Files
scylladb/utils
Tomasz Grabiec f7c001deff Merge 'key: clustering_bounds_comparator: avoid thread_local initialization guard overhead' from Avi Kivity
I noticed clustering_bounds_comparator was running an unnecessary
thread_local initialization guard. This series switches the variable
to constinit initialization, removing the guard.

Performance measurements (perf-simple-query) show an unimpressive
20 instruction per op reduction. However, each instruction counts!

Before:

```
throughput:
	mean=   203642.54 standard-deviation=1102.99
	median= 204328.69 median-absolute-deviation=955.56
	maximum=204624.13 minimum=202222.19
instructions_per_op:
	mean=   42097.59 standard-deviation=40.07
	median= 42111.83 median-absolute-deviation=30.65
	maximum=42139.88 minimum=42044.91
cpu_cycles_per_op:
	mean=   22664.81 standard-deviation=131.28
	median= 22581.10 median-absolute-deviation=111.57
	maximum=22832.30 minimum=22553.24
```

After:

```
throughput:
	mean=   204397.73 standard-deviation=2277.71
	median= 204942.95 median-absolute-deviation=2191.54
	maximum=207588.30 minimum=202162.80
instructions_per_op:
	mean=   42087.21 standard-deviation=27.30
	median= 42092.75 median-absolute-deviation=20.33
	maximum=42108.33 minimum=42041.51
cpu_cycles_per_op:
	mean=   22589.79 standard-deviation=219.24
	median= 22544.82 median-absolute-deviation=191.98
	maximum=22835.11 minimum=22303.52
```

(Very) minor performance improvement, no backport suggestd.

Closes scylladb/scylladb#25259

* github.com:scylladb/scylladb:
  keys: clustering_bounds_comparator: make thread_local _empty_prefix constinit
  keys: make empty creation clustering_key_prefix constexpr
  managed_bytes: make empty managed_bytes constexpr friendly
  keys: clustering_bounds_comparator: make _empty_prefix a prefix
2025-08-11 13:20:38 +02:00
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