Cdb: a fast, reliable, simple package for creating, reading constant databases • Hacker News Board

Re: Cdb: a fast, reliable, simple package for creating, reading constant databases

#41

Post by geogriffin » Sun, May 11, 2014, 4:03 AM UTC

twic wrote: post #28

zura wrote: post #24

Earlier quoted context omitted.

Any links to theory behind cdb?

I'd be particularly interested to know why there are 256 hashtables, rather than one, or some other number. I don't think i've seen this hybrid trie-hashtable before. I wonder if there's any mileage in using a perfect hash function to build a database like this. It seems suited to the operating model of being slow to build but fast to access.

i second that; if anyone knows why there are 256 hashtables rather than just 1, please speak up. my only guess is that it might be a way to prevent 32-bit int overflow in the C code..

Re: Cdb: a fast, reliable, simple package for creating, reading constant databases

#42

Post by wcummings » Sun, May 11, 2014, 10:32 PM UTC

tantalor wrote: post #19

wcummings wrote: post #16

Weird side-note, when using CDB's from Perl, do not use tie, its painfully unperformant (realized this the hard way)

Indeed the documentation notes this. https://metacpan.org/pod/CDB_File#PERFORMANCE

I was handed code that used tie, took me a while to realize what was killing my perf..

Re: Cdb: a fast, reliable, simple package for creating, reading constant databases

#43

Post by wcummings » Tue, May 20, 2014, 3:55 PM UTC

joshu wrote: post #22

wcummings wrote: post #16

Weird side-note, when using CDB's from Perl, do not use tie, its painfully unperformant (realized this the hard way)

CDB isn't really a DBM.

I was handed code already written using tie