Tweaking Lighttpd stat() performance with fcgi-stat-accel

If you serve lots of (small) files with Lighttpd you might notice you're not getting the throughput you would expect. Other factors (such as latencies because of the random read patterns ) aside, a real show stopper is the stat() system call, which is a blocking system call ( no parallelism ). Some clever guys thought of a way to solve this : a fastcgi program that does a stat(), so when it returns Lighty doesn't have to wait because the stat information will be in the Linux cache. And in the meanwhile your Lighty thread can do other stuff.
(in Lighty 1.5 there will be a native way for asynchronous stat() calls but for 1.4 this hack works pretty damn well)

This is explained on the HowtoSpeedUpStatWithFastcgi page on the Lighty wiki.

Now, for Netlog we needed to add some http headers ( Cache-Control: max-age, ETag, Expires and Last-Modified ) so we patched up the code a bit to do that, and a bit of other stuff.

Ofcourse this is documented on the FcgiStatAccelWithMoreHttpHeaders page on the Lighty wiki

Have fun !

  Originally written by Fobax.
  Edited by darix to support controlling thread count at runtime. 
  Edited by poison and Dieter_be to support some http headers derived from the files.

  Please do not remove any of the above.
  compile with: 

  $ gcc -lfcgi -lpthread fcgi-stat-accel.c -o fcgi-stat-accel

  fcgi-stat-accel will use the PHP_FCGI_CHILDREN environment variable to set the thread count.

  The default value, if spawned from lighttpd, is 20.

#include "fcgi_config.h"

#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>   
#include "fcgiapp.h"  
#include <string.h>   
#include <sys/types.h>
#include <sys/stat.h> 

#include <stdlib.h>
#include <stdio.h> 

#include "etag.h"
#include "buffer.h"

#define THREAD_COUNT 20

#define FORBIDDEN(stream) \
        FCGX_FPrintF(stream, "Status: 403 Forbidden\r\nContent-Type: text/html\r\n\r\n<h1>403 Forbidden</h1>\n");
#define NOTFOUND(stream, filename) \
        FCGX_FPrintF(stream, "Status: 404 Not Found\r\nContent-Type: text/html\r\n\r\n<h1>404 Not Found</h1>\r\n%s", filename);
#define SENDFILE(stream, filename, headers) \
        FCGX_FPrintF(stream, "%sX-LIGHTTPD-send-file: %s\r\n\r\n", headers, filename);

#define EXPIRATION_TIME (int) 60*60*24*30

int genheaders (char* mybuffer, size_t bufferlen, const char* file)
        char timebuf[32]; //possibly unsafe   
        char lastmodbuf[32]; //possibly unsafe
        char etag[128]; //possibly unsafe
        struct stat statbuf;
        time_t exp;
        time_t lastmod;  
        buffer *etag_raw;
        buffer *etag_ok ;
        //create buffers for Etag
        etag_raw = buffer_init();
        etag_ok = buffer_init();
        // Stat the file
        if (stat (file, &statbuf) != 0)
                return -1;

        // Clear the buffer
        memset (mybuffer, 0, bufferlen);

        // Get the local time
        exp = time (NULL) + EXPIRATION_TIME;
        lastmod = statbuf.st_mtime;

        strftime (timebuf, (sizeof (timebuf) / sizeof (char)) - 1, "%a, %d %b %Y %H:%M:%S GMT", gmtime (&(exp)));
        strftime (lastmodbuf, (sizeof (lastmodbuf) / sizeof (char)) - 1, "%a, %d %b %Y %H:%M:%S GMT", gmtime (&(lastmod)));

        etag_create(etag_raw, &statbuf, ETAG_USE_SIZE);
        etag_mutate(etag_ok, etag_raw);


        snprintf (mybuffer, bufferlen, "Cache-Control: max-age=%d\r\nETag: \%s\r\nExpires: %s\r\nLast-Modified: %s\r\n", EXPIRATION_TIME, etag_ok->ptr, timebuf , lastmodbuf);


        return 0;
static void *doit(void *a){
        FCGX_Request request;
        int rc;
        char *filename;
        char extraheaders[192];
        int r;

        FCGX_InitRequest(&request, 0, FCGI_FAIL_ACCEPT_ON_INTR);

                //Some platforms require accept() serialization, some don't. The documentation claims it to be thread safe
//              static pthread_mutex_t accept_mutex = PTHREAD_MUTEX_INITIALIZER;
//              pthread_mutex_lock(&accept_mutex);
                rc = FCGX_Accept_r(&request);
//              pthread_mutex_unlock(&accept_mutex);

                if(rc < 0)

        //get the filename
                if((filename = FCGX_GetParam("SCRIPT_FILENAME", request.envp)) == NULL){
        //don't try to open directories
                }else if(filename[strlen(filename)-1] == '/'){
        //open the file
                }else if((r = genheaders (extraheaders, 191, filename)) != 0){
                        NOTFOUND(request.out, filename);
        //no error, serve it
                        SENDFILE(request.out, filename, extraheaders);

        return NULL;

int main(void){
        int i,j,thread_count;
        pthread_t* id;
        char* env_val;


        thread_count = THREAD_COUNT;
        env_val = getenv("PHP_FCGI_CHILDREN");
        if (env_val != NULL) {
                j = atoi(env_val);
                if (j != 0) {
                        thread_count = j;

        id = malloc(sizeof(*id) * thread_count);

        for (i = 0; i < thread_count; i++) {
                pthread_create(&id[i], NULL, doit, NULL);

        return 0;  

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