---
plan: 04-01
status: complete
completed: "2026-03-19"
commits:
  - fd4a0e4: "feat(streaming): increase WS channel capacity from 1000 to 50000 (PARA-04)"
  - c247b76: "feat(streaming): parallel fill_from_rest with JoinSet + Semaphore(4) (PARA-01, PARA-02, PARA-03)"
---

# Summary: 04-01 Parallel fill_from_rest

## Changes

### Task 1: WS channel capacity (PARA-04)

- Changed both `mpsc::channel::<AggTrade>(1000)` to `mpsc::channel::<AggTrade>(50_000)` in `start_ws()` and `symbol_task()` fallback path
- Updated doc comment to reflect new capacity

### Task 2: Parallel fill with JoinSet + Semaphore(4) (PARA-01, PARA-02)

- Replaced sequential `for symbol in &self.config.symbols` loop with `JoinSet` + `Semaphore::new(4)`
- Each symbol's fill runs as a spawned tokio task, acquiring a semaphore permit before REST fetch
- Shared state extracted before spawning: `initial_checkpoints` (taken via `std::mem::take`), `bar_buffer` (via `clone_ref()`), `metrics` (via `Arc::clone`), `rate_limiter` (via `Clone`)
- Each task returns `(symbol, processors, bars_count, trades_count)` for aggregation
- Results collected via `join_set.join_next()` with error handling for both processing errors and panics
- Rate limiter ceiling set to 4800 before fill, 3000 after (PARA-03 integration)

### Task 3: Total fill duration logging (PARA-02 measurement)

- Added `Instant::now()` at fill start and `total_duration_ms` in completion log
- Provides production measurement point for verifying <90s target

## Verification

- `cargo check -p opendeviationbar-streaming` passes
- All grep-verifiable acceptance criteria confirmed:
  - 2 occurrences of `mpsc::channel::<AggTrade>(50_000)`, 0 of `(1000)`
  - JoinSet, Semaphore::new(4), set_ceiling(4800), set_ceiling(3000) all present
  - `total_duration_ms` in tracing output
