Re: [DOCS] [HACKERS] no universally correct setting for fsync
Folks, This is what I have to replace the current fsync entry in config.sgml. I believe that the note about needing fsync for Warm Standby to work correctly is true, but could someone verify it? = fsync configuration parameter fsync (boolean) If this parameter is on, the PostgreSQL server will try to make sure that updates are physically written to disk, by issuing fsync() system calls or various equivalent methods (see ). This ensures that the database cluster can recover to a consistent state after an operating system or hardware crash. While turning off fsync is often a performance benefit, this can result in unrecoverable data corruption in the event of an unexpected shutdown. Thus it is only advisable to turn off fsync if you can easily recreate your entire database from external data. fsync must be on for WAL archiving to work correctly (see ). In many situations, turning off for noncritical transactions can provide much of the potential performance benefit of turning off fsync, without the attendant risks of data corruption. fsync can only be set in the postgresql.conf file or on the server command line. If you turn this parameter off, also consider turning off . -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-docs mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-docs
Re: [DOCS] [HACKERS] no universally correct setting for fsync
Josh Berkus writes: > This is what I have to replace the current fsync entry in config.sgml. s/unexpected shutdown/system crash/, perhaps. The wording you have suggests that a forced Postgres stoppage produces a problem, which it doesn't. It takes a failure at the OS level or below to cause a problem. > I believe that the note about needing fsync for Warm Standby to work > correctly is true, but could someone verify it? AFAIK that's nonsense. The filesystem state that pg_standby could see will be updated in any case; pg_standby has no direct access to the bits on the platters, any more than Postgres does. regards, tom lane -- Sent via pgsql-docs mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-docs
Re: [DOCS] [HACKERS] no universally correct setting for fsync
On 5/7/10 5:13 PM, Tom Lane wrote: > Josh Berkus writes: >> This is what I have to replace the current fsync entry in config.sgml. > > s/unexpected shutdown/system crash/, perhaps. The wording you have > suggests that a forced Postgres stoppage produces a problem, which it > doesn't. It takes a failure at the OS level or below to cause a > problem. I actually meant "unexpected *system* shutdown", i.e. power-out. A lot of people think "crash" just means kernel dump, whereas a UPS failure or tripped power cord is a lot more likely (except maybe on Windows). Revised: == fsync configuration parameter fsync (boolean) If this parameter is on, the PostgreSQL server will try to make sure that updates are physically written to disk, by issuing fsync() system calls or various equivalent methods (see ). This ensures that the database cluster can recover to a consistent state after an operating system or hardware crash. While turning off fsync is often a performance benefit, this can result in unrecoverable data corruption in the event of an unexpected system shutdown or crash. Thus it is only advisable to turn off fsync if you can easily recreate your entire database from external data. In many situations, turning off for noncritical transactions can provide much of the potential performance benefit of turning off fsync, without the attendant risks of data corruption. fsync can only be set in the postgresql.conf file or on the server command line. If you turn this parameter off, also consider turning off . -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-docs mailing list ([email protected]) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-docs
