From 0222778a3669ba7c735ff256877c57fb35e37562 Mon Sep 17 00:00:00 2001
From: Andrey Avtomonov <andreybavt@gmail.com>
Date: Sun, 24 May 2026 00:57:36 +0200
Subject: [PATCH] feat(connectors): add mysql maxConnections

---
 .../src/connectors/mysql/connector.test.ts    | 42 ++++++++++++++++++-
 .../cli/src/connectors/mysql/connector.ts     | 26 +++++++++++-
 2 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/packages/cli/src/connectors/mysql/connector.test.ts b/packages/cli/src/connectors/mysql/connector.test.ts
index 5a21ada7..fbf898bc 100644
--- a/packages/cli/src/connectors/mysql/connector.test.ts
+++ b/packages/cli/src/connectors/mysql/connector.test.ts
@@ -1,7 +1,7 @@
 import { describe, expect, it, vi } from 'vitest';
 import type { FieldPacket, RowDataPacket } from 'mysql2/promise';
 import { createMysqlLiveDatabaseIntrospection } from '../../connectors/mysql/live-database-introspection.js';
-import { isKtxMysqlConnectionConfig, KtxMysqlScanConnector, mysqlConnectionPoolConfigFromConfig, type KtxMysqlPoolFactory } from '../../connectors/mysql/connector.js';
+import { isKtxMysqlConnectionConfig, KtxMysqlScanConnector, mysqlConnectionPoolConfigFromConfig, type KtxMysqlConnectionConfig, type KtxMysqlPoolFactory } from '../../connectors/mysql/connector.js';
 import { tableRefSet } from '../../context/scan/table-ref.js';
 
 function mysqlResult(rows: Record<string, unknown>[], fields: Array<{ name: string; type?: number }>): [RowDataPacket[], FieldPacket[]] {
@@ -191,6 +191,46 @@ describe('KtxMysqlScanConnector', () => {
     });
   });
 
+  it('defaults and validates MySQL maxConnections', () => {
+    const baseConnection: KtxMysqlConnectionConfig = {
+      driver: 'mysql',
+      host: 'db.example.test',
+      database: 'analytics',
+      username: 'reader',
+      password: 'secret', // pragma: allowlist secret
+    };
+
+    expect(
+      mysqlConnectionPoolConfigFromConfig({
+        connectionId: 'warehouse',
+        connection: baseConnection,
+      }),
+    ).toMatchObject({ connectionLimit: 10 });
+
+    expect(
+      mysqlConnectionPoolConfigFromConfig({
+        connectionId: 'warehouse',
+        connection: { ...baseConnection, maxConnections: 25 },
+      }),
+    ).toMatchObject({ connectionLimit: 25 });
+
+    expect(
+      mysqlConnectionPoolConfigFromConfig({
+        connectionId: 'warehouse',
+        connection: { ...baseConnection, maxConnections: '12' as never },
+      }),
+    ).toMatchObject({ connectionLimit: 12 });
+
+    for (const maxConnections of [0, -1, 1.5, Number.NaN, 'abc' as never]) {
+      expect(() =>
+        mysqlConnectionPoolConfigFromConfig({
+          connectionId: 'warehouse',
+          connection: { ...baseConnection, maxConnections },
+        }),
+      ).toThrow('connections.warehouse.maxConnections must be a positive integer');
+    }
+  });
+
   it('introspects schema, primary keys, comments, row counts, views, and foreign keys', async () => {
     const connector = new KtxMysqlScanConnector({
       connectionId: 'warehouse',
diff --git a/packages/cli/src/connectors/mysql/connector.ts b/packages/cli/src/connectors/mysql/connector.ts
index 82a2384c..7e299dab 100644
--- a/packages/cli/src/connectors/mysql/connector.ts
+++ b/packages/cli/src/connectors/mysql/connector.ts
@@ -18,6 +18,7 @@ export interface KtxMysqlConnectionConfig {
   password?: string;
   url?: string;
   ssl?: boolean | { rejectUnauthorized?: boolean };
+  maxConnections?: number;
   [key: string]: unknown;
 }
 
@@ -163,6 +164,23 @@ function maybeNumber(value: unknown): number | undefined {
   return typeof value === 'number' && Number.isFinite(value) ? value : undefined;
 }
 
+function positiveIntegerConfigValue(input: {
+  connection: KtxMysqlConnectionConfig;
+  key: keyof KtxMysqlConnectionConfig;
+  connectionId: string;
+  defaultValue: number;
+}): number {
+  const value = input.connection[input.key];
+  if (value === undefined) {
+    return input.defaultValue;
+  }
+  const numberValue = Number(value);
+  if (!Number.isInteger(numberValue) || numberValue < 1) {
+    throw new Error(`connections.${input.connectionId}.${String(input.key)} must be a positive integer`);
+  }
+  return numberValue;
+}
+
 function parseMysqlUrl(url: string): Partial<KtxMysqlConnectionConfig> {
   const parsed = new URL(url);
   const sslParam = parsed.searchParams.get('ssl') ?? parsed.searchParams.get('sslmode');
@@ -262,6 +280,12 @@ export function mysqlConnectionPoolConfigFromConfig(input: {
   const host = stringConfigValue(merged, 'host', env);
   const database = stringConfigValue(merged, 'database', env);
   const user = stringConfigValue(merged, 'username', env) ?? stringConfigValue(merged, 'user', env);
+  const maxConnections = positiveIntegerConfigValue({
+    connection: merged,
+    key: 'maxConnections',
+    connectionId: input.connectionId,
+    defaultValue: 10,
+  });
 
   if (!host) {
     throw new Error(`Native MySQL connector requires connections.${input.connectionId}.host or url`);
@@ -280,7 +304,7 @@ export function mysqlConnectionPoolConfigFromConfig(input: {
     database,
     user,
     password: stringConfigValue(merged, 'password', env),
-    connectionLimit: 10,
+    connectionLimit: maxConnections,
     waitForConnections: true,
     ...(ssl ? { ssl: { rejectUnauthorized: ssl.rejectUnauthorized ?? false } } : {}),
   };