masaori335 opened a new pull request, #13328:
URL: https://github.com/apache/trafficserver/pull/13328
# Motivation
Cold-start cache initialization rebuilds each stripe's in-memory directory
from disk on every
restart — multi-minute on large caches.
# Approach
Host the directory (`raw_dir`) in POSIX shared memory so the next process
start attaches the
existing segment in milliseconds instead of rebuilding it. Recovery is
binary and fail-safe:
anything untrustworthy (crash, reboot, ABI/schema mismatch, failed
validation, bad disk) falls
back to the existing disk-rebuild path, and reads still validate `Doc` magic
+ key so a stale
entry is a miss, never served corruption.
# New configs & traffic_ctl commands
Opt-in behind `proxy.config.cache.shm.enabled` (default `0`, a functional
no-op). Also adds
`proxy.config.cache.shm.{name_prefix,use_hugepages,purge_stale_on_start}`
and a
`traffic_ctl cache shm status|clear` command.
# Details
Design, recovery model, configuration, and platform notes are in
`doc/developer-guide/cache-architecture/shm-fast-restart.en.rst` (added in
this PR) and the
`proxy.config.cache.shm.*` entries in `records.yaml`.
# Testing
- Unit: `test_CacheShm` (ABI hash, storage signature, control round-trip,
name length, prefix
normalization, process liveness).
- AuTest: 7 `cache_shm_*` suites — fast restart, unclean shutdown,
schema/storage mismatch,
bad-disk drop + orphan reclaim, concurrent-attach refusal,
purge-on-disable.
# Caveats
- No automated test yet exercises the `_shm_directory_is_valid()` rejection
branches or the
bad-disk / flush-failure `invalidate_stripe_directory()` paths (planned
follow-up).
- macOS concurrent-attach is best-effort: the `flock` guard is authoritative
on Linux but a
no-op on macOS POSIX shm, where it falls back to an owner-pid liveness
check.
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