⚡️[RUM-3570] Batch the records for 16ms minimum before processing them

[amortemousque]

Motivation

When recording for Session Replay, MutationRecord objects are batched together (see mutationBatch), then deduplicated on processing (ex: here).

When the same mutation happens continuously on the same element, for example with JS-driven animations, a lot of MutationRecords can be notified by the browser in a very short amount of time, which can significantly inflate the data sent to Datadog, and have a performance impact both on the recorder side and on the player side (see below). Those mutations could be deduplicated if they were batched together.

Changes

Batch the records for 16ms minimum before processing them

Testing

• Local
• Staging
• Unit
• End to end

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I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.65%. Comparing base (b839f8c) to head (28d38d9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2807   +/-   ##
=======================================
  Coverage   93.65%   93.65%           
=======================================
  Files         243      243           
  Lines        7140     7143    +3     
  Branches     1599     1599           
=======================================
+ Hits         6687     6690    +3     
  Misses        453      453           

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[cit-pr-commenter]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	159.49 KiB	159.55 KiB	62 B	+0.04%	✅
Logs	58.02 KiB	58.02 KiB	0 B	0.00%	✅
Rum Slim	108.07 KiB	108.07 KiB	0 B	0.00%	✅
Worker	25.21 KiB	25.21 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base Average Cpu Time (ms)	Local Average Cpu Time (ms)	𝚫
addglobalcontext	0.002	0.002	-0.000
addaction	0.050	0.042	-0.007
adderror	0.052	0.034	-0.017
addtiming	0.001	0.001	-0.001
startview	1.427	0.999	-0.428
startstopsessionreplayrecording	1.077	0.825	-0.252
logmessage	0.007	0.019	0.012

🧠 Memory Performance

Action Name	Base Consumption Memory (bytes)	Local Consumption Memory (bytes)	𝚫 (bytes)
addglobalcontext	19.58 KiB	18.83 KiB	-766 B
addaction	68.97 KiB	68.36 KiB	-632 B
adderror	83.18 KiB	85.19 KiB	2.00 KiB
addtiming	17.24 KiB	17.05 KiB	-193 B
startview	313.58 KiB	317.81 KiB	4.22 KiB
startstopsessionreplayrecording	11.51 KiB	12.38 KiB	890 B
logmessage	64.11 KiB	67.06 KiB	2.95 KiB