The non-inline rename_data commit path made the tmp xl.meta durable and then
fdatasynced the shard files in two sequential awaits, each its own blocking
round-trip. The two operations touch disjoint paths (the tmp xl.meta under the
tmp bucket vs the shard data dir) and have no ordering constraint between them:
both only need to be durable before the commit renames that follow.
Run them concurrently with tokio::join!, dropping a blocking round-trip from
the PUT commit critical path (backlog#922 step 2). The commit ordering is
unchanged — both futures complete before any rename, and a failure in either
aborts before the rename exactly as the sequential version did (tmp-meta error
is still surfaced first). Payload and metadata durability semantics are
identical under strict and relaxed tiers.
Validated by the rename_data crash-consistency harness (backlog#935): a crash
at any pre-commit point still reopens as old-or-new, never mixed. Existing
rename_data / durability-tier / disk::os tests are unchanged and pass.
Refs: rustfs/backlog#922 (HP-1 step 2), rustfs/backlog#936
Co-authored-by: heihutu <[email protected]>
