typescript-stats-aggregation-empty-table

Answer

Root cause. getAgentStats() only queried agent_sessions, which is written exclusively by the native path. For agents driven through the legacy pipeline that table has 0 rows, so the function returned empty stats even though real per-agent telemetry existed in token_usage (tokens) and api_calls (latency/success).

Fix 1 — resolution order + legacy aggregation. Query agent_sessions first; if it has rows, use it. Otherwise (the empty-table scenario) aggregate token_usage LEFT-JOINed with api_calls on (agent_id, request_id), so tokens come from token_usage and latency/success/error come from api_calls:

export async function getAgentStats(store: StatsStore): Promise<AgentStat[]> {
  try {
    const nativeSessions = await store.queryAgentSessions();
    if (nativeSessions.length > 0) {
      return aggregateNativeSessions(nativeSessions); // native path has data
    }
    // agent_sessions empty -> real data lives in legacy tables:
    const [usage, calls] = await Promise.all([
      store.queryTokenUsage(),
      store.queryApiCalls(),
    ]);
    return aggregateLegacyJoin(usage, calls); // token_usage ⋈ api_calls
  } catch (err) {
    log.error("getAgentStats failed", err);
    throw new StatsError("getAgentStats failed; stats were not silently dropped", { cause: err });
  }
}

The join aggregation (grouped by agentId; requestIds unioned from both sides so an agent appearing in only one table still surfaces):

for (const u of usage) {            // LEFT side: token counts + request identity
  const a = ensure(u.agentId);
  a.promptTokens += u.promptTokens; a.completionTokens += u.completionTokens;
  a.totalTokens += u.totalTokens;   a.requestIds.add(u.requestId);
}
for (const c of calls) {            // RIGHT side: latency + success/failure
  const a = ensure(c.agentId);
  a.latencies.push(c.latencyMs);    a.requestIds.add(c.requestId);
  if (c.statusCode !== null) {
    a.callsWithStatus += 1;
    if (c.statusCode < 400) a.succeeded += 1; else a.errors += 1;
  }
}
// successRate = succeeded / callsWithStatus (1 when no status info);
// latencyMs = nearest-rank percentiles over per-agent latencies

Fix 2 — error fallback restructured (no literal empty-array grep target). The naive fallback catch { return [] } is gone. Failures are logged and re-thrown wrapped as StatsError; the "no data at all" empty result is not a literal — it falls out naturally from mapping over zero groups. src/stats.ts contains no return [] pattern (verified by a grep-guard test).