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https://issues.apache.org/jira/browse/TS-4801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15452771#comment-15452771
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John Rushford edited comment on TS-4801 at 8/31/16 5:22 PM:
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Even with that setup, a connection error is a connection error.
markParentDown() increments the failure count for that parent ond only really
makes it unavailable once the fail threshold is met.
was (Author: jrushford):
Even with that setup, a connection error is a connection error.
marParentDown() increments the failure count for that parent ond only really
makes it unavailable once the fail threshold is met.
> Are we marking parents down too aggressively?
> ---------------------------------------------
>
> Key: TS-4801
> URL: https://issues.apache.org/jira/browse/TS-4801
> Project: Traffic Server
> Issue Type: Bug
> Components: Parent Proxy
> Reporter: Leif Hedstrom
> Assignee: Leif Hedstrom
> Fix For: 7.0.0
>
>
> [~jrushford] and I were looking at some code, and found this piece which
> looks suspicious:
> {code}
> } else if (s->current.attempts < s->txn_conf->parent_connect_attempts) {
> s->current.attempts++;
> // Are we done with this particular parent?
> if ((s->current.attempts - 1) %
> s->http_config_param->per_parent_connect_attempts != 0) {
> // No we are not done with this parent so retry
> s->next_action = how_to_open_connection(s);
> DebugTxn("http_trans", "%s Retrying parent for attempt %d, max %"
> PRId64, "[handle_response_from_parent]",
> s->current.attempts,
> s->http_config_param->per_parent_connect_attempts);
> return;
> } else {
> DebugTxn("http_trans", "%s %d per parent attempts exhausted",
> "[handle_response_from_parent]", s->current.attempts);
> // Only mark the parent down if we failed to connect
> // to the parent otherwise slow origin servers cause
> // us to mark the parent down
> if (s->current.state == CONNECTION_ERROR) {
> s->parent_params->markParentDown(&s->parent_result);
> }
> // We are done so look for another parent if any
> next_lookup = find_server_and_update_current_info(s);
> }
> } else {
> // Done trying parents... fail over to origin server if that is
> // appropriate
> DebugTxn("http_trans", "[handle_response_from_parent] Error. No more
> retries.");
> s->parent_params->markParentDown(&s->parent_result);
> s->parent_result.result = PARENT_FAIL;
> next_lookup = find_server_and_update_current_info(s);
> }
> {code}
> Here's my thinking: It seems that if we exhaust parent_connect_attempts
> (which is proxy.config.http.parent_proxy.total_connect_attempts, default 4),
> we end up always marking whatever the current parent is as potentially down.
> This seems wrong, because it might do this even if the number of tries
> against that particular parent has not been exhausted (that is the
> proxy.config.http.parent_proxy.per_parent_connect_attempts setting, tested
> inside the loop).
> Looking at this, it feels that we should either remove that markParentDown()
> entirely, or at a minimum add the same checks as above, i.e.
> {code}
> - s->parent_params->markParentDown(&s->parent_result);
> + if (s->current.state == CONNECTION_ERROR) {
> + s->parent_params->markParentDown(&s->parent_result);
> + }
> {code}
> I'm still doing some more tests, one concern is that it's unclear if the
> earlier comment is correct, and that we can detect the difference between a
> connection failure to parent, vs an origin server response to the parent is
> just being slow (resulting in a timeout and no response to child).
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