Version History and Performance

The Azure Functions host does not currently populate the application_Version field in Application Insights. This codebase now emits the version in structured logs, but since those logs go to the traces table instead of the requests table, we have to join these tables to determine the version for a given request.

requests
| where timestamp > ago(30d)
| join kind=leftouter
(
    traces
    | where timestamp > ago(30d) and message contains "Executing with version="
    | project operation_Id, version=customDimensions.prop__version
)
on operation_Id
| summarize count(), round(max(duration)), round(min(duration)), round(avg(duration)), round(percentile(duration, 50)), round(percentile(duration, 95)), round(stdev(duration)) by tostring(version), name, success
| order by version

version	name	success	count_	max_duration	min_duration	avg_duration	percentile_duration_50	percentile_duration_95	stdev_duration
2.0.2.0	Monitor	TRUE	250	3870	1010	1260	1185	1669	283
2.0.2.0	Monitor	FALSE	26	2406	129	882	523	2348	730
2.0.1.1	Monitor	TRUE	238	6322	1285	1851	1690	2854	638
2.0.1.0	Monitor	TRUE	1280	4995	1388	1726	1635	2145	381
2.0.0.2	Monitor	TRUE	2428	11075	990	1294	1167	2040	496
	Monitor	TRUE	2273	10624	1023	1511	1316	2914	625
	Monitor	FALSE	1	638	638	638	638	638	0

v2.0.2.0

This version removed the state table, retrieving new comments on the basis of the last execution time instead, available from the TimerTrigger object, with a configurable slack (defaults to 15 seconds). Wanted to avoid doing it this way, but this is more than adequate. Comments may be missed if the function is paused or errors out (e.g. Reddit API errors), but that hasn't been an issue thus far. If the state table is needed for something else in the future, this may be worth revisiting.

There were a number of errors because the deployment was pushed with a bug regarding the name for the configurable slack variable. After correcting that, the performance has again trended downward.

v2.0.1.1

This version made a minor change, accessing the state table query result directly, instead of through a dictionary. Slight regression in performance.

v2.0.1.0

There was a major performance regression with this version. The cost of extra comments being processed was less than the cost of keeping track of the last update time.

v2.0.0.1

User initialization is defered until necessary, and tables are bound to the function call.

requests | where timestamp > datetime(2018-05-23 2:43:00) | summarize count(), round(max(duration)), round(min(duration)), round(avg(duration)), round(percentile(duration, 50)), round(percentile(duration, 95)), round(stdev(duration)) by name, success

Currently filtering by the timestamp of the last update to analyze the performance impact of this version.

name	success	count_	max_duration	min_duration	avg_duration	percentile_duration_50	percentile_duration_95	stdev_duration
Monitor	TRUE	660	6548	1023	1368	1230	2159	529

The average execution time has gone down by about 14%. The 95th percentile sees a more generous reduction of 29%.

v2.0.0.0

The initial v2.0.0 version on GitHub is ported largely unchanged from v1.1.0, which was a C# .NET Framework Console Application. It was using the RedditSharp listing stream to obtain new Reddit comments to the subreddit in question ad infinitum. That method won't work for an Azure Function, so this initial version simply takes the most recent page of comments (25) each invocation. There are issues with this approach (e.g. if more than 25 comments are posted to the subreddit in that timeframe, it will miss some), and isn't intended as a long-term solution.

There is no logic at the moment to handle exceptions, but it's been very stable. Over 1,300 invocations (4.5 days), there has been 1 failure—the first one. It failed because I set up continuous integration and started the function before updating the application settings.

Using the following Application Insights query, here is the performance of this first version.

requests | where timestamp > ago(30d) | summarize count(), round(max(duration)), round(min(duration)), round(avg(duration)), round(percentile(duration, 50)), round(percentile(duration, 95)), round(stdev(duration)) by name, success

name	success	count_	max_duration	min_duration	avg_duration	percentile_duration_50	percentile_duration_95	stdev_duration
Monitor	TRUE	1304	10624	1110	1583	1338	3032	685
Monitor	FALSE	1	638	638	638	638	638	0