--- a/src/event/ngx_event_pipe.c
+++ b/src/event/ngx_event_pipe.c
@@ -531,6 +531,12 @@ ngx_event_pipe_write_to_downstream(ngx_e
             } else if (!p->cachable && p->in) {
                 cl = p->in;
 
+                ngx_log_debug3(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                               "pipe write buf ls:%d %p %z",
+                               cl->buf->last_shadow,
+                               cl->buf->pos,
+                               cl->buf->last - cl->buf->pos);
+
                 if (cl->buf->recycled
                     && cl->buf->last_shadow
                     && bsize + cl->buf->last - cl->buf->pos > p->busy_size)

--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -1310,6 +1310,9 @@ ngx_http_fastcgi_input_filter(ngx_event_
 
         ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0, "input buf #%d", b->num);
 
+        ngx_log_debug2(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "input buf %p %z", b->pos, b->last - b->pos);
+
 
         if (f->pos + f->length < f->last) {
 
@@ -1350,6 +1353,9 @@ ngx_http_fastcgi_input_filter(ngx_event_
         b->shadow = buf;
         b->last_shadow = 1;
 
+        ngx_log_debug2(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "input buf last %p %z", b->pos, b->last - b->pos);
+
         return NGX_OK;
     }