I assume you've overridden the system default for 1024 files in ulimit for # of
open files?
I don't see the times you're seeing using this program...though my databases
are empty which probably makes a difference.
I do see the gradual increase in time...I think this is almost all due to the
OS when you try and open thousands of files in one process.
I ran this once to create 25,000 databases
./db 25000
ls -l file* | wc -l
25000
The tested opening them
time ./db 5000
1.602s
time ./db 10000
5.357s
time ./db 15000
11.280s
time ./db 20000
19.570s
time ./db 25000
28.166s
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "sqlite3.h"
int main(int argc,char *argv[])
{
int i,rc;
sqlite3 *db;
for(i=0;i<atoi(argv[1]);++i) {
char name[4096];
sprintf(name,"file%d",i);
rc=sqlite3_open_v2(name,&db,SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_NOMUTEX,NULL);
if (rc != SQLITE_OK) {
printf("%s",sqlite3_errmsg(db));
exit(1);
}
//sqlite3_close(db); // if you close the database it runs a LOT faster. So
I don't think it's sqlite3 causing it.
}
return 0;
}
If you run this you'll see similar behavior
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main(int argc,char *argv[])
{
int i;
int fd;
for(i=0;i<atoi(argv[1]);++i) {
char name[4096];
sprintf(name,"%dfile",i);
fd=open(name,O_RDWR|O_CREAT);
if (fd==-1) perror("open error:");
write(fd,name,strlen(name));
//close(fd); // again it runs a lot faster if you close the file descriptor
each time -- so it's the OS slowing you down.
fsync(fd);
}
return 0;
}
Michael D. Black
Senior Scientist
NG Information Systems
Advanced Analytics Directorate
From: sqlite-users-boun...@sqlite.org [sqlite-users-boun...@sqlite.org] on
behalf of Terry Cumaranatunge [cumar...@gmail.com]
Sent: Friday, September 02, 2011 6:30 AM
To: sqlite-users@sqlite.org
Subject: EXT :[sqlite] sqlite3_open_v2 performance degrades as number of opens
increase
Hello,
We have an application that creates many small databases (over 100K) to be
able to control the size of the database and provide more deterministic
performance. At process startup, it opens many of these databases in a loop
to keep them open for faster transaction response times. The behavior we are
noticing is that the it takes progressively a longer time for each
sqlite3_open_v2 to complete as the number of databases kept
opened increases. These are some of the measurements:
5000 DBs = 3 secs
10000 DBs = 11 secs
15000 DBs = 35 secs
20000 DBs = 75 secs
Many processes can concurrently open 5000 db's at the same time and it takes
about the same time as a single process doing the work. So, it doesn't
appear to be related to the OS related issue with the number of opens.
The open is done as:
sqlite3_open_v2(dbName, db, SQLITE_OPEN_READWRITE | SQLITE_OPEN_NOMUTEX,
NULL)
We are using RHEL 6 with SQLite 3.7.7.1. Each database was created with
journaling mode set to WAL.
Does anyone know why the performance degrades this way and what can be done
to resolve the problem?
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