I want to get data from the database (MySQL) by JPA, I want it sorted by some column value.
So, what is the best practice, to:
OR
Thanks in advance
Data sorting is any process that involves arranging the data into some meaningful order to make it easier to understand, analyze or visualize.
To sort one of the columns in descending order, simply preface the column name with a minus sign '-', as in: table. sortOn("-recipe","y", "mix"); This sorts the table first on recipe in descending order, then on y and mix, in ascending order.
The sorting is a way to arrange elements of a list or array in a certain order. The order may be in ascending or descending order. The numerical and lexicographical (alphabetical) order is a widely used order.
If you are retrieving a subset of all the database data, for example displaying 20 rows on screen out of 1000, it is better to sort on the database. This will be faster and easier and will allow you to retrieve one page of rows (20, 50, 100) at a time instead of all of them.
If your dataset is fairly small, sorting in your code may be more convenient if you want implement a complex sort. Usually this complex sort can be done in SQL
but not as easily as in code.
The short of it is, the rule of thumb is sort via SQL
, with some edge cases to the rule.
In general, you're better off using ORDER BY
in your SQL query -- this way, if there is an applicable index, you may be getting your sorting "for free" (worst case, it will be the same amount of work as doing it in your code, but often it may be less work than that!).
I ran into this very same question, and decided that I should run a little benchmark to quantify the speed differences. The results surprised me. I would like to post my experience with this very sort of question.
As with a number of the other posters here, my thought was that the database layer would do the sort faster because they are supposedly tuned for this sort of thing. @Alex made a good point that if the database already has an index on the sort, then it will be faster. I wanted to answer the question which raw sorting is faster on non-indexed sorts. Note, I said faster, not simpler. I think in many cases letting the db do the work is simpler and less error prone.
My main assumption was that the sort would fit in main memory. Not all problems will fit here, but a good number do. For out of memory sorts, it may well be that databases shine here, though I did not test that. In the case of in memory sorts all of java/c/c++ outperformed mysql in my informal benchmark, if one could call it that.
I wish I had had more time to more thoroughly compare the database layer vs application layer, but alas other duties called. Still, I couldn't help but record this note for others who are traveling down this road.
As I started down this path I started to see more hurdles. Should I compare data transfer? How? Can I compare time to read db vs time to read a flat file in java? How to isolate the sort time vs data transfer time vs time to read the records? With these questions here was the methodology and timing numbers I came up with.
All times in ms unless otherwise posted
All sort routines were the defaults provided by the language (these are good enough for random sorted data)
All compilation was with a typical "release-profile" selected via netbeans with no customization unless otherwise posted
All tests for mysql used the following schema
mysql> CREATE TABLE test_1000000
(
pk bigint(11) NOT NULL,
float_value DOUBLE NULL,
bigint_value bigint(11) NULL,
PRIMARY KEY (pk )
) Engine MyISAM;
mysql> describe test_1000000;
+--------------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------+------+-----+---------+-------+
| pk | bigint(11) | NO | PRI | NULL | |
| float_value | double | YES | | NULL | |
| bigint_value | bigint(11) | YES | | NULL | |
+--------------+------------+------+-----+---------+-------+
First here is a little snippet to populate the DB. There may be easier ways, but this is what I did:
public static void BuildTable(Connection conn, String tableName, long iterations) {
Random ran = new Random();
Math.random();
try {
long epoch = System.currentTimeMillis();
for (long i = 0; i < iterations; i++) {
if (i % 100000 == 0) {
System.out.println(i + " next 100k");
}
PerformQuery(conn, tableName, i, ran.nextDouble(), ran.nextLong());
}
} catch (Exception e) {
logger.error("Caught General Exception Error from main " + e);
}
}
MYSQL Direct CLI results:
select * from test_10000000 order by bigint_value limit 10;
10 rows in set (2.32 sec)
These timings were somewhat difficult as the only info I had was the time reported after the execution of the command.
from mysql prompt for 10000000 elements it is roughly 2.1 to 2.4 either for sorting bigint_value or float_value
Java JDBC mysql call (similar performance to doing sort from mysql cli)
public static void SortDatabaseViaMysql(Connection conn, String tableName) {
try {
Statement stmt = conn.createStatement();
String cmd = "SELECT * FROM " + tableName + " order by float_value limit 100";
ResultSet rs = stmt.executeQuery(cmd);
} catch (Exception e) {
}
}
Five runs:
da=2379 ms
da=2361 ms
da=2443 ms
da=2453 ms
da=2362 ms
Java Sort Generating random numbers on fly (actually was slower than disk IO read). Assignment time is the time to generate random numbers and populate the array
Calling like
JavaSort(10,10000000);
Timing results:
assignment time 331 sort time 1139
assignment time 324 sort time 1037
assignment time 317 sort time 1028
assignment time 319 sort time 1026
assignment time 317 sort time 1018
assignment time 325 sort time 1025
assignment time 317 sort time 1024
assignment time 318 sort time 1054
assignment time 317 sort time 1024
assignment time 317 sort time 1017
These results were for reading a file of doubles in binary mode
assignment time 4661 sort time 1056
assignment time 4631 sort time 1024
assignment time 4733 sort time 1004
assignment time 4725 sort time 980
assignment time 4635 sort time 980
assignment time 4725 sort time 980
assignment time 4667 sort time 978
assignment time 4668 sort time 980
assignment time 4757 sort time 982
assignment time 4765 sort time 987
Doing a buffer transfer results in much faster runtimes
assignment time 77 sort time 1192
assignment time 59 sort time 1125
assignment time 55 sort time 999
assignment time 55 sort time 1000
assignment time 56 sort time 999
assignment time 54 sort time 1010
assignment time 55 sort time 999
assignment time 56 sort time 1000
assignment time 55 sort time 1002
assignment time 56 sort time 1002
C and C++ Timing results (see below for source)
Debug profile using qsort
assignment 0 seconds 110 milliseconds Time taken 2 seconds 340 milliseconds
assignment 0 seconds 90 milliseconds Time taken 2 seconds 340 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 330 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 340 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 330 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 340 milliseconds
assignment 0 seconds 90 milliseconds Time taken 2 seconds 340 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 330 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 340 milliseconds
assignment 0 seconds 100 milliseconds Time taken 2 seconds 330 milliseconds
Release profile using qsort
assignment 0 seconds 100 milliseconds Time taken 1 seconds 600 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 600 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 580 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 590 milliseconds
assignment 0 seconds 80 milliseconds Time taken 1 seconds 590 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 590 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 600 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 590 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 600 milliseconds
assignment 0 seconds 90 milliseconds Time taken 1 seconds 580 milliseconds
Release profile Using std::sort( a, a + ARRAY_SIZE );
assignment 0 seconds 100 milliseconds Time taken 0 seconds 880 milliseconds
assignment 0 seconds 90 milliseconds Time taken 0 seconds 870 milliseconds
assignment 0 seconds 90 milliseconds Time taken 0 seconds 890 milliseconds
assignment 0 seconds 120 milliseconds Time taken 0 seconds 890 milliseconds
assignment 0 seconds 90 milliseconds Time taken 0 seconds 890 milliseconds
assignment 0 seconds 90 milliseconds Time taken 0 seconds 880 milliseconds
assignment 0 seconds 90 milliseconds Time taken 0 seconds 900 milliseconds
assignment 0 seconds 90 milliseconds Time taken 0 seconds 890 milliseconds
assignment 0 seconds 100 milliseconds Time taken 0 seconds 890 milliseconds
assignment 0 seconds 150 milliseconds Time taken 0 seconds 870 milliseconds
Release profile Reading random data from file and using std::sort( a, a + ARRAY_SIZE )
assignment 0 seconds 50 milliseconds Time taken 0 seconds 880 milliseconds
assignment 0 seconds 40 milliseconds Time taken 0 seconds 880 milliseconds
assignment 0 seconds 50 milliseconds Time taken 0 seconds 880 milliseconds
assignment 0 seconds 50 milliseconds Time taken 0 seconds 880 milliseconds
assignment 0 seconds 40 milliseconds Time taken 0 seconds 880 milliseconds
Below is the source code used. Hopefully minimal bugs :)
Java source Note that internal to JavaSort the runCode and writeFlag need to be adjusted depending on what you want to time. Also note that the memory allocation happens in the for loop (thus testing GC, but I did not see any appreciable difference moving the allocation outside the loop)
public static void JavaSort(int iterations, int numberElements) {
Random ran = new Random();
Math.random();
int runCode = 2;
boolean writeFlag = false;
for (int j = 0; j < iterations; j++) {
double[] a1 = new double[numberElements];
long timea = System.currentTimeMillis();
if (runCode == 0) {
for (int i = 0; i < numberElements; i++) {
a1[i] = ran.nextDouble();
}
}
else if (runCode == 1) {
//do disk io!!
try {
DataInputStream in = new DataInputStream(new FileInputStream("MyBinaryFile.txt"));
int i = 0;
//while (in.available() > 0) {
while (i < numberElements) { //this should be changed so that I always read in the size of array elements
a1[i++] = in.readDouble();
}
}
catch (Exception e) {
}
}
else if (runCode == 2) {
try {
FileInputStream stream = new FileInputStream("MyBinaryFile.txt");
FileChannel inChannel = stream.getChannel();
ByteBuffer buffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
//int[] result = new int[500000];
buffer.order(ByteOrder.BIG_ENDIAN);
DoubleBuffer doubleBuffer = buffer.asDoubleBuffer();
doubleBuffer.get(a1);
}
catch (Exception e) {
}
}
if (writeFlag) {
try {
DataOutputStream out = new DataOutputStream(new FileOutputStream("MyBinaryFile.txt"));
for (int i = 0; i < numberElements; i++) {
out.writeDouble(a1[i]);
}
} catch (Exception e) {
}
}
long timeb = System.currentTimeMillis();
Arrays.sort(a1);
long timec = System.currentTimeMillis();
System.out.println("assignment time " + (timeb - timea) + " " + " sort time " + (timec - timeb));
//delete a1;
}
}
C/C++ source
#include <iostream>
#include <vector>
#include <algorithm>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <math.h>
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#define ARRAY_SIZE 10000000
using namespace std;
int compa(const void * elem1, const void * elem2) {
double f = *((double*) elem1);
double s = *((double*) elem2);
if (f > s) return 1;
if (f < s) return -1;
return 0;
}
int compb (const void *a, const void *b) {
if (*(double **)a < *(double **)b) return -1;
if (*(double **)a > *(double **)b) return 1;
return 0;
}
void timing_testa(int iterations) {
clock_t start = clock(), diffa, diffb;
int msec;
bool writeFlag = false;
int runCode = 1;
for (int loopCounter = 0; loopCounter < iterations; loopCounter++) {
double *a = (double *) malloc(sizeof (double)*ARRAY_SIZE);
start = clock();
size_t bytes = sizeof (double)*ARRAY_SIZE;
if (runCode == 0) {
for (int i = 0; i < ARRAY_SIZE; i++) {
a[i] = rand() / (RAND_MAX + 1.0);
}
}
else if (runCode == 1) {
ifstream inlezen;
inlezen.open("test", ios::in | ios::binary);
inlezen.read(reinterpret_cast<char*> (&a[0]), bytes);
}
if (writeFlag) {
ofstream outf;
const char* pointer = reinterpret_cast<const char*>(&a[0]);
outf.open("test", ios::out | ios::binary);
outf.write(pointer, bytes);
outf.close();
}
diffa = clock() - start;
msec = diffa * 1000 / CLOCKS_PER_SEC;
printf("assignment %d seconds %d milliseconds\t", msec / 1000, msec % 1000);
start = clock();
//qsort(a, ARRAY_SIZE, sizeof (double), compa);
std::sort( a, a + ARRAY_SIZE );
//printf("%f %f %f\n",a[0],a[1000],a[ARRAY_SIZE-1]);
diffb = clock() - start;
msec = diffb * 1000 / CLOCKS_PER_SEC;
printf("Time taken %d seconds %d milliseconds\n", msec / 1000, msec % 1000);
free(a);
}
}
/*
*
*/
int main(int argc, char** argv) {
printf("hello world\n");
double *a = (double *) malloc(sizeof (double)*ARRAY_SIZE);
//srand(1);//change seed to fix it
srand(time(NULL));
timing_testa(5);
free(a);
return 0;
}
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