Обсуждение: ext3 block size

Wilson A. Galafassi Jr. wrote:

> hello.
> my database size is 5GB. what is the block size recommend?
> thanks
> wilson

Hmm, IMHO this depends more on your IO System
rather than on the DB size.
It doesnt make sense to have a blocksize which your IO System
(HD, Controller...) cannot fetch in one read.
And it also depends on the type of Processing you are doing.
If you will have mostly big tablescans, a big blocksize is good,
whereas if you will be doing lots of Index acess, a lower one
can make more sense.
(And also if you store lots of data in one row).
In general I guess 8K (the default) is ok,
but 16K can make sense.

Regards,
Dani

On Fri, 8 Aug 2003, Dani Oderbolz wrote:

> Wilson A. Galafassi Jr. wrote:
>
> > hello.
> > my database size is 5GB. what is the block size recommend?
> > thanks
> > wilson
>
> Hmm, IMHO this depends more on your IO System
> rather than on the DB size.
> It doesnt make sense to have a blocksize which your IO System
> (HD, Controller...) cannot fetch in one read.
> And it also depends on the type of Processing you are doing.
> If you will have mostly big tablescans, a big blocksize is good,
> whereas if you will be doing lots of Index acess, a lower one
> can make more sense.
> (And also if you store lots of data in one row).
> In general I guess 8K (the default) is ok,
> but 16K can make sense.

But that's confusing postgresql block size with ext3 block size.  Right
now the linux 2.4.x kernel only really understands 4k block size as the
max, due to limitations of architechture (X86 only understands 4k memory
page size, and the max block size of a file system is the max page size of
your architecture.  Now, while Itanium (8k) and Itanium2 (64k) can have
larger page sizes, not much has been done to make the 2.4.x series
kernels use these larger limits on hard drive blocks, and the little bit
of hacking I've found on it makes it look like it's still something that's
being tested, i.e. it's not ready for prime time.

Switching to Postgresql block sizes...

Note that while Postgresql supports larger block sizes, it isn't
tested as much as the 8k block size, so you might want to test it
thorougly before putting it into production.