-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi,
I am the author of https://github.com/whilo/hasch Would calling hasch.core/edn-hash satisfy your performance requirements? I tried hard to make the recursion of the protocol performant, but hashing a value is slower than the time needed to write the data to disk for big collections. You should pick a faster message-digest like you suggested, e.g. MD5: (defn ^MessageDigest md5-message-digest [] (MessageDigest/getInstance "md5")) (edn-hash {:foo "Bar" :baz 5} md5-message-digest) You can use the criterium benchmarking snippets in platform.clj to do benchmarks. Object.hashCode() is a lot faster still and caches the result, I am not sure how much overhead the protocol dispatch causes. Note that if some collisions are ok for you, you might find a better tradeoff, since atm. commutative collections like maps and sets are hashed key-value wise and then XOR'd for safety. I am interested in your findings and decision, especially if you pick something else. Christian On 10.08.2015 09:00, Atamert Ölçgen wrote: > Hi, > > I need a way to reduce a compound value, say {:foo "bar"}, into a > number (like 693d9a0698aff95c in hex). I don't necessarily need a > very large hash space, 7 hex digits is good enough for my purposes. > But I need this hash to be consistent between runs and JVM versions > etc. So I guess that rules out standard object hashes. > > I would like to find a sufficiently fast way to do this. I can live > with MD5, but are there faster alternatives (but produce smaller > hashes)? ( clj-digest <https://github.com/tebeka/clj-digest> > provides a nice interface to what Java provides but there are only > usual suspects AFAICS > <http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#MessageDigest> > > ) > > I will be dealing with unordered collections, but it seems hashing > is consistent when the input order is changed: > > user=> (.hashCode {:foo "Bar" :baz 5}) 2040536238 user=> (.hashCode > {:baz 5 :foo "Bar"}) 2040536238 > > > (It even gave the same hash code in different runs.) > > I will use these hashes to build index tables. My data, that > contains these things I hash is a set. I will store this as an > ordered set and keep an index pointing to where records from this > hash to that hash lives. This is all Clojure, but I can't keep all > my data in memory. (So Clojure's persistent data structures is out > of the picture. life would've been much simpler if I could.) > > Thanks for reading. Any insight is appreciated. > -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJVyJ3vAAoJEKel+aujRZMkbhMIAJ61DGUWM9JoN/JcIxvh2Jph VohlWbr1yw69D+x4guGOk5AXUh7HMAkmlbuc+YRRnYqGhZtc3r/6C/d/aa5faBAh NdIeDa8yNHTAuYERDktfviy+q5a/blJRdvIIe7ntyjpDZyd2gD1AwUGYOKctXipS wMPan7v7yPfPlFfnl+VVXfP8yx/LWyZbwfu0Ugv2B2NhvqPMu8joyondOz7GPcLd P7EgpIrvfQAElA4c4+UB0BEeJkn+fnpYF3QLJIy5oQny5QwbVtxgVuUNES8EolYl HkpFY1ECV/M65fvP6wrcYPihuphSYQoPkfY4ZQfzWCq9mo+3Aj1Jq2u7QfG9HxM= =1UE6 -----END PGP SIGNATURE----- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
