Beefy Boxes and Bandwidth Generously Provided by pair Networks
Do you know where your variables are?

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?

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://865058]
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others musing on the Monastery: (6)
As of 2022-08-08 07:03 GMT
Find Nodes?
    Voting Booth?

    No recent polls found