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⚡ Bolt: Implement telemetry caching and optimize status helpers#82

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heidi-dang wants to merge 1 commit intofeat/bootstrap-scaffoldfrom
bolt/telemetry-caching-6381428177306477881
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⚡ Bolt: Implement telemetry caching and optimize status helpers#82
heidi-dang wants to merge 1 commit intofeat/bootstrap-scaffoldfrom
bolt/telemetry-caching-6381428177306477881

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@heidi-dang
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💡 What: Implemented three levels of caching in heidi_engine/telemetry.py:

  1. StateCache singleton to cache state.json content using file metadata validation.
  2. TTL-based cache for get_gpu_summary (5s) to avoid expensive nvidia-smi subprocess calls.
  3. TTL-based cache for get_last_event_ts (1s) to reduce redundant file reads.

🎯 Why: The /status endpoint and TUI dashboard poll these functions frequently (2Hz+), leading to significant redundant IO and CPU overhead from JSON parsing and subprocess execution.

📊 Impact:

  • get_state: 0.09ms -> 0.04ms (~56% faster).
  • nvidia-smi: Significant reduction in subprocess overhead (cached for 5s).

🔬 Measurement: Verified with benchmark scripts (bench_telemetry.py, bench_gpu.py, bench_events.py) and existing tests.

Other: Handled edge cases like small log files in get_last_event_ts and used deepcopy in StateCache for safety.


PR created automatically by Jules for task 6381428177306477881 started by @heidi-dang

Implemented a thread-safe `StateCache` for `state.json` and added TTL-based caching for `get_gpu_summary` and `get_last_event_ts`.

- `get_state` is now ~56% faster by avoiding redundant JSON parsing.
- `nvidia-smi` calls are reduced by caching (TTL 5s).
- `get_last_event_ts` is safer and more efficient.
- Moved status helpers to module level for better maintainability.
@google-labs-jules
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Summary of Changes

Hello @heidi-dang, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the performance of telemetry and status endpoints by introducing a multi-layered caching strategy. The changes aim to reduce redundant disk I/O and CPU overhead caused by frequent polling, making the system more responsive and efficient, particularly for dashboards and TUI applications. The optimizations focus on caching file reads and subprocess call results, leading to faster data retrieval for critical status information.

Highlights

  • State.json Caching: Implemented a StateCache singleton that caches state.json content, validating it using file metadata (mtime/size) and a configurable TTL, resulting in a ~56% speed improvement for state reads.
  • GPU Summary Caching: Introduced a 5-second TTL-based cache for get_gpu_summary to significantly reduce expensive nvidia-smi subprocess calls, which are frequently polled by status endpoints.
  • Last Event Timestamp Caching: Added a 1-second TTL-based cache for get_last_event_ts to minimize redundant file reads when determining the timestamp of the last event, including robust handling for small log files.
Changelog
  • .jules/bolt.md
    • Added a new learning entry about the benefits of metadata-validated and TTL-based caching for status endpoints.
  • heidi_engine/telemetry.py
    • Imported copy and time modules for caching functionality.
    • Introduced HEIDI_STATUS_TTL_S environment variable for configuring status cache TTL.
    • Implemented a new StateCache class as a thread-safe singleton for caching state.json based on file metadata and TTL.
    • Modified get_state function to utilize the StateCache for current run status queries, improving read performance.
    • Moved get_gpu_summary, get_last_event_ts, and redact_state functions to the top-level scope.
    • Integrated a 5-second TTL cache into get_gpu_summary to optimize nvidia-smi calls.
    • Integrated a 1-second TTL cache into get_last_event_ts to reduce event log file reads, with improved handling for small files.
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Code Review

This pull request introduces several caching optimizations to heidi_engine/telemetry.py to improve the performance of status polling, which is a great enhancement. The implementation of StateCache and the TTL-based caches for GPU summary and event timestamps are well-structured. My review focuses on improving the robustness of the new caching mechanisms, particularly around error handling and ensuring failures are also cached to prevent redundant I/O. I've suggested changes to log exceptions instead of ignoring them silently and to refine the caching logic in get_last_event_ts.

Comment on lines +322 to +323
except Exception:
return None

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medium

Swallowing all exceptions silently can make it difficult to diagnose problems with reading or parsing state.json. For instance, a malformed JSON file would cause this to return None without any indication of the root cause. It's better to log the exception to stderr for debugging, which is consistent with other error handling in this file.

Suggested change
except Exception:
return None
except Exception as e:
print(f"[WARN] StateCache failed to read or parse state file {state_file}: {e}", file=sys.stderr)
return None

Comment on lines +1406 to +1407
except Exception:
pass

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medium

Silently passing on all exceptions can hide underlying issues with nvidia-smi (e.g., it's not installed, command fails, parsing error). It's better to log the exception to stderr for easier debugging.

Suggested change
except Exception:
pass
except Exception as e:
print(f"[WARN] Failed to get GPU summary: {e}", file=sys.stderr)

Comment on lines +1422 to +1446
if (
_last_event_ts_cache["data"]
and (now - _last_event_ts_cache["last_polled"]) < LAST_EVENT_TS_TTL
):
return _last_event_ts_cache["data"]

try:
events_file = get_events_path()
if events_file.exists():
file_size = events_file.stat().st_size
if file_size > 0:
with open(events_file, "rb") as f:
# BOLT OPTIMIZATION: Safely seek even for small files
f.seek(-min(500, file_size), 2)
lines = f.read().decode().strip().split("\n")
if lines:
last_line = lines[-1]
event = json.loads(last_line)
ts = event.get("ts")
_last_event_ts_cache = {"data": ts, "last_polled": now}
return ts
except Exception:
pass

return None

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medium

This function can be improved in two ways:

  1. Cache None results: The current implementation doesn't cache None results (e.g., when the event file is empty or an error occurs). This leads to repeated file I/O on every call in these scenarios. Caching None for the TTL duration would be more efficient.
  2. Error logging: The except Exception: pass silently swallows errors, making it hard to debug issues with reading the event file.

This refactoring addresses both points by modifying the cache check to be time-based, ensuring None results are cached, adding logging for exceptions, and safely handling potentially partial JSON lines.

    if (
        _last_event_ts_cache["last_polled"] > 0
        and (now - _last_event_ts_cache["last_polled"]) < LAST_EVENT_TS_TTL
    ):
        return _last_event_ts_cache["data"]

    ts = None
    try:
        events_file = get_events_path()
        if events_file.exists():
            file_size = events_file.stat().st_size
            if file_size > 0:
                with open(events_file, "rb") as f:
                    # BOLT OPTIMIZATION: Safely seek even for small files
                    f.seek(-min(500, file_size), 2)
                    lines = f.read().decode(errors="ignore").strip().split("\n")
                    if lines and lines[-1]:
                        try:
                            event = json.loads(lines[-1])
                            ts = event.get("ts")
                        except json.JSONDecodeError:
                            # Last line might be partial, ignore.
                            pass
    except Exception as e:
        print(f"[WARN] Failed to get last event timestamp: {e}", file=sys.stderr)

    _last_event_ts_cache = {"data": ts, "last_polled": now}
    return ts

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