Re: Add progressive backoff to XactLockTableWait functions

Although it’s clear that replacing tight 1 ms polling loops will reduce CPU usage, I'm curious about the hard numbers. To that end, I ran a 60 s logical-replication slot–creation workload on a standby using three different XactLockTableWait() variants—on an 8-core, 16 GB AMD system—and collected both profiling traces and hardware-counter metrics. 

1. Hardware‐counter results

• CPU cycles drop by 58% moving from 1 ms to exp. backoff, and another 25% to the 1 s threshold variant.
• Cache‐misses and context‐switches see similarly large reductions.
• IPC remains around 0.45, dipping slightly under longer sleeps.