make build concurrency configurable

src/node/build/build.ts

@@ -123,7 +123,7 @@ export async function build(
             additionalHeadTags
           )
         },
-        { concurrency: 64 }
+        { concurrency: siteConfig.buildConcurrency }
       )
     })
 

src/node/config.ts

@@ -141,7 +141,8 @@ export async function resolveConfig(
     transformPageData: userConfig.transformPageData,
     rewrites,
     userConfig,
-    sitemap: userConfig.sitemap
+    sitemap: userConfig.sitemap,
+    buildConcurrency: userConfig.buildConcurrency ?? 64
   }
 
   // to be shared with content loaders

src/node/siteConfig.ts

@@ -147,6 +147,15 @@ export interface UserConfig<ThemeConfig = any>
    */
   useWebFonts?: boolean
 
+  /**
+   * This option allows you to configure the concurrency of the build.
+   * A lower number will reduce the memory usage but will increase the build time.
+   *
+   * @experimental
+   * @default 64
+   */
+  buildConcurrency?: number
+
   /**
    * @experimental
    *
@@ -240,4 +249,5 @@ export interface SiteConfig<ThemeConfig = any>
   }
   logger: Logger
   userConfig: UserConfig
+  buildConcurrency: number
 }