Re^2: Further optimize usage of SDBM

Yes, I did profile it with Devel::DProf. Sdbm is not the biggest concern, but maybe the only one left optimizable as it is the last really accessing the disk...

Does sdbm really "re-hash (my) key into an internal key."?? The data I am hashing is about 300bytes and I did the hashing to reduce data while getting a (quite) unique key... My understanding was that sdbm would 1:1 use the supplied data as key, but if it really hashes it - I would revert to feeding it the original.. Are you sure?

What about the "feed the data sorted"? Is there any advantage in doing so?

And what about reducing pagesize? Ever tried?? (and can I anticipate what sdbm hashes it to? Sorting senseless??)

Comment on Re^2: Further optimize usage of SDBM_File

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Re^3: Further optimize usage of SDBM_File by samtregar (Abbot) on Jun 14, 2007 at 21:06 UTC
Does sdbm really "re-hash (my) key into an internal key."?? The data I am hashing is about 300bytes and I did the hashing to reduce data while getting a (quite) unique key... My understanding was that sdbm would 1:1 use the supplied data as key, but if it really hashes it - I would revert to feeding it the original.. Are you sure? How could it implement a hash table without hashing the keys? I'm no SDBM expert, but this leads me to believe my guess is correct: http://www.partow.net/programming/hashfunctions/#SDBMHashFunction I can't answer your more specific performance questions. I doubt anyone can, with the possible exception of the people who wrote SDBM. I suggest you setup some benchmarks and try it! -sam	[reply]

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Re^3: Further optimize usage of SDBM_File
by samtregar (Abbot) on Jun 14, 2007 at 21:06 UTC

Does sdbm really "re-hash (my) key into an internal key."?? The data I am hashing is about 300bytes and I did the hashing to reduce data while getting a (quite) unique key... My understanding was that sdbm would 1:1 use the supplied data as key, but if it really hashes it - I would revert to feeding it the original.. Are you sure?

How could it implement a hash table without hashing the keys? I'm no SDBM expert, but this leads me to believe my guess is correct:

http://www.partow.net/programming/hashfunctions/#SDBMHashFunction

I can't answer your more specific performance questions. I doubt anyone can, with the possible exception of the people who wrote SDBM. I suggest you setup some benchmarks and try it!

-sam

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