CQLSSTableWriter memory usage for compound primary key

[Xu Zhongxing <xu...@163.com>]

When using CQLSSTableWriter to write a table with compound primary key, if the cluster key is identical for a huge amount of records, the sync() method is never called, and the memory usage keeps growing until the memory is exhausted. 


Could the code be improved to do sync() even when there is no new row is created? The relevant code is in SSTableSimpleUnsortedWriter.java and AbstractSSTableSimpleWriter.java. I am new to the code and cannot produce a reasonable patch for now.


The problem can be reproduced by the following test case:


import org.apache.cassandra.io.sstable.CQLSSTableWriter;
import org.apache.cassandra.exceptions.InvalidRequestException;

import java.io.IOException;
import java.util.UUID;

class SS {
    public static void main(String[] args) {
        String schema = "create table test.t (x uuid, y uuid, primary key (x, y))";


        String insert = "insert into test.t (x, y) values (?, ?)";
        CQLSSTableWriter writer = CQLSSTableWriter.builder()
            .inDirectory("/tmp/test/t")
            .forTable(schema).withBufferSizeInMB(32)
            .using(insert).build();

        UUID id = UUID.randomUUID();
        try {
            for (int i = 0; i < 50000000; i++) {
                UUID id2 = UUID.randomUUID();
                writer.addRow(id, id2);
            }

            writer.close();
        } catch (Exception e) {
            System.err.println("hell");
        }
    }
}