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Here's what a CPU profile from a variant of admission-control/elastic-cdc (added in #89656) looks like. In this version we set up a few rangefeeds against 8vCPU nodes running TPC-C with 1000-warehouses, running with just initial_scan = 'only'.

The profile tells us that a lot of CPU hit is due to the parallel workers receiving events off of the KV feed. The tiny purple segment on the right is the scan portion down in KV. When we tried integrating just that bit with the elastic CPU limiter (a now lost revision of #89709), we were still ineffective in bounding effects on scheduling latencies since so much CPU is used up elsewhere. We ought to integrate this work with the elastic CPU limiter.

Epic CRDB-24463