Description
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:
#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);
}
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.
Attachments
Attachments
Issue Links
- relates to
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TS-4281 Slow log and milestone updates
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- Open
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