Third layer of the multi-session concurrency story. After Layers
1+2 (67cd8f2 — shared DATA-INIT hash + recCount cache
invalidation), the residual flake had this exact failure mode:
goroutine A: OPEN -> Append (recCount→1, hdr=1) -> ...
goroutine B: OPEN -> Append (refresh→1, bump to 2, hdr=2) -> ...
goroutine B: Close -> flushRecord -> updateHeader (writes 2)
goroutine A: Close -> flushRecord -> updateHeader (writes 1) ← clobbers!
A's updateHeader unconditionally wrote a.recCount back to disk,
even when the disk header had been bumped by B's append-intent-
locked Append in between. Subsequent peer SELECTs then read
hdr=1 and iterated only as far as slot 1, missing B's row that
was physically present at slot 2.
Fix: in shared mode, updateHeader re-reads the disk header first
and writes back max(disk.RecCount, a.recCount). Correct under
the existing append-intent-lock invariant (the disk count is
monotonically nondecreasing across all peers); cheap (~1 stat-
sized read per close, never on the hot append path).
EXCLUSIVE mode keeps the old unconditional write — no peer can
have bumped the header, so the read+max is pure overhead with
no upside.
Measured impact (3-worker concurrent insert+select+commit × 20 runs):
pre-67cd8f2: ~60% pass, occasional Go panic
after 67cd8f2: 80% pass, no panics
after THIS: 80% pass, no panics (3-worker stable)
after THIS: 50% pass (5-worker — higher load uncovers
additional races at the multi-area mmap layer)
The remaining 5-worker flake points at a deeper issue: peer
DBFArea instances on the same file each hold their own mmap,
and the mmap snapshot taken at Open time doesn't track grow-by-
peer events between mmap-time and the next read. loadRecord
falls back to ReadAt when offset > len(mmap), so reads
themselves work — but the per-area appendBuf interaction with
peer-bumped header values needs more thought. Tracked as a
proper follow-up; the architectural shape is "every shared
DBFArea registers in a per-path mmap-gen registry that
broadcasts grow-events".
All six release gates green:
go test ./... ✓
FiveSql2 SQL:1999 43/43 ✓
Harbour compat 56/56 ✓
std.ch 17/17 ✓
FRB 7/7 ✓
pgserver integration 6/6 ✓
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
CharlesKWON
4fd14f63ef