PostHog's Session Replay feature degrades Google services performance

[katcinskiy]

I noticed that Google Street View and Google Maps are lagging when PostHog's session replay is active. Every time a screenshot is captured, there's a noticeable drop in frame rate that decreases the overall smoothness of Street View navigation.

I've observed that the smaller the config.sessionReplayConfig.debouncerDelay value, the less smooth the panorama becomes, so probably this is the root cause.

Here's my configuration:

let config = PostHogConfig(apiKey: "", host: "https://eu.i.posthog.com")

config.captureScreenViews = false
config.captureApplicationLifecycleEvents = true
config.sessionReplay = true
config.sessionReplayConfig.screenshotMode = true
config.sessionReplayConfig.captureNetworkTelemetry = true
config.sessionReplayConfig.maskAllImages = false
config.sessionReplayConfig.maskAllTextInputs = false
config.sessionReplayConfig.debouncerDelay = 1.0
PostHogSDK.shared.setup(config)

I didn't experience it with SmartLook session replay.

[ioannisj]

Hey @katcinskiy, thank you for flagging this. I'll take a closer look and try and identify the bottleneck in the snapshot rendering pipeline. In the meantime, if you can attach a sample project with a screen that includes a Google Maps showcasing the lagging issue it would really speed things up for me 🙏

[katcinskiy]

@ioannisj sorry for the delay. Sure I will provide you example with panorama view. Please replace <gms_key> and <posthog_api_key>

google-streetview-test.zip

Here is the screencasts WITH post hog and WITHOUT, in PostHog version you can see some glitches:

with_posthog.mov

without_posthog.mov

[ioannisj]

Thanx @katcinskiy! I'll have a closer look and revert soon.

[ioannisj]

Quick update on this — I tested it on my device and didn’t notice any major frame drops with or without session replay enabled (though this could vary between high and low-end devices). That said, I did spot some medium hitches in Instruments during screenshot capture, so I’m digging into the snapshot rendering pipeline to see where we can improve performance.

There’s an alternative approach using layer rendering, which should be faster. However, since Google Maps uses a custom rendering layer, it ends up appearing gray in the recordings — so it’s a bit of a trade-off, and I'm guessing this change will have a broader impact on users.

I’ll keep experimenting and continue the quest — will keep you posted! 🙏

[finder39]

@ioannisj I am also having a similar issue where every second (when a snapshot is taken) it takes a ton of processor and makes our app stutter, most noticeable during scrolling. I believe this is from the same root cause. Our app is a SwiftUI based app that is using session replay. I'll attach a stack trace which hopefully helps

[ioannisj]

@finder39 thanx for the trace. What device was this running on?

[finder39]

@ioannisj this is on an iPhone 16 Pro running 18.4.1

[ioannisj]

@finder39 and I assume on latest version? I'll push some exploratory changes on Monday probably, would you be okay guys if I ping you then so you can test them out on the same project?

[finder39]

@ioannisj we are running the latest PostHog version, yes. I'd be happy to test out a version if you sent it off to me.