Performance: Implement non-wildcard topic subscription management in MqttClientSessionsManager.

[AlexNik4]

#2174

[AlexNik4]

@dotnet-policy-service agree

[AlexNik4]

While this greatly improves performance for non-wildcard topics at the small cost of another index, there is still the issue of incorrectly excluding clients that care about this topic via wildcard subscriptions at the same time as other clients subscribe without wildcards. Tests pass though.

[AlexNik4]

Ok. I think this version works for all cases. I am getting huge performance improvements when there are many clients subscribing to different non-wildcard topics. In the past 2k messages per second with 10k clients was failing. Now I can get 20k messages per second with 20k clients. This will not improve performance if all the clients are using wildcards. But it should not meaningfully degrade performance in that scenario either.

[AlexNik4]

I can look into unit tests later. Would appreciate some feedback on this. Overall, this is just separating topics with and without wildcards so that we can perform additional optimizations for non wildcard topics.

[chkr1011]

@logicaloud Please have a look at the change and let me know what you think.

[logicaloud]

Looks feasible. @AlexNik4, maybe you could run benchmarks "MessageDeliveryBenchmark", "SubscribeBenchmark", and "UnsubscribeBenchmark" and compare the Before and After to cover other scenarios as well?

So far application message handling was geared towards the "many publishers, few subscribers" scenario (see #1298 and "Other considerations"). Having lower performance for a "many subscribers" scenario is not unexpected and improvements here would be great.

Some random observations:

• The check for wildcards in OnSubscriptionAdded could be avoided by passing a list of MqttSubscription to the method instead of the list of strings. The MqttSubscription contains a TopicHasWildcard flag as well as the topic string. The Subscribe method would need to be modified to collect the MqttSubscription in createSubscriptionResult as addedSubscriptions.
• Should the GetSimpleSubscribedTopics property be called SubscribedSimpleTopics?

[AlexNik4]

@logicaloud
Addressed your comments. I ran the benchmarks and am not seeing any real differences. Everything seems within margin of error:

SubscribeBenchmark

Original

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Subscribe_10000_Topics	288.8 ms	8.68 ms	25.58 ms	3000.0000	1000.0000	51.33 MB

With Changes

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Subscribe_10000_Topics	285.5 ms	7.29 ms	21.49 ms	3000.0000	1000.0000	51.34 MB

MessageDeliveryBenchmark

Original

Method	NumPublishers	NumSubscribedTopicsPerSubscriber	NumSubscribers	NumTopicsPerPublisher	Mean	Error	StdDev	Gen0	Gen1	Allocated
DeliverMessages	1000	5	10	1	480.4 us	9.59 us	20.43 us	13.6719	1.9531	228.66 KB
DeliverMessages	1000	5	10	5	478.3 us	9.47 us	20.97 us	13.6719	1.9531	228.76 KB
DeliverMessages	1000	10	10	1	938.5 us	18.55 us	41.12 us	27.3438	5.8594	459.67 KB
DeliverMessages	1000	10	10	5	925.1 us	18.38 us	45.09 us	27.3438	5.8594	451.22 KB
DeliverMessages	1000	20	10	1	1,849.5 us	36.97 us	92.76 us	54.6875	-	895.78 KB
DeliverMessages	1000	20	10	5	1,861.6 us	37.22 us	103.76 us	54.6875	11.7188	898.5 KB
DeliverMessages	1000	50	10	1	4,782.4 us	94.89 us	241.52 us	132.8125	-	2247.69 KB
DeliverMessages	1000	50	10	5	4,731.9 us	94.43 us	233.42 us	132.8125	46.8750	2233.23 KB
DeliverMessages	10000	5	10	1	603.8 us	12.05 us	27.94 us	13.6719	1.9531	234.84 KB
DeliverMessages	10000	5	10	5	593.9 us	11.82 us	26.18 us	13.6719	3.9063	234.4 KB
DeliverMessages	10000	10	10	1	1,164.1 us	22.59 us	47.15 us	27.3438	5.8594	459.29 KB
DeliverMessages	10000	10	10	5	1,165.0 us	23.19 us	45.23 us	27.3438	3.9063	461.97 KB
DeliverMessages	10000	20	10	1	2,348.2 us	46.93 us	107.83 us	54.6875	11.7188	924.58 KB
DeliverMessages	10000	20	10	5	2,353.1 us	46.76 us	116.46 us	58.5938	11.7188	968.89 KB
DeliverMessages	10000	50	10	1	6,105.9 us	120.60 us	180.50 us	148.4375	23.4375	2421.8 KB
DeliverMessages	10000	50	10	5	6,161.9 us	122.52 us	159.31 us	140.6250	23.4375	2310.38 KB

With Changes

Method	NumPublishers	NumSubscribedTopicsPerSubscriber	NumSubscribers	NumTopicsPerPublisher	Mean	Error	StdDev	Gen0	Gen1	Allocated
DeliverMessages	1000	5	10	1	482.5 us	9.60 us	20.67 us	12.6953	2.9297	213.55 KB
DeliverMessages	1000	5	10	5	475.0 us	9.39 us	21.21 us	12.6953	2.9297	211.04 KB
DeliverMessages	1000	10	10	1	941.9 us	18.69 us	45.50 us	25.3906	5.8594	419.38 KB
DeliverMessages	1000	10	10	5	930.3 us	18.46 us	43.50 us	25.3906	5.8594	418.25 KB
DeliverMessages	1000	20	10	1	1,864.9 us	37.06 us	93.64 us	50.7813	-	828.37 KB
DeliverMessages	1000	20	10	5	1,833.5 us	36.58 us	99.53 us	50.7813	7.8125	831.28 KB
DeliverMessages	1000	50	10	1	4,684.0 us	93.11 us	253.31 us	125.0000	39.0625	2068.47 KB
DeliverMessages	1000	50	10	5	4,769.9 us	94.45 us	240.41 us	125.0000	-	2047.32 KB
DeliverMessages	10000	5	10	1	595.0 us	11.33 us	26.04 us	12.6953	2.9297	216.32 KB
DeliverMessages	10000	5	10	5	595.7 us	11.74 us	19.30 us	13.6719	2.9297	226.41 KB
DeliverMessages	10000	10	10	1	1,159.4 us	23.13 us	45.66 us	25.3906	3.9063	427.29 KB
DeliverMessages	10000	10	10	5	1,158.9 us	22.79 us	49.06 us	25.3906	5.8594	427.56 KB
DeliverMessages	10000	20	10	1	2,313.5 us	46.01 us	96.03 us	50.7813	7.8125	841.08 KB
DeliverMessages	10000	20	10	5	2,297.8 us	45.38 us	101.50 us	50.7813	7.8125	845.53 KB
DeliverMessages	10000	50	10	1	5,971.3 us	114.60 us	200.72 us	125.0000	23.4375	2095.64 KB
DeliverMessages	10000	50	10	5	5,954.5 us	118.53 us	207.59 us	125.0000	31.2500	2099.18 KB

UnsubscribeBenchmark

Original

Method	Mean	Error	StdDev	Gen0	Allocated
Unsubscribe_10000_Topics	277.7 ms	7.66 ms	22.57 ms	3000.0000	48.82 MB

With Changes

Method	Mean	Error	StdDev	Median	Gen0	Allocated
Unsubscribe_10000_Topics	275.8 ms	8.70 ms	25.64 ms	282.6 ms	3000.0000	48.81 MB

[logicaloud]

Looks good to me. Up to @chkr1011 for review but here are some ideas regarding naming of variables that may convey the meaning a bit better.

Instead of _simpleTopicsToSession: _simpleTopicToSessions or _subscriberSessionsBySimpleTopic

Instead of out var sessionsWithSimpleTopics: out var simpleTopicSessions