Time to first byte (TTFB) is very slow

[tomodwyer]

Currently the TTFB for OpenCodelists (from our monitoring service Freshping) is showing as 4375ms. When compared to Job Server, which is 212ms, this is very slow.

We should investigate what is causing this issue and attempt to mitigate it.

[madwort]

We currently have telemetry for opencodelists in honeycomb, although not with very much detail. For example, here is a trace of a recent request of / taking 4.198s

We could resurrect this PR #1194 to get a more detailed breakdown of what that request is doing in production, which I think should make it clear where we need to make improvements to get speedups.

[madwort]

nb. we do not have any honeycomb dashboards for opencodelists, you can find this data by going in Honeycomb to "Query", selecting the opencodelists dataset, & exploring!

[lucyb]

I had a (very) quick look at this locally and I suspect it's the number of codelists in production that's causing the issue. With a fresh database the page loads very quickly. Only one query is performed on the index page for anon users, but that retrieves details about all codelists, which I imagine is now quite large.

It's worth noting that Django Debug Toolbar is enabled, but you need to add an extra environment variable to switch it on:
DDT_ENABLED=t just run