Paul Fox writes:
in looking at the pool on our backup machine yesterday, we got to
wondering... currently the pool has paths like:
/big/backuppc/pool/1/2/3/123456789abcdef0
in our case, this leads to leaf directories which are all about
50K large, mostly containing about 1000 files each. since the
final phase of a path lookup is always a linear search
(correct?), mightn't performance be improved by making one or all
of the intermediate path components "wider", i.e., something
like:
/big/backuppc/pool/1/2/34/123456789abcdef0
unless i'm missing something, just doing this would reduce the
leaf directories to more like 3K or 4K bytes, with fewer than a
hundred entries to search.
i'd think that on a ram-limited system this would reduce disk
activity, at the same time that it would reduce cpu time spent
searching the last directory (on any system). i don't claim to
be an expert, but wouldn't better balance to the tree be better?
Obviously it depends upon the underlying file system.
The change you describe is easy to make (see the function MD52Path()
in BackupPC::Lib). BackupPC_nightly will need some changes too.
However, you will need to do it on a clean install with an empty
pool. If you try the experiment I would be curious about whether
you see any significant performance difference.
Craig
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