Re: Block at a time ...

>> This is one of the more-or-less solved problems in Unix/Linux. Ext*
>> file systems have a "reserve" usually of 10% of the disk space that
>> nobody except root can use. It's not for root, it's because with 10%
>> of the disk free, you can almost always do a decent job of allocating
>> contiguous blocks and get good performance. Unless Postgres has some
>> weird problem that Linux has never seen before (and that wouldn't be
>> unprecedented...), there's probably no need to fool with
>> file-allocation strategies.
>>
>> Craig
>
> Its fairly easy to break. Just do a parallel import with say, 16
> concurrent tables being written to at once. Result? Fragmented tables.

Delayed allocation (ext4, XFS) helps a lot for concurrent writing at a
medium-high rate (a few megabytes per second and up) when lots of data can
sit in the cache and be flushed/allocated as big contiguous chunks. I'm
pretty sure ext4/XFS would pass your parallel import test.

However if you have files like tables (and indexes) or logs that grow
slowly over time (something like a few megabytes per hour or less), after
a few days/weeks/months, horrible fragmentation is an almost guaranteed
result on many filesystems (NTFS being perhaps the absolute worst).