Re: [pgsql-hackers-win32] Sync vs. fsync during checkpoint

Greg Stark wrote:

> Jan Wieck <JanWieck@Yahoo.com> writes:
> 
>> The whole sync() vs. fsync() discussion is in my opinion nonsense at this
>> point. Without the ability to limit the amount of files to a reasonable number,
>> by employing tablespaces in the form of larger container files, the risk of
>> forcing excessive head movement is simply too high.
> 
> I don't think there was any suggestion of conflating tablespaces with
> implementing a filesystem in postgres.
> 
> Tablespaces are just a database entity that database stored objects like
> tables and indexes are associated to. They group database stored objects and
> control the storage method and location.
> 
> The existing storage mechanism, namely a directory with a file for each
> database object, is perfectly adequate and doesn't have to be replaced to
> implement tablespaces. All that's needed is that the location of the directory
> be associated with the "tablespace" of the object rather than be a global
> constant.
> 
> Implementing an Oracle-style filesystem is just one more temptation to
> reimplement OS services in the database. Personally I think it's an awful
> idea. But even if postgres did it as an option, it wouldn't necessarily have
> anything to do with tablespaces.
> 

Doing this is not just what you call it. In a system with let's say 500 
active backends on a database with let's say 1000 things that are 
represented as a file, you'll need half a million virtual file descriptors.


Jan

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