sending multiple metrics in a packet

[ct16k]

While looking for a quick and easy way to send some nginx data to statsd I came upon this module and while it's doing its job properly, there is one thing that was bothering me: for each configured metric it would generate a separate UDP packet. This would mean that when used in a relatively large farm with multiple vhosts, each with multiple metrics defined, it would generate a flurry of packets, even when not under heavy load, that would hammer the statsd service. One obvious solution to this was to combine multiple metrics in a single packet, and the following patch tries to do just that.

--- ngx_http_statsd.c.orig  2015-11-02 22:07:22.736000288 +0000
+++ ngx_http_statsd.c   2015-11-02 22:20:44.615986241 +0000
@@ -18,7 +18,7 @@
 #define STATSD_TYPE_COUNTER    0x0001
 #define STATSD_TYPE_TIMING  0x0002

-#define STATSD_MAX_STR 256
+#define STATSD_MAX_STR 1432

 #define ngx_conf_merge_ptr_value(conf, prev, default)                  \
    if (conf == NGX_CONF_UNSET_PTR) {                                   \
@@ -235,7 +235,8 @@
 ngx_int_t
 ngx_http_statsd_handler(ngx_http_request_t *r)
 {
-    u_char                    line[STATSD_MAX_STR], *p;
+    u_char                    startline[STATSD_MAX_STR], *p, *line;
+    size_t                    togo;
     const char *              metric_type;
     ngx_http_statsd_conf_t   *ulcf;
    ngx_statsd_stat_t        *stats;
@@ -262,6 +263,8 @@
    }

    stats = ulcf->stats->elts;
+   line = startline;
+   togo = STATSD_MAX_STR;
    for (c = 0; c < ulcf->stats->nelts; c++) {

        stat = stats[c];
@@ -287,13 +290,26 @@

        if (metric_type) {
            if (ulcf->sample_rate < 100) {
-               p = ngx_snprintf(line, STATSD_MAX_STR, "%V:%d|%s|@0.%02d", &s, n, metric_type, ulcf->sample_rate);
+               p = ngx_snprintf(line, togo, "%V:%d|%s|@0.%02d\n", &s, n, metric_type, ulcf->sample_rate);
            } else {
-               p = ngx_snprintf(line, STATSD_MAX_STR, "%V:%d|%s", &s, n, metric_type);
+               p = ngx_snprintf(line, togo, "%V:%d|%s\n", &s, n, metric_type);
+           }
+           if (p - line >= togo) {
+               if (line != startline) {
+                   ngx_http_statsd_udp_send(ulcf->endpoint, startline, line - startline - sizeof(char));
+                   c--;
+               }
+               line = startline;
+               togo = STATSD_MAX_STR;
+           } else {
+               togo -= p - line;
+               line = p;
            }
-           ngx_http_statsd_udp_send(ulcf->endpoint, line, p - line);
        }
    }
+   if (togo < STATSD_MAX_STR) {
+       ngx_http_statsd_udp_send(ulcf->endpoint, startline, line - startline - sizeof(char));
+   }

     return NGX_OK;
 }