Beefy Boxes and Bandwidth Generously Provided by pair Networks
The stupid question is the question not asked
 
PerlMonks  

Re: Read Some lines in Tera byte file

by ctilmes (Vicar)
on Oct 13, 2010 at 11:12 UTC ( #865058=note: print w/replies, xml ) Need Help??


in reply to Read Some lines in Tera byte file

Displaying/buffering huge text files discusses some index techniques to speed up picking random lines out of a huge file.

The OP in that thread was able to index a 100MB file with ~6 million lines in seconds and pick out random lines in milliseconds by pre-indexing every 1000 lines.

If your 1TB file had avg 80 characters per line, you'd have 13 billion lines. If you indexed every 1000 lines, you could index 13 million lines. At 8 bytes per index point, that would be 100MB for the index.

You pre-index by reading the entire file, and every 1000 lines, write the file position to your index file.

Then, for example, to find line 12345, you divide that by 1000, and read the 12'th index position in the index (12*8). Then seek to that position in the big file and start reading. After 345 lines you're at your position.

You can tune the 1000 to trade off speed and space.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://865058]
help
Chatterbox?
[Corion]: GrandFather: Yeah, I'm currently in the same situation - I get DOM node IDs from Chrome, except that they vanish at some point in time, or event, or whatever. My current workaround is to re-fetch the node IDs all the time, but that is slow

How do I use this? | Other CB clients
Other Users?
Others making s'mores by the fire in the courtyard of the Monastery: (10)
As of 2017-08-24 07:59 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    Who is your favorite scientist and why?



























    Results (365 votes). Check out past polls.

    Notices?