Add comments to ApiBase::isWriteMode()

Change-Id: I3581f5e3055c425367d265a5c57831bb34dd5a2f

diff --git a/includes/api/ApiBase.php b/includes/api/ApiBase.php
index b698cef..37750c8 100644 (file)
--- a/includes/api/ApiBase.php
+++ b/includes/api/ApiBase.php
@@ -385,6 +385,13 @@ abstract class ApiBase extends ContextSource {
 
        /**
         * Indicates whether this module requires write mode
+        *
+        * This should return true for modules that may require synchronous database writes.
+        * Modules that do not need such writes should also not rely on master database access,
+        * since only read queries are needed and each master DB is a single point of failure.
+        * Additionally, requests that only need replica DBs can be efficiently routed to any
+        * datacenter via the Promise-Non-Write-API-Action header.
+        *
         * @return bool
         */
        public function isWriteMode() {