Re: Async Commit, v21 (now: v22)

+ <para>
+ Asynchronous commit provides different behaviour to setting
+ <varname>fsync</varname> = off, which is a server-wide
+ setting that will alter the behaviour of all transactions,
+ overriding the setting of <varname>synchronous_commit</varname>,
+ as well as risking much wider data loss. With <varname>fsync</varname>
+ = off the WAL written but not fsynced, so data is lost only in case
+ of a system crash. Both WAL and datafiles written within the last
+ few seconds would be at risk, affecting all types of database
+ transactions. The precise number depends upon whether your operating
+ system is configured for automatic filesystem writeback and what the
+ delay is set too; Linux currently defaults to 30 seconds. With
+ asynchronous commit the WAL is not written to disk at all at commit
+ time, so data is lost if there is a database server crash, whether or
+ not the system crashes at the same time.
+ </para>

I think fsync=off also endagers metadata, while synchronous_commit=off
should be perfectly safe as far as the metadata is concerned.
Wouldn't this be worth mentioning as well?

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Florian Weimer <fweimer(at)bfk(dot)de>
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