TJ Downes d592af6e19 fix(rrdtool): replace rrdtool.info() with self-tracked timestamp to eliminate allocation storm ...

Problem
-------
update_packet_metrics() called rrdtool.info() (cached for 5 s) to get the
RRD's last_update timestamp.  rrdtool.info() returns a massive Python dict:
17 data sources × 5 RRAs × ~8 fields each = ~700+ dict entries per call.
tracemalloc showed +10696 new allocations / +251 KB at this exact line,
flagged as "Investigate" in the memory diagnostics dashboard.

The rrdtool.info() approach was also unnecessarily complex: it required a
5-second secondary cache, a _pending_rrd_update buffer, and two extra
instance attributes — all to answer one question ("did we already write
this period?") that we can answer ourselves with a single integer.

Fix
---
Replace _last_rrd_info_cache / _last_rrd_info_time / _pending_rrd_update
with a single self._last_rrd_update: int = 0 that stores the timestamp of
the last successful rrdtool.update() call.  The throttle check becomes:

    if timestamp <= self._last_rrd_update:
        return

On success: self._last_rrd_update = timestamp

Zero dict allocations per call.  The only downside vs rrdtool.info() is
that _last_rrd_update resets to 0 on process restart, meaning the first
packet after a restart always triggers a write — correct behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2026-04-21 20:50:27 -07:00

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