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Update file system snapshot docs.

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Bruce Momjian 2005-03-17 15:38:46 +00:00
parent 57fdb2b0d8
commit 28d150d8e9
1 changed files with 12 additions and 9 deletions
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doc/src/sgml/backup.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.58 2005/03/17 05:10:11 momjian Exp $ $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.59 2005/03/17 15:38:46 momjian Exp $
--> -->
<chapter id="backup"> <chapter id="backup">
<title>Backup and Restore</title> <title>Backup and Restore</title>
@ -364,9 +364,11 @@ tar -cf backup.tar /usr/local/pgsql/data
</para> </para>
<para> <para>
If your database is spread across multiple volumes (for example, If your database is spread across multiple file systems there may not
if you are using tablespaces) there may not be any way be any way to obtain exactly-simultaneous frozen snapshots of all
to obtain exactly-simultaneous frozen snapshots of all the volumes. the volumes. For example, if your data files and WAL log on different
file disks, or if tablespaces are on different file systems, it might
not be possible to use snapshots because the snapshots must be simultaneous.
Read your file system documentation very carefully before trusting Read your file system documentation very carefully before trusting
to the consistent-snapshot technique in such situations. The safest to the consistent-snapshot technique in such situations. The safest
approach is to shut down the database server for long enough to approach is to shut down the database server for long enough to
@ -375,11 +377,12 @@ tar -cf backup.tar /usr/local/pgsql/data
<para> <para>
Another option is to use <application>rsync</> to perform a file Another option is to use <application>rsync</> to perform a file
system backup. First, while the database server is running, system backup. This is done by first running <application>rsync</>
run <application>rsync</>, then shut down the database while the database server is running, then shutting down the database
server and perform a second <application>rsync</>, then server just long enough to do a second <application>rsync</>. The
restart the database server. This allows a file system backup to be second <application>rsync</> will be much quicker than the first,
performed with minimal downtime. but will be consistent because the server was down. This method
allows a file system backup to be performed with minimal downtime.
</para> </para>
<para> <para>