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fix(db): cap pg pool + stop retrying pool saturation (Supabase EMAXCONNSESSION) #284

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fix(db): cap pg pool + stop retrying pool saturation (Supabase EMAXCONNSESSION) #284

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42 changes: 33 additions & 9 deletions src/server/db.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,22 @@ const INITIAL_RETRY_DELAY_MS = 500;

// Check if error is a connection error that should be retried
const isConnectionError = (error: unknown): boolean => {
// Pool saturation must NEVER be retried. Retrying hammers an already
// saturated pool and amplifies the outage. This covers the Supabase
// Supavisor session-mode limit (EMAXCONNSESSION / "max clients reached")
// and the node-postgres pool acquire timeout ("timeout exceeded when
// trying to connect"). Fail fast so the request errors instead of looping.
if (error instanceof Error) {
const m = error.message.toLowerCase();
if (
m.includes("max clients reached") ||
m.includes("pool_size") ||
m.includes("emaxconnsession") ||
m.includes("timeout exceeded when trying to connect")
) {
return false;
}
}
if (error instanceof Prisma.PrismaClientKnownRequestError) {
// P1001: Can't reach database server
// P1008: Operations timed out
Expand Down Expand Up @@ -55,14 +71,9 @@ const withRetry = async <T>(
}

await new Promise((resolve) => setTimeout(resolve, delay));

// Try to reconnect before retrying
try {
await prismaClient.$connect();
} catch {
// Ignore connection errors here, let the retry handle it
}


// Do NOT call $connect() here: the pg driver-adapter pool reconnects
// lazily, and forcing a connect against a saturated pool only adds load.
return withRetry(operation, retries - 1);
}
throw error;
Expand Down Expand Up @@ -104,7 +115,20 @@ const createPrismaClient = () => {
// Prisma 7 requires a driver adapter (or Accelerate) instead of a schema/url
// connection. The pg adapter connects via the pooled DATABASE_URL; migrations
// use the direct connection configured in prisma.config.ts.
const adapter = new PrismaPg({ connectionString: env.DATABASE_URL });
// Cap the node-postgres pool per serverless instance. Without `max`,
// node-postgres defaults to 10 connections/instance — a few warm Vercel
// instances overrun Supabase's session-mode pool (15 client slots) and
// every query fails with EMAXCONNSESSION. A small max keeps connections
// well under the pooler limit and preserves transaction-mode multiplexing;
// concurrent intra-request queries queue rather than deadlock (they each
// release per statement). Finite timeouts make a saturated pool fail fast
// instead of hanging on the pg default connectionTimeoutMillis: 0 (infinite).
const adapter = new PrismaPg({
connectionString: env.DATABASE_URL,
max: 2,
idleTimeoutMillis: 10_000,
connectionTimeoutMillis: 10_000,
});

const client = new PrismaClient({
adapter,
Expand Down
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