Re^2: Bidirectional lookup algorithm? (no redis )

[Anonymous Monk]

See http://redis.io/topics/benchmarks (esp Pitfalls and misconceptions ), its too slow for this problem ( its ipc )

$ redis-benchmark -t set -r 100000 -n 1000000
====== SET ======
  1000000 requests completed in 13.86 seconds
  50 parallel clients
  3 bytes payload
  keep alive: 1

A simple perl program adds 1mil key/value pairs in a hash in in 2.6875 seconds on a laptop from 2006

OP doesn't need concurrency , so redis not needed

[polettix]

Although in the OP there were no specific quality parameters about space/time constraints, my understanding is that space efficiency improvements could come at the expense of (some) speed, hence the suggestion.

Any benchmark should probably consider both aspects.

[BrowserUk]

my understanding is that space efficiency improvements could come at the expense of (some) speed,

You are correct in that. The ultimate desire is to retain (as much of as is possible) the speed of Perl's hashes; whilst reducing the space requirement necessitated by the need for bidi lookup.

My initial brief suggested that a move from O(1) to O(logN) (with a very small constant) lookup time would be acceptable; if a 4:1 (75%) reduction in space/1:4 (400%) increase in capacity (or greater) was achieved.

However, anonymonk is also correct, in that external storage -- whether disk/SSD or remote ram via sockets -- is too slow. A simple test will show that the minimum turnaround time of sending a request to a 'remote' (even where 'remote' equates to the callback address) and retrieving the reply requires 3 times as long as a perl hash loopkup. Even when you completely exclude the actual lookup and have the request and response consist of a single byte each way.

No matter how fast the actual lookup at the remote, adding that constant to it crushes the overall goal.

[polettix]

I see. So, more or less you're left with the thing you were after in the first place - the algorithm. Good luck with that!