[CentOS] ext4 in CentOS 5.6?

John R Pierce pierce at hogranch.com
Wed Jul 6 04:17:24 UTC 2011

On 07/05/11 9:04 PM, Charles Polisher wrote:
> 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.
> http://www.postgresql.org/docs/current/static/storage-file-layout.html
> I suppose there could be exceptions, but I haven't run
> across one personally.

you misread that.

    When a table or index exceeds 1 GB, it is divided into
    gigabyte-sized/segments/. The first segment's file name is the same
    as the filenode; subsequent segments are named filenode.1,
    filenode.2, etc. This arrangement avoids problems on platforms that
    have file size limitations. ...

Each file is no larger than 1GB (by default), but its written and 
expanded as needed, not in any fixed size increment.

> 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.

The wal logs are 16M files, also written sequentially as needed, and 
nearly continuously on a insert/update intensive database.  they are not 
reused, rather, old wal files are deleted (unless you're archiving), and 
new ones are created continuously.

john r pierce                            N 37, W 122
santa cruz ca                         mid-left coast

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