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<chapter id="backup">

<title>Backup and Restore</title>

<para>

To make use of this backup, you will need to keep around all the WAL

segment files generatedat or after thestarting time of the backup.

segment files generatedduring and after thefile system backup.

To aid you in doing this, the <function>pg_stop_backup</> function

creates a <firstterm>backup history file</> that is immediately stored

into the WAL archive area. This file is named after the first WAL

segment file that you need to have to make use of the backup. For

example, if the starting WAL file is <literal>0000000100001234000055CD</>

the backup history file will be named something like

<literal>0000000100001234000055CD.007C9330.backup</>. (The second part of

this file name stands for an exact position within the WAL file, and can

ordinarily be ignored.) Once you have safely archived this WAL

segment file, you can delete all archived WAL segments with names numerically

preceding this one. The backup history file is just a small text file.

It contains the label string you gave to <function>pg_start_backup</>, as

well as the starting and ending times of the backup. If you used the

label to identify where the associated dump file is kept, then the

archived history file is enough to tell you which dump file to restore,

should you need to do so.

creates a <firstterm>backup history file</> that is immediately

stored into the WAL archive area. This file is named after the first

WAL segment file that you need to have to make use of the backup.

For example, if the starting WAL file is

<literal>0000000100001234000055CD</> the backup history file will be

named something like

<literal>0000000100001234000055CD.007C9330.backup</>. (The second

number in the file name stands for an exact position within the WAL

file, and can ordinarily be ignored.) Once you have safely archived

the WAL segment files used during the file system backup (as

specified in the backup history file), you can delete all archived

WAL segments with names numerically less. Keep in mind that only

completed WAL segment files are archived, so there will be delay

between running <function>pg_stop_backup</> and the archiving of

all WAL segment files needed to make the file system backup

consistent.

</para>

<para>

The backup history file is just a small text file. It contains the

label string you gave to <function>pg_start_backup</>, as well as

the starting and ending times of the backup. If you used the label

to identify where the associated dump file is kept, then the

archived history file is enough to tell you which dump file to

restore, should you need to do so.

</para>

<para>