Statistics

Eneru writes UPS history to SQLite. The TUI graphs, event panel, notification retry queue, and offline troubleshooting all use the same per-UPS database files.

Statistics are always enabled. If the database cannot be opened or written, Eneru logs the problem and keeps monitoring.

Storage path

statistics:
  db_directory: "/var/lib/eneru"
  retention:
    raw_hours: 24
    agg_5min_days: 30
    agg_hourly_days: 1825

The package creates /var/lib/eneru. PyPI installs create it on first daemon start if permissions allow.

Each UPS gets its own .db file named from the sanitized UPS label.

Write path

UPS poll loop
    |
    v
append sample to in-memory buffer
    |
    v
StatsWriter flushes every ~10 seconds
    |
    v
SQLite samples table
    |
    v
5-minute and hourly aggregates

Polls do not wait on SQLite writes. The writer batches rows in the background. Event rows are inserted directly, but failures are isolated from the safety-critical monitor path.

Stats write timeline

These intervals come from StatsWriter defaults in src/eneru/stats.py: flush_interval=10.0 and maintenance_interval=300.0.

Time	Action	Result
Every poll	Monitor appends sample to memory	No SQLite work runs on the hot path
About every 10s	Writer flushes buffered samples	One batched SQLite transaction persists recent samples
Every 300s	Writer aggregates raw rows	agg_5min receives new buckets
Every 300s	Writer rolls 5-minute buckets	agg_hourly receives hourly buckets
Every 300s	Retention runs	Old raw and aggregate rows are purged by tier
Any SQLite failure	Error is logged and rate-limited	Monitoring continues without stats persistence

Tables

Table	Purpose
samples	Raw poll samples, typically 1 Hz
agg_5min	Five-minute aggregate buckets
agg_hourly	Hourly aggregate buckets
events	Power, health, lifecycle, slow-response diagnostics, remote-health transition, and shutdown events. Each row has an id (INTEGER PRIMARY KEY AUTOINCREMENT, schema v5) that the API uses to target individual events for deletion; the id is never reused, so deletion is always safe
notifications	Persistent notification queue and delivery history
meta	Schema version and lifecycle metadata

The main sample metrics include status, battery charge, runtime, load, input/output voltage, battery voltage, temperature, frequency, depletion rate, time on battery, and connection state.

Retention

Tier	Default retention	Use
Raw samples	24 hours	Detailed incident review
Five-minute aggregates	30 days	Recent trends
Hourly aggregates	5 years	Long-term battery and load history

Raw rows are deleted after they have been aggregated. Aggregates have their own retention windows.

Disk usage

At a 1-second poll interval, expect roughly 15 to 20 MB per UPS at the default retention settings, plus small growth from events and notification rows.

For SD-card systems, the write pattern is a small transaction about every 10 seconds per UPS. That is usually less write pressure than normal system logging, but you can move the database to better storage:

statistics:
  db_directory: "/mnt/ssd/eneru-stats"

Make sure the daemon user can write there.

Inspect data

List databases:

sudo ls -lh /var/lib/eneru/

Show tables:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db ".tables"

Recent samples:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db <<'SQL'
.headers on
.mode column
SELECT datetime(ts, 'unixepoch') AS time,
       status,
       battery_charge,
       battery_runtime,
       ups_load,
       input_voltage
FROM samples
ORDER BY ts DESC
LIMIT 20;
SQL

Recent events:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db \
  "SELECT datetime(ts, 'unixepoch'), event_type, detail FROM events ORDER BY ts DESC LIMIT 20;"

Slow NUT and remote SSH probes are stored as diagnostics events (SLOW_NUT_RESPONSE and REMOTE_SSH_SLOW_RESPONSE). They show in the TUI and /api/v1/events when event verbosity includes Diagnostics (-v / verbosity=1).

Muted events:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db \
  "SELECT event_type, COUNT(*) FROM events WHERE notification_sent = 0 GROUP BY event_type;"

Pending notifications:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db \
  "SELECT id, attempts, next_attempt_at, title FROM notifications WHERE status='pending';"

TUI graphs

eneru monitor reads the stats database read-only. Graphs select the smallest table that covers the requested time range:

Window	Table	Resolution
Up to 24 hours	samples	Per poll
Up to 30 days	agg_5min	Five-minute buckets
More than 30 days	agg_hourly	Hourly buckets

See Monitor and graphs for TUI usage.

Backup

SQLite supports online backup without stopping Eneru:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db \
  ".backup '/srv/backups/UPS-192-168-1-100.db'"

Schema migrations

Eneru stores the schema version in meta.schema_version. New releases migrate existing databases with additive ALTER TABLE statements and preserve old rows. When a column cannot be added in place, the table is rebuilt inside the same transaction. Schema v5 does this for events.id INTEGER PRIMARY KEY AUTOINCREMENT, which SQLite cannot ALTER ADD; existing rows keep their identity as id = old rowid, so the migration is still atomic and replay-safe.

Check the version:

sqlite3 /var/lib/eneru/UPS-192-168-1-100.db \
  "SELECT key, value FROM meta WHERE key='schema_version';"

Migrations are designed to be replay-safe. If a daemon crashes mid-migration, the next start retries before bumping the schema version.

Failure behavior

Stats failures do not stop monitoring or shutdown. You may see logs like:

stats store open failed at /var/lib/eneru/UPS.db: ...
stats: flush failed: disk I/O error

Fix the storage problem, then restart Eneru so it can reopen the database.