Michael Renner wrote: > Hi, > > the comment WRT WAL recovery and FS journals [1] is a bit misleading in > it's current form. > > First, none of the general purpose filesystems I've seen so far do data > journalling per default, since it's a huge performance penalty, even for > non-RDBMS workloads. The feature you talk about is ext3 specific (and > should be pointed out as such) and only disables write ordering, meaning > that metadata and file content updates are not synchronized.
You are right that my docs were misleading. I have improved them by mentioning that it is _data_ flush that as part of journalling that can be a problem, and documented that the mount option listed is ext3-specific, not linux-specific. Updated docs attached. Please let me know if I can improve it some more. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. +
Index: doc/src/sgml/wal.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/wal.sgml,v retrieving revision 1.54 diff -c -c -r1.54 wal.sgml *** doc/src/sgml/wal.sgml 6 Dec 2008 21:34:27 -0000 1.54 --- doc/src/sgml/wal.sgml 10 Dec 2008 11:04:08 -0000 *************** *** 139,151 **** <para> Because <acronym>WAL</acronym> restores database file contents after a crash, it is not necessary to use a ! journaled filesystem; in fact, journaling overhead can ! reduce performance. For best performance, turn off ! <emphasis>data</emphasis> journaling as a filesystem mount ! option, e.g. use <literal>data=writeback</> on Linux. ! Meta-data journaling (e.g. file creation and directory ! modification) is still desirable for faster rebooting after ! a crash. </para> </tip> --- 139,151 ---- <para> Because <acronym>WAL</acronym> restores database file contents after a crash, it is not necessary to use a ! journaled filesystem for reliability. In fact, journaling ! overhead can reduce performance, especially if journaling ! causes file system <emphasis>data</emphasis> to be flushed ! to disk. Fortunately, data flushing during journaling can ! often be disabled with a filesystem mount option, e.g. ! <literal>data=writeback</> on a Linux ext3 file system. ! Journaled file systems do improve boot speed after a crash. </para> </tip>
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