[TS-657] Wrong logic around read_while_writer configuration

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.1.7
• Component/s: Configuration
• Assignee: Leif Hedstrom
• Reporter: Leif Hedstrom
• Created: 27/Jan/11 23:08
• Updated: 19/Aug/11 01:19
• Resolved: 04/Mar/11 03:55

Description

I think the logic around how we read / use the read_while_writer configuration is wrong. The logic should be to only enable read_while_writer if all these configs are set exactly like this:

CONFIG proxy.config.cache.enable_read_while_writer INT 1
CONFIG proxy.config.http.background_fill_completed_threshold FLOAT 0.0
CONFIG proxy.config.cache.max_doc_size INT 0

This logic is encapsulated in a function

static int
update_cache_config(const char *name, RecDataT data_type, RecData data, void *cookie)
{
  (void) name;
  (void) data_type;
  (void) cookie;
  int new_value = data.rec_int;
  if (new_value) {
    float http_bg_fill;
    IOCORE_ReadConfigFloat(http_bg_fill, "proxy.config.http.background_fill_completed_threshold");
    if (http_bg_fill > 0.0) {
      Note("to enable reading while writing a document, %s should be 0.0: read while writing disabled",
           "proxy.config.http.background_fill_completed_threshold");
      return 0;
    }
    if (cache_config_max_doc_size > 0) {
      Note("to enable reading while writing a document, %s should be 0: read while writing disabled",
           "proxy.config.cache.max_doc_size");
      return 0;
    }
  }
  cache_config_read_while_writer = new_value;
  return 0;
}

But, as far as I can tell, this doesn't take effect unless the configuration is reloaded, e.g.

IOCORE_EstablishStaticConfigInt32(cache_config_read_while_writer, "proxy.config.cache.enable_read_while_writer");
IOCORE_RegisterConfigUpdateFunc("proxy.config.cache.enable_read_while_writer", update_cache_config, NULL);

At least from what I can tell, enabling read_while_writer takes effect even if those other two preconditions aren't satisfied. At least when running ATS from command line (traffic_server).