Node.js › Caching

How would you implement a write-behind (write-back) caching strategy, and what durability risk does it introduce?

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Answer

Write-behind caching writes changes to the cache immediately and defers the actual write to the durable database to a later batched operation, improving write throughput significantly, but introducing a durability risk: if the process crashes before the deferred write happens, that data is permanently lost, so this pattern is only appropriate when losing a small, recent window of writes is genuinely acceptable.

const writeBuffer = new Map();

function recordPageView(pageId) {
  writeBuffer.set(pageId, (writeBuffer.get(pageId) || 0) + 1);
}

setInterval(async () => {
  for (const [pageId, count] of writeBuffer) {
    await db.pageViews.increment(pageId, count);
  }
  writeBuffer.clear();
}, 30000);

Real-world example An analytics system tracking page-view counts buffers increments in memory and flushes them to the database every 30 seconds, accepting a small window of possible data loss on crash since exact real-time counts aren't business-critical.

Common follow-ups: What data would be completely inappropriate to cache using a write-behind strategy given this durability risk?;How would you reduce the durability risk without giving up the throughput benefit entirely, such as more frequent flushing?

Databases & ORMs (MongoDB/Mongoose SQL/Sequelize);Performance Optimization & Profiling