Add better pooling controls

server/db/pg/poolConfig.ts

@@ -0,0 +1,63 @@
+import { Pool, PoolConfig } from "pg";
+import logger from "@server/logger";
+
+export function createPoolConfig(
+    connectionString: string,
+    maxConnections: number,
+    idleTimeoutMs: number,
+    connectionTimeoutMs: number
+): PoolConfig {
+    return {
+        connectionString,
+        max: maxConnections,
+        idleTimeoutMillis: idleTimeoutMs,
+        connectionTimeoutMillis: connectionTimeoutMs,
+        // TCP keepalive to prevent silent connection drops by NAT gateways,
+        // load balancers, and other intermediate network devices (e.g. AWS
+        // NAT Gateway drops idle TCP connections after ~350s)
+        keepAlive: true,
+        keepAliveInitialDelayMillis: 10000, // send first keepalive after 10s of idle
+        // Allow connections to be released and recreated more aggressively
+        // to avoid stale connections building up
+        allowExitOnIdle: false
+    };
+}
+
+export function attachPoolErrorHandlers(pool: Pool, label: string): void {
+    pool.on("error", (err) => {
+        // This catches errors on idle clients in the pool. Without this
+        // handler an unexpected disconnect would crash the process.
+        logger.error(
+            `Unexpected error on idle ${label} database client: ${err.message}`
+        );
+    });
+
+    pool.on("connect", (client) => {
+        // Set a statement timeout on every new connection so a single slow
+        // query can't block the pool forever
+        client.query("SET statement_timeout = '30s'").catch((err: Error) => {
+            logger.warn(
+                `Failed to set statement_timeout on ${label} client: ${err.message}`
+            );
+        });
+    });
+}
+
+export function createPool(
+    connectionString: string,
+    maxConnections: number,
+    idleTimeoutMs: number,
+    connectionTimeoutMs: number,
+    label: string
+): Pool {
+    const pool = new Pool(
+        createPoolConfig(
+            connectionString,
+            maxConnections,
+            idleTimeoutMs,
+            connectionTimeoutMs
+        )
+    );
+    attachPoolErrorHandlers(pool, label);
+    return pool;
+}