Jeff Clites writes: > On Jan 15, 2004, at 8:26 PM, Benjamin K. Stuhl wrote: > > >Thus wrate Dan Sugalski: > >>At 10:13 AM -0800 1/13/04, Jeff Clites wrote: > >>>Short version: I was originally going to argue for fully > >>>hierarchical namespaces, identified as above, but after turning this > >>>over in my head for a while, I came to the conclusion that > >>>namespaces are not conceptually hierarchical (especially as used in > >>>languages such as Perl5 and Java, at least), so I'm going to argue > >>>for a single string (rather than an array) as a namespace > >>>identifier. > ... > >Performance-wise, I would guesstimate that it's more-or-less a > >wash between parsing strings and parsing multidimensional keys, > >so as long as we precreate the keys (keep thm in a constant > >table or something), I see no performance issues. > > It turns out that it makes a big difference in lookup times--doing one > hash lookup v. several. I did this experiment using Perl5 (5.8.0): > Create a structure holding 1296 entries, each logically 12 characters > long--either one level of 12 character strings, or 2 levels of 6 > character strings, or 3 levels of 4 character strings, or 4 levels of 3 > character strings, and look up the same item 10 million times. Here is > the time it takes for the lookups: > > 1-level: 14 sec. > 2-level: 20 sec. > 3-level: 25 sec. > 4-level: 32 sec. > > Conclusion: It's faster to do one lookup of a single, longer string > than several lookups of shorter strings. > > Of course, as Uri pointed out, even if we go with hierarchical > namespaces, we could implement these internally as a single-level hash, > behind the scenes, as an implementation detail and optimization.
My two cents: I don't care as long as we can toss symbol tables around as PMCs, and replace symbol tables with different (alternately implemented) PMCs. I think it's possible to do this using a clever ordered hash scheme even if we go one level, but it's something to keep in mind. Luke > JEff >
