From: Robert Haas Date: Thu, 7 Oct 2010 16:19:03 +0000 (-0400) Subject: Improve WAL reliability documentation, and add more cross-references to it. X-Git-Tag: REL8_3_13~32 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=9cb280213949d7b42cd9260a5344e952245644b5;p=postgresql Improve WAL reliability documentation, and add more cross-references to it. In particular, we are now more explicit about the fact that you may need wal_sync_method=fsync_writethrough for crash-safety on some platforms, including MaxOS X. There's also now an explicit caution against assuming that the default setting of wal_sync_method is either crash-safe or best for performance. --- diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 460fabe7e3..a54b8ba920 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1486,7 +1486,11 @@ SET ENABLE_SEQSCAN TO OFF; Not all of these choices are available on all platforms. The default is the first method in the above list that is supported - by the platform. + by the platform. The default is not necessarily best; it may be + necessary to change this setting, or other aspects of your system + configuration, in order to create a crash-safe configuration, as + discussed in , or to achieve best + performance. The open_* options also use O_DIRECT if available. This parameter can only be set in the postgresql.conf file or on the server command line. diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml index 090a133185..f50869b791 100644 --- a/doc/src/sgml/wal.sgml +++ b/doc/src/sgml/wal.sgml @@ -75,7 +75,9 @@ by unchecking My Computer\Open\{select disk drive}\Properties\Hardware\Properties\Policies\Enable write caching on the disk. Also on Windows, fsync and - fsync_writethrough never do write caching. + fsync_writethrough never do write caching. The + fsync_writethrough option can also be used to disable + write caching on MacOS X. @@ -457,8 +459,10 @@ The parameter determines how PostgreSQL will ask the kernel to force WAL updates out to disk. - All the options should be the same as far as reliability goes, - but it's quite platform-specific which one will be the fastest. + With the exception of fsync_writethrough, which can sometimes + force a flush of the disk cache even when other options do not do so, + all the options should be the same in terms of reliability. + However, it's quite platform-specific which one will be the fastest. Note that this parameter is irrelevant if fsync has been turned off. @@ -515,6 +519,7 @@ irrecoverable data corruption. Administrators should try to ensure that disks holding PostgreSQL's WAL log files do not make such false reports. + (See .)