I want to process data fetched from the MySQL database simultaneously. I pass the data to each thread process:

#include <mysql.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <pthread.h>
#include "thpool.h" // https://github.com/Pithikos/C-Thread-Pool

#define THREADS 10

struct fparam
{
  int id;
  char *data;
};

void process(void *arg)
{
  struct fparam *args = arg;
  // Processing ID and Data here
  printf("%d - %sn", args->id, args->data);
}

int main(int argc, char **argv)
{
  threadpool thpool = thpool_init(THREADS);

  // MySQL connection

  MYSQL_RES *result = mysql_store_result(con);

  int num_fields = mysql_num_fields(result);
  struct fparam items[100]; // 100 is for the representation

  MYSQL_ROW row;
  int i = 0;
  while ((row = mysql_fetch_row(result)))
  {
    items[i].id = atoi(row[0]);
    items[i].data = row[1];
    thpool_add_work(thpool, process, (void *)(&items[i]));
    i++;
  }

  mysql_free_result(result);
  mysql_close(con);

  thpool_wait(thpool);
  thpool_destroy(thpool);

  exit(0);
}

When there are many rows, items gets too big to fit in the memory (not just heap).

How can I limit the number of rows stored in the memory and delete them when they have been processed?

I think a key issue that we do not know if process function is faster or fetching the rows from the database.