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).
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