Cache Daily Stock Candles Aggressively — They Barely Change

When building a stock technical analysis dashboard, I initially cached daily candle data for just 5 minutes. That’s way too conservative — daily candles only change once per day after market close.

The Insight

Daily OHLCV (Open/High/Low/Close/Volume) candle data is essentially immutable for historical days. Even the current day’s candle only updates during market hours. For IDX (Indonesia Stock Exchange), that’s 09:00–15:30 WIB.

Two-Layer Caching Strategy

Layer 1: Raw data cache (1 hour TTL) Cache the fetched daily history from the data provider (Yahoo Finance). Even during market hours, 1-hour staleness is fine for daily timeframe analysis.

Layer 2: Computed TA summary cache (30 min TTL, per user) Technical analysis computations (RSI, MACD, Bollinger, confluence scores) are expensive when run across an entire watchlist. Cache the computed results per user and invalidate on watchlist changes (add/remove stock).

// Invalidate TA cache when watchlist changes
export function invalidateTACache(userId: string) {
  taSummaryCache.delete(userId);
}

The takeaway: Match your cache TTL to how often the underlying data actually changes, not to how often users might request it. For daily candles: hours, not minutes.