I take the file B contents in a list & then for each Supplier No in file B, I iterate the large file A line by line & check if Supplier No is present in the line. If so, I write the line into file C.

You are doing it the wrong way around. You are having to process your entire 200MB fileA, for every line in fileB. That's O(N2).

Guessing your fileB contains 10-digit Supplier No records, that means your processing will end up reading 70,000 * 200MB ~= 14TeraBytes. (14,000GB). Very slow.

Now invert your logic. Place the Supplier Nos from fileB into a hash.

Then read a line from fileA, extract the Supplier No and look to see if it exists in the hash (O(1)), if it does, write a record to fileC.

This way you read fileB once and fileA once. Just 201MB to read from disk, and ~ 70,000x faster.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
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In reply to Re^3: Out of Memory Error : V-Lookup on Large Sized TEXT File by BrowserUk
in thread Out of Memory Error : V-Lookup on Large Sized TEXT File by TheFarsicle

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