[CentOS] ext4 in CentOS 5.6?

Charles Polisher cpolish at surewest.net
Wed Jul 6 04:04:54 UTC 2011

> On 07/05/11 7:10 AM, Charles Polisher wrote:
> > In general and with some simplifiying assumptions, a database
> > consists of statically pre-allocated files. The process of extending
> > the files happens at birth. The relative speed over the lifetime
> > of the database is dominated by raw I/O, not by extending the files.
> thats not even remotely true of many databases.  PostgreSQL, for 
> example, the files are extended as they are updated/inserted, as are the 
> WAL files.

The PostgreSQL wiki seems to say that database tables are
allocated in 1GB extents. In workloads with which I am
familiar, with an RDBMS the extents don't bounce
around all that much, i.e. the vast majority of writes do
not result in a change to the underlying database's storage
allocation. Once in a while a new extent is allocated.
I suppose there could be exceptions, but I haven't run
across one personally.

The "WAL" files you refer to are apparently database
transaction logs. According to the wiki, these too
are allocated in extents (WAL segments) of 16MB each.

I am not persuaded that the point I was making was

Charles Polisher

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