How to find duplicates from a large data file having ~ 10cr records

Without code supplied it is a bit of a shot in the dark, we used something similar to the below example -
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With your supplied issue, I will do the following -
a) Read the file line by line -
b) Split each line into columns -
c) Extract the value from the first column to perform duplicate check -
d) Check if the value exists in a HashSet -
e) If the value is duplicated in the HashSet, perform your action (like deleting etc.) -
f) If the value is not duplicated, add it to the HashSet.
g) Repeat steps b-f for each line in your file -
h) For Garbage Collection, see below -

The above will only store unique values in memory, minimizing your RAM usage.
If you want to be explicit about garbage collection in your code, you can invoke it using the 'System.gc()' method.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashSet;

public class CheckForDuplicatesInFirstColumn {
    public static void main(String[] args) {
        String filename = "your_file_to_read_from.csv";
        HashSet<String> uniqueValues = new HashSet<>();

        try (BufferedReader br = new BufferedReader(new FileReader(filename))) {
            String line;
            while ((line = br.readLine()) != null) {
                String[] columns = line.split(",");
                // Assuming the first column is the key
                String value = columns[0]; 

                if (uniqueValues.contains(value)) {
                    // Duplicate found, do something here
                    System.out.println("Duplicate found: " + line);
                } else {
                    uniqueValues.add(value);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Invoke garbage collection after processing the file
        //keep in mind that invoking System.gc() does not perform immediate garbage collection as the garbage collection is ultimately up to your JVM and it should be used sparingly.
        System.gc();
    }
}