LaserStream Historical Replay: Backfill Missing Data
Recover from disconnections and backfill missing Solana blockchain data with LaserStream’s historical replay feature. Never miss a transaction again.
Never miss a beat: LaserStream’s Historical Replay ensures you can recover from disconnections and backfill missing data from the last 24 hours of blockchain activity.
Historical Replay is LaserStream’s feature that lets you replay recent blockchain data by setting a fromSlot starting point. This is useful for handling disconnections and ensuring data continuity in real-time apps.
You can replay up to ~24 hours (~216,000 slots) of history, regardless of which commitment level you subscribe with. Pass a fromSlot within that window and LaserStream streams forward from there to the present.Older replays return finalized data. LaserStream keeps roughly the last ~20 minutes of slots in memory; anything older is served from a historical store that holds finalized blocks only. So when you replay a fromSlot older than ~20 minutes, the data reflects the finalized chain — you won’t see forked or dropped slots or intra-slot account updates in that range, even on a processed or confirmed subscription. Slots within the last ~20 minutes carry true commitment semantics, including forks and intra-slot account updates.
Limited Time Window: Historical replay only covers the last ~24 hours. You cannot replay data from arbitrary points in the past.
Handle Disconnections
Recover data lost during brief disconnections (up to 24 hours)
Bootstrap Applications
Start applications with recent context from the last 24 hours
Get started with LaserStream from your Helius Dashboard. Mainnet requires a Business or Professional plan; Devnet is available on Developer and above. See Plans & Pricing for details.
gRPC
import { subscribe, CommitmentLevel, LaserstreamConfig, SubscribeRequest } from 'helius-laserstream';// Pick a slot within the last ~216,000 slots (≈24 h). For a real start// value, call `getSlot` first and subtract however far back you want to replay.// Note: replays older than ~20 min return finalized data even at processed/confirmed;// slots within the last ~20 min carry true commitment semantics.const fromSlot = 419_800_000;const subscriptionRequest: SubscribeRequest = { transactions: { "token-filter": { // user-defined label for this filter accountInclude: ['TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA'], vote: false, failed: false } }, commitment: CommitmentLevel.CONFIRMED, accounts: {}, slots: {}, blocks: {}, blocksMeta: {}, entry: {}, accountsDataSlice: [], fromSlot, // u64 slot number; must fall inside the replay window};const config: LaserstreamConfig = { apiKey: 'YOUR_API_KEY', endpoint: 'https://laserstream-mainnet-ewr.helius-rpc.com', // Choose your closest region};await subscribe(config, subscriptionRequest, async (data) => { console.log('Received data:', data); }, async (error) => { console.error('Error:', error); });
The slot number to start replaying from, as a u64. Must be within the replay window (last ~216,000 slots / ~24 hours from the current slot), at any commitment level.Example: currentSlot - 1000Important: If you pass a slot older than the window, LaserStream rejects the request with Operation was attempted past the valid range.
When your application reconnects after a short disconnection (under 24 hours), you can use Historical Replay to ensure no data is missed. getCurrentSlot calls the Helius RPC; lastProcessedSlot is kept in memory below — persist it however suits your app (Redis, Postgres, a file, etc.).
async function getCurrentSlot(): Promise<number> { const r = await fetch(`https://mainnet.helius-rpc.com/?api-key=${process.env.HELIUS_API_KEY}`, { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ jsonrpc: '2.0', id: 1, method: 'getSlot', params: [{ commitment: 'confirmed' }] }), }); const { result } = await r.json(); return result as number;}// Load the last slot you processed from wherever you store it.let lastProcessedSlot = Number(process.env.LAST_PROCESSED_SLOT ?? 0);// Check if it's still within the replay windowconst currentSlot = await getCurrentSlot();const maxReplaySlot = currentSlot - 216_000;if (lastProcessedSlot < maxReplaySlot) { console.warn('Disconnection too long, some data may be lost'); lastProcessedSlot = maxReplaySlot;}const subscriptionRequest: SubscribeRequest = { // ... your subscription config fromSlot: lastProcessedSlot, // pass as number, not string};await subscribe(config, subscriptionRequest, async (data) => { // your handler here if (data.transaction?.slot) { lastProcessedSlot = Number(data.transaction.slot); // persist `lastProcessedSlot` here so the next reconnect picks up } });
Bootstrap with Recent Context
Start your application with recent context from the last few minutes:
// Get a slot from 10 minutes ago (within the 24-hour window)const currentSlot = await getCurrentSlot();const startSlot = currentSlot - 1500; // ~10 minutes agoconst subscriptionRequest: SubscribeRequest = { // ... your subscription config fromSlot: startSlot, // u64 number};
Testing with Recent Data
Use recent historical data for testing (limited to last 24 hours):
// Test with data from the last 5 minutesconst currentSlot = await getCurrentSlot();const testStartSlot = currentSlot - 750; // ~5 minutes agoconst testEndSlot = currentSlot - 150; // ~1 minute agoconst subscriptionRequest: SubscribeRequest = { // ... your subscription config fromSlot: testStartSlot, // u64 number};// Stop processing when reaching the test end slotconst stream = await subscribe(config, subscriptionRequest, async (data) => { const slot = Number(data.transaction?.slot ?? data.account?.slot ?? 0); if (slot >= testEndSlot) { stream.cancel(); return; } // your test handler here });
