Move jit mode to a config param

Ref #3262

server/db/pg/poolConfig.ts

@@ -1,3 +1,4 @@
+import config from "@server/lib/config";
 import { Pool, PoolConfig } from "pg";
 
 export function createPoolConfig(
@@ -18,17 +19,7 @@ export function createPoolConfig(
         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,
-        // Disable JIT compilation for this connection. Our hot-path queries
-        // (e.g. resource-by-domain lookups) join many tables but only ever
-        // return a handful of rows. When planner row estimates drift (e.g.
-        // due to autovacuum lag under write-heavy load), Postgres decides
-        // these plans are expensive enough to JIT-compile, which can add
-        // multiple seconds of pure compilation overhead per query and
-        // saturate the connection pool. JIT never pays off for these
-        // short-lived OLTP queries, so it's disabled outright rather than
-        // relying on statistics staying fresh.
-        options: "-c jit=off"
+        allowExitOnIdle: false
     };
 }
 
@@ -49,6 +40,28 @@ export function attachPoolErrorHandlers(pool: Pool, label: string): void {
                 `Failed to set statement_timeout on ${label} client: ${err.message}`
             );
         });
+
+        // Disable JIT compilation for this connection. Our hot-path queries
+        // (e.g. resource-by-domain lookups) join many tables but only ever
+        // return a handful of rows. When planner row estimates drift (e.g.
+        // due to autovacuum lag under write-heavy load), Postgres decides
+        // these plans are expensive enough to JIT-compile, which can add
+        // multiple seconds of pure compilation overhead per query and
+        // saturate the connection pool. JIT never pays off for these
+        // short-lived OLTP queries, so it's disabled outright rather than
+        // relying on statistics staying fresh.
+        //
+        // Set via a runtime SET command rather than the `options: "-c
+        // jit=off"` startup parameter: connections in SaaS mode go through
+        // a pooler (e.g. PgBouncer) that rejects arbitrary startup packet
+        // options with a protocol_violation (08P01) error.
+        if (config.getRawConfig().postgres?.pool.jit_mode == false) {
+            client.query("SET jit = off").catch((err: Error) => {
+                console.warn(
+                    `Failed to set jit=off on ${label} client: ${err.message}`
+                );
+            });
+        }
     });
 }