to non-local storage, such as storage on another host on the network or to a backup appliance.

Backing up with named pipes is not supported if the --ddboost option is specified.

To back up a Greenplum database using named pipes

Run the gpcrondump command with options -K timestamp and --list-backup-files.

This creates two text files that contain the names of backup files, one per line. The file names include the timestamp you specified with the -K timestamp option and have the suffixes _pipes and _regular_files. For example:
```
gp_dump_20150519160000_pipes 
gp_dump_20150519160000_regular_files
```
The file names listed in the _pipes file are to be created as named pipes. The file names in the _regular_files file should not be created as named pipes. gpcrondump and gpdbrestore use the information in these files during backup and restore operations.
Create named pipes on all Greenplum Database segments using the file names in the generated _pipes file.
Redirect the output of each named pipe to the destination process or file object.
Run gpcrondump to back up the database using the named pipes.

To create a complete set of Greenplum Database backup files, the files listed in the _regular_files file must also be backed up.

To restore a database that used named pipes during backup

Direct the contents of each backup file to the input of its named pipe, for example cat filename > pipename, if the backup file is accessible as a local file object.
Run the gpdbrestore command to restore the database using the named pipes.

Parent topic: Parallel Backup with gpcrondump and gpdbrestore

Example

This example shows how to back up a database over the network using named pipes and the netcat (nc) Linux command. The segments write backup files to the inputs of the named pipes. The outputs of the named pipes are piped through nc commands, which make the files available on TCP ports. Processes on other hosts can then connect to the segment hosts at the designated ports to receive the backup files. This example requires that the nc package is installed on all Greenplum hosts.

Enter the following gpcrondump command to generate the lists of backup files for the testdb database in the /backups directory.
```
$ gpcrondump -x testdb -K 20150519160000 --list-backup-files -u /backups
```

View the files that gpcrondump created in the /backup directory:

$ ls -lR /backups
/backups:
total 4
drwxrwxr-x 3 gpadmin gpadmin 4096 May 19 21:49 db_dumps

/backups/db_dumps:
total 4
drwxrwxr-x 2 gpadmin gpadmin 4096 May 19 21:49 20150519

/backups/db_dumps/20150519:
total 8
-rw-rw-r-- 1 gpadmin gpadmin 256 May 19 21:49 gp_dump_20150519160000_pipes
-rw-rw-r-- 1 gpadmin gpadmin 391 May 19 21:49 gp_dump_20150519160000_regular_files

View the contents of the _pipes file.

$ cat /backups/db_dumps/20150519/gp_dump_20150519160000_pipes 
sdw1:/backups/db_dumps/20150519/gp_dump_0_2_20150519160000.gz
sdw2:/backups/db_dumps/20150519/gp_dump_1_3_20150519160000.gz
mdw:/backups/db_dumps/20150519/gp_dump_-1_1_20150519160000.gz
mdw:/backups/db_dumps/20150519/gp_dump_-1_1_20150519160000_post_data.gz

Create the specified named pipes on the Greenplum Database segments. Also set up a reader for the named pipe.
```
gpssh -h sdw1
[sdw1] mkdir -p /backups/db_dumps/20150519/
[sdw1] mkfifo /backups/db_dumps/20150519/gp_dump_0_2_20150519160000.gz
[sdw1] cat /backups/db_dumps/20150519/gp_dump_0_2_20150519160000.gz | nc -l 21000 
[sdw1] exit
```
Complete these steps for each of the named pipes listed in the _pipes file. Be sure to choose an available TCP port for each file.
On the destination hosts, receive the backup files with commands like the following:
```
nc sdw1 21000 > gp_dump_0_2_20150519160000.gz
```

Run gpcrondump to begin the backup:

gpcrondump -x testdb -K 20150519160000 -u /backups

To restore a database with named pipes, reverse the direction of the backup files by sending the contents of the backup files to the inputs of the named pipes and run the gpdbrestore command:

gpdbrestore -x testdb -t 20150519160000 -u /backups

gpdbrestore reads from the named pipes' outputs.