1.0.0-52 throttled the percent/bb_phase writes but missed:
- `_is_cancelled` ran a DB query on EVERY stderr line (sub-second
cadence × 4 concurrent burn-ins = ~10+ DB connection opens/s)
- `_append_stage_log` ran every 20 output_lines (~once per second)
doing a quadratic `log_text || ?` concat that gets multi-MB
rewrites as the log grows
- `_recalculate_progress` + `_push_update` also fired per gated tick
Cumulative load kept the asyncssh drain coroutine too busy to
consume the SSH channel buffer; SSH window stalled; sshd stopped
reading the pipe; badblocks blocked on pipe_write with state=S
wchan=pipe_write. /sys/block sectors_written delta confirmed
0 disk I/O across all running drives despite 23h elapsed.
Fix:
1. Single throttle gate (BB_DB_MIN_SECONDS=5s) covers EVERY DB
touch in the drain — cancel check, percent/phase/bb_count
updates, throughput sample, log flush, recalc, SSE push.
Phase transitions still bypass the throttle (rare + important).
2. Exclude "XX% done" lines from the log entirely. They were the
dominant volume; meaningful content (pattern headers, errors,
bad-block numbers) still gets logged via the throttled flush.
3. log_text concat still quadratic but the volume reduction makes
it tractable — buffer to pending_log_chunks, flush on the gate.
Net effect: ~99% reduction in drain-loop DB load. asyncssh drain
keeps up; pipe drains; badblocks writes; disk goes brr.
149f2901b7