Обсуждение: pgsql: Mention tablespaces as a problem for using file system snapshots.
pgsql: Mention tablespaces as a problem for using file system snapshots.
От
momjian@svr1.postgresql.org (Bruce Momjian)
Дата:
Log Message: ----------- Mention tablespaces as a problem for using file system snapshots. Modified Files: -------------- pgsql/doc/src/sgml: backup.sgml (r2.57 -> r2.58) (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/backup.sgml.diff?r1=2.57&r2=2.58)
momjian@svr1.postgresql.org (Bruce Momjian) writes: > Mention tablespaces as a problem for using file system snapshots. This is a considerable disimprovement, since it replaces an example which is actually relevant to the point with one that isn't necessarily so. And why did you feel a need to remove the previous example anyway? regards, tom lane
Tom Lane wrote: > momjian@svr1.postgresql.org (Bruce Momjian) writes: > > Mention tablespaces as a problem for using file system snapshots. > > This is a considerable disimprovement, since it replaces an example > which is actually relevant to the point with one that isn't necessarily > so. And why did you feel a need to remove the previous example anyway? The text is now: If your database is spread across multiple volumes (for example, if you are using tablespaces) there may not be any way to obtain exactly-simultaneous frozen snapshots of all the volumes. I assume many more people are using tablespaces than moving pg_xlog. You want two examples in that sentence? -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes: > I assume many more people are using tablespaces than moving pg_xlog. I don't believe that premise. Relocating xlog is an essential step for high-performance databases ... using tablespaces isn't. > You want two examples in that sentence? I think the xlog case needs to be mentioned, and I think there needs to be specific reference to a multi-volume situation. "Using tablespaces" doesn't necessarily mean the database is spread across multiple disks. In short, I thought the original wording was better. regards, tom lane
Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > I assume many more people are using tablespaces than moving pg_xlog. > > I don't believe that premise. Relocating xlog is an essential step > for high-performance databases ... using tablespaces isn't. > > > You want two examples in that sentence? > > I think the xlog case needs to be mentioned, and I think there needs to > be specific reference to a multi-volume situation. "Using tablespaces" > doesn't necessarily mean the database is spread across multiple disks. > > In short, I thought the original wording was better. > OK, I broke out the examples into a separate sentence. I also update the rsync mention. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 Index: doc/src/sgml/backup.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/backup.sgml,v retrieving revision 2.58 diff -c -c -r2.58 backup.sgml *** doc/src/sgml/backup.sgml 17 Mar 2005 05:10:11 -0000 2.58 --- doc/src/sgml/backup.sgml 17 Mar 2005 15:26:23 -0000 *************** *** 364,372 **** </para> <para> ! If your database is spread across multiple volumes (for example, ! if you are using tablespaces) there may not be any way ! to obtain exactly-simultaneous frozen snapshots of all the volumes. Read your file system documentation very carefully before trusting to the consistent-snapshot technique in such situations. The safest approach is to shut down the database server for long enough to --- 364,374 ---- </para> <para> ! If your database is spread across multiple file systems there may not ! be any way to obtain exactly-simultaneous frozen snapshots of all ! 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 to the consistent-snapshot technique in such situations. The safest approach is to shut down the database server for long enough to *************** *** 375,385 **** <para> Another option is to use <application>rsync</> to perform a file ! system backup. First, while the database server is running, ! run <application>rsync</>, then shut down the database ! server and perform a second <application>rsync</>, then ! restart the database server. This allows a file system backup to be ! performed with minimal downtime. </para> <para> --- 377,388 ---- <para> Another option is to use <application>rsync</> to perform a file ! system backup. This is done by first running <application>rsync</> ! while the database server is running, then shutting down the database ! server just long enough to do a second <application>rsync</>. The ! second <application>rsync</> will be much quicker than the first, ! but will be consistent because the server was down. This method ! allows a file system backup to be performed with minimal downtime. </para> <para>