Beefy Boxes and Bandwidth Generously Provided by pair Networks
Problems? Is your data what you think it is?
 
PerlMonks  

Re^8: Out of Memory when generating large matrix

by BrowserUk (Pope)
on Mar 08, 2018 at 02:43 UTC ( #1210496=note: print w/replies, xml ) Need Help??


in reply to Re^7: Out of Memory when generating large matrix
in thread Out of Memory when generating large matrix

I have a very similar, before-the-dawn-of-time story -- that I'm sure I've mentioned here before and probably in response to a previous sundial "system sort" solution.

(From long ago memory, so the details my be fuzzy.) 60 million records sorted on 7(or 9) keys taking 2 weeks on twin PDP-11/60s.

Reverse the order of the keys reduced the total time to (I think) less than a day.

The reason: the way the records were stored, the original key order meant doing a seek for every next record, and for almost every sub sort.

Reversing the keys meant the first pass read the records sequentially. Having grouped records by that key, subsequent subsorts tended to only reorder within a small group of records that tended to be close to each other; hence far less disk/memory cache misses.

Another big timesaver that happened before the big final mergesort, was to arrange for temporary spill files to be written to "the other" diskpack, to whichever disk pack the file being processed was on. It applied to pretty much every process, and cut most of their run times in half.

It hard to believe now that in my working lifetime it could have taken a month (before both changes) to sort 60million records. (That was "big data" back then :) )

It's like something out of a Victorian novel where they describe it taking 3 days from London to Bath and 10 days to York.


With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority". The enemy of (IT) success is complexity.
In the absence of evidence, opinion is indistinguishable from prejudice. Suck that fhit
  • Comment on Re^8: Out of Memory when generating large matrix

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1210496]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others wandering the Monastery: (7)
As of 2018-08-17 12:50 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    Asked to put a square peg in a round hole, I would:









    Results (178 votes). Check out past polls.

    Notices?