[jira] [Created] (TS-4149) Add milestone for activity before TS_EVENT_HTTP_SSN_START

["Scott Beardsley (JIRA)" <ji...@apache.org>]

Scott Beardsley created TS-4149:
-----------------------------------

             Summary: Add milestone for activity before TS_EVENT_HTTP_SSN_START
                 Key: TS-4149
                 URL: https://issues.apache.org/jira/browse/TS-4149
             Project: Traffic Server
          Issue Type: Improvement
            Reporter: Scott Beardsley


I ran into a pretty big performance issue in a plugin when it created a mutex in the TS_EVENT_HTTP_SSN_START hook. This caused a significant delay in processing the request. It ended up delaying sending the request to the origin by between 50 and 100ms at the 75%+ percentile! Here is a sample plugin which illustrates the problem:

{noformat}
#include <ts/ts.h>
#include <cstddef>

int globalHandler(TSCont continuation, TSEvent event, void * data) {
        TSHttpSsn session = static_cast< TSHttpSsn >(data);
        TSHttpSsnReenable(session, TS_EVENT_HTTP_CONTINUE);
        return 0;
}

void TSPluginInit(int argc, const char * * argv) {
        TSPluginRegistrationInfo info;
        info.plugin_name = const_cast< char * >(PLUGIN_TAG);
//      If we create a Mutex here there is huge, unaccounted for TTFB latency
      TSCont continuation = TSContCreate(globalHandler, TSMutexCreate());
//      the following will "fix" this problem assuming you don't actually need the mutex
//        TSCont continuation = TSContCreate(globalHandler, NULL);
        TSHttpHookAdd(TS_HTTP_SSN_START_HOOK, continuation);
}
{noformat}

What is also bad about this performance problem is that it is not visible in any of the milestone metrics including ttms. It shows up as a delay between in TTFB on the client side. It caused a lot of confusion to not be able to see the latency in slow logs, thus this request to expose the time spent here to the milestones.



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