rdbms: add an IDatabase method to expose DB server IDs

Bug: T274174
Change-Id: Ia81e64fa99154f43d27bfe070df03686eb4469c5

5 files changed, 47 insertions, 5 deletions

diff --git a/includes/libs/rdbms/database/DBConnRef.php b/includes/libs/rdbms/database/DBConnRef.php
index 335aed8a6037..9e42934df55a 100644
--- a/includes/libs/rdbms/database/DBConnRef.php
+++ b/includes/libs/rdbms/database/DBConnRef.php
@@ -80,6 +80,10 @@ class DBConnRef implements IDatabase {
 		return $this->__call( __FUNCTION__, func_get_args() );
 	}
 
+	public function getTopologyBasedServerId() {
+		return $this->__call( __FUNCTION__, func_get_args() );
+	}
+
 	public function getTopologyRole() {
 		return $this->__call( __FUNCTION__, func_get_args() );
 	}
diff --git a/includes/libs/rdbms/database/Database.php b/includes/libs/rdbms/database/Database.php
index 6992115535d9..31ec74d527d1 100644
--- a/includes/libs/rdbms/database/Database.php
+++ b/includes/libs/rdbms/database/Database.php
@@ -578,6 +578,10 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 		return $this->getServerVersion();
 	}
 
+	public function getTopologyBasedServerId() {
+		return null;
+	}
+
 	public function getTopologyRole() {
 		return $this->topologyRole;
 	}
diff --git a/includes/libs/rdbms/database/DatabaseMysqlBase.php b/includes/libs/rdbms/database/DatabaseMysqlBase.php
index 39ec9b4cbc00..0b613bfaf53a 100644
--- a/includes/libs/rdbms/database/DatabaseMysqlBase.php
+++ b/includes/libs/rdbms/database/DatabaseMysqlBase.php
@@ -1022,9 +1022,14 @@ abstract class DatabaseMysqlBase extends Database {
 		return $pos;
 	}
 
+	public function getTopologyBasedServerId() {
+		// The server_id variable is unique to the replication topology for the dataset
+		return $this->getServerId();
+	}
+
 	/**
-	 * @return int
-	 * @throws DBQueryError If the variable doesn't exist for some reason
+	 * @return int Server ID that is unique to the replication topology and is not reused
+	 * @throws DBQueryError
 	 */
 	protected function getServerId() {
 		$fname = __METHOD__;
@@ -1041,7 +1046,8 @@ abstract class DatabaseMysqlBase extends Database {
 	}
 
 	/**
-	 * @return string|null
+	 * @return string|null Server ID that should be globally unique
+	 * @throws DBQueryError
 	 */
 	protected function getServerUUID() {
 		$fname = __METHOD__;
diff --git a/includes/libs/rdbms/database/DatabaseSqlite.php b/includes/libs/rdbms/database/DatabaseSqlite.php
index 25ef4b74a31a..d514e6171573 100644
--- a/includes/libs/rdbms/database/DatabaseSqlite.php
+++ b/includes/libs/rdbms/database/DatabaseSqlite.php
@@ -739,6 +739,11 @@ class DatabaseSqlite extends Database {
 		return false;
 	}
 
+	public function getTopologyBasedServerId() {
+		// Sqlite topologies trivially consist of single master server for the dataset
+		return 0;
+	}
+
 	public function serverIsReadOnly() {
 		$this->assertHasConnectionHandle();
 
diff --git a/includes/libs/rdbms/database/IDatabase.php b/includes/libs/rdbms/database/IDatabase.php
index dbcaf9c9caad..1be134451718 100644
--- a/includes/libs/rdbms/database/IDatabase.php
+++ b/includes/libs/rdbms/database/IDatabase.php
@@ -164,17 +164,40 @@ interface IDatabase {
 	public function getServerInfo();
 
 	/**
+	 * Get a non-recycled ID that uniquely identifies this server within the replication topology
+	 *
+	 * A replication topology defines which servers can originate changes to a given dataset
+	 * and how those changes propagate among database servers. It is assumed that the server
+	 * only participates in the replication of a single relevant dataset.
+	 *
+	 * @return int|null Unique integer ID; null if not applicable or unknown
+	 * @throws DBQueryError
+	 * @since 1.37
+	 */
+	public function getTopologyBasedServerId();
+
+	/**
 	 * Get the replication topology role of this server
 	 *
+	 * A replication topology defines which servers can originate changes to a given dataset
+	 * and how those changes propagate among database servers. It is assumed that the server
+	 * only participates in the replication of a single relevant dataset.
+	 *
 	 * @return string One of the class ROLE_* constants
+	 * @throws DBQueryError
 	 * @since 1.34
 	 */
 	public function getTopologyRole();
 
 	/**
-	 * Get the host (or address) of the root master server for the replication topology
+	 * Get the readable name of the sole root master server for the replication topology
+	 *
+	 * A replication topology defines which servers can originate changes to a given dataset
+	 * and how those changes propagate among database servers. It is assumed that the server
+	 * only participates in the replication of a single relevant dataset.
 	 *
-	 * @return string|null Master server name or null if not known
+	 * @return string|null Readable server name; null if unknown or if co-masters are defined
+	 * @throws DBQueryError
 	 * @since 1.34
 	 */
 	public function getTopologyRootMaster();