--- a/src/http/ngx_http_write_filter.c
+++ b/src/http/ngx_http_write_filter.c
@@ -122,8 +122,9 @@ int ngx_http_write_filter(ngx_http_reque
                                              ngx_http_write_filter_module_ctx);
 
 #if (NGX_DEBUG_WRITE_FILTER)
-    ngx_log_debug(r->connection->log, "write filter: last:%d flush:%d" _
-                  last _ flush);
+    ngx_log_debug(r->connection->log,
+                  "write filter: last:%d flush:%qd size:%qd" _
+                  last _ flush _ size);
 #endif
 
     /* avoid the output if there is no last hunk, no flush point and
@@ -164,6 +165,8 @@ static void *ngx_http_write_filter_creat
 
     conf->buffer_output = NGX_CONF_UNSET;
 
+ngx_log_debug(pool->log, "write conf %08X %08X" _ conf _ conf->buffer_output);
+
     return conf;
 }
 
@@ -178,6 +181,8 @@ static char *ngx_http_write_filter_merge
 
     ngx_conf_size_merge(conf->buffer_output, prev->buffer_output, 1460);
 
+ngx_log_debug(pool->log, "write merge %08X %08X %08X" _ prev _ conf _ conf->buffer_output);
+
     return NULL;
 }