C: kinerja pthread, lebih rendah dari single thrad

Saya bingung dengan kinerja kode saya, ketika berhadapan dengan satu thread hanya menggunakan 13 detik, tetapi akan memakan waktu 80 detik. Saya tidak tahu apakah vektor hanya dapat diakses oleh satu utas pada satu waktu, jika demikian kemungkinan besar saya harus menggunakan array struct untuk menyimpan data alih-alih vektor, adakah yang bisa membantu?

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <iterator>
#include <string>
#include <ctime>
#include <bangdb/database.h>
#include "SEQ.h"

#define NUM_THREADS 16

using namespace std;


typedef struct _thread_data_t {
    std::vector<FDT> *Query;
    unsigned long start;
    unsigned long end;
    connection* conn;
    int thread;
} thread_data_t;



void *thr_func(void *arg) {

    thread_data_t *data = (thread_data_t *)arg;
    std::vector<FDT> *Query = data->Query;
    unsigned long start = data->start;
    unsigned long end = data->end;
    connection* conn = data->conn;

    printf("thread %d started %lu -> %lu\n", data->thread, start, end);

    for (unsigned long i=start;i<=end ;i++ )
    {
        FDT *fout = conn->get(&((*Query).at(i)));
        if (fout == NULL)
        {
            //printf("%s\tNULL\n", s);

        }
        else
        {
            printf("Thread:%d\t%s\n", data->thread, fout->data);
        }
    }

    pthread_exit(NULL);
}


int main(int argc, char *argv[])
{

    if (argc<2)
    {
        printf("USAGE: ./seq <.txt>\n");
        printf("/home/rd/SCRIPTs/12X18610_L5_I052.R1.clean.code.seq\n");

        exit(-1);
    }
    printf("%s\n", argv[1]);

    vector<FDT> Query;

    FILE* fpin;
    if((fpin=fopen(argv[1],"r"))==NULL)  {
        printf("Can't open Input file %s\n", argv[1]);
        return -1; 
    }

    char *key = (char *)malloc(36);

    while (fscanf(fpin, "%s", key) != EOF)
    {
        SEQ * sequence = new SEQ(key);

        FDT *fk = new FDT( (void*)sequence, sizeof(*sequence) );

        Query.push_back(*fk);
    }

    unsigned long Querysize = (unsigned long)(Query.size());
    std::cout << "myvector stores " << Querysize << " numbers.\n";



    //create database, table and connection
    database* db = new database((char*)"berrydb");

    //get a table, a new one or existing one, walog tells if log is on or off
    table* tbl = db->gettable((char*)"hg19", JUSTOPEN);

    if(tbl == NULL)
    {
        printf("ERROR:table NULL error");
        exit(-1);
    }

    //get a new connection
    connection* conn = tbl->getconnection();
    if(conn == NULL)
    {
        printf("ERROR:connection NULL error");
        exit(-1);
    }

    cerr<<"begin querying...\n";


    time_t begin, end;
    double duration;
    begin = clock();




    unsigned long ThreadDealSize = Querysize/NUM_THREADS;
    cerr<<"Querysize:"<<ThreadDealSize<<endl;



    pthread_t thr[NUM_THREADS];
    int rc;

    thread_data_t thr_data[NUM_THREADS];

    for (int i=0;i<NUM_THREADS ;i++ )
    {
        unsigned long ThreadDealStart = ThreadDealSize*i;
        unsigned long ThreadDealEnd   = ThreadDealSize*(i+1) - 1;

        if (i == (NUM_THREADS-1) )
        {
            ThreadDealEnd = Querysize-1;
        }

        thr_data[i].conn = conn;
        thr_data[i].Query = &Query;
        thr_data[i].start = ThreadDealStart;
        thr_data[i].end = ThreadDealEnd;
        thr_data[i].thread = i;
    }


    for (int i=0;i<NUM_THREADS ;i++ )
    {
        if (rc = pthread_create(&thr[i], NULL, thr_func, &thr_data[i]))
        {
          fprintf(stderr, "error: pthread_create, rc: %d\n", rc);
          return EXIT_FAILURE;
        }
    }


    for (int i = 0; i < NUM_THREADS; ++i) {
        pthread_join(thr[i], NULL);
    }


    cerr<<"done\n"<<endl;
    end = clock();
    duration = double(end - begin) / CLOCKS_PER_SEC;
    cerr << "runtime:   " << duration << "\n" << endl;

    db->closedatabase(OPTIMISTIC);
    delete db;
    printf("Done\n");


  return EXIT_SUCCESS;
}