rdbms: fix connection reuse logic in LoadBalancer for postgres

Change-Id: Ic4b7af156fbed54aae0a34a0bbba76490cd505e0

diff --git a/includes/libs/rdbms/loadbalancer/LoadBalancer.php b/includes/libs/rdbms/loadbalancer/LoadBalancer.php
index 1f3fe4c..d157a23 100644 (file)
--- a/includes/libs/rdbms/loadbalancer/LoadBalancer.php
+++ b/includes/libs/rdbms/loadbalancer/LoadBalancer.php
@@ -1001,6 +1001,8 @@ class LoadBalancer implements ILoadBalancer {
                }
 
                /** @var Database $conn */
+               $conn = null;
+
                if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
                        // Reuse an in-use connection for the same domain
                        $conn = $this->conns[$connInUseKey][$i][$domain];
@@ -1012,22 +1014,36 @@ class LoadBalancer implements ILoadBalancer {
                        $this->conns[$connInUseKey][$i][$domain] = $conn;
                        $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
                } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
-                       // Reuse a free connection from another domain
-                       $conn = reset( $this->conns[$connFreeKey][$i] );
-                       $oldDomain = key( $this->conns[$connFreeKey][$i] );
-                       if ( $domainInstance->getDatabase() !== null ) {
-                               $conn->selectDomain( $domainInstance );
-                       } else {
-                               // Stay on the current database, but update the schema/prefix
-                               $conn->dbSchema( $domainInstance->getSchema() );
-                               $conn->tablePrefix( $domainInstance->getTablePrefix() );
+                       // Reuse a free connection from another domain if possible
+                       foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
+                               if ( $domainInstance->getDatabase() !== null ) {
+                                       // Check if changing the database will require a new connection.
+                                       // In that case, leave the connection handle alone and keep looking.
+                                       // This prevents connections from being closed mid-transaction and can
+                                       // also avoid overhead if the same database will later be requested.
+                                       if (
+                                               $conn->databasesAreIndependent() &&
+                                               $conn->getDBname() !== $domainInstance->getDatabase()
+                                       ) {
+                                               continue;
+                                       }
+                                       // Select the new database, schema, and prefix
+                                       $conn->selectDomain( $domainInstance );
+                               } else {
+                                       // Stay on the current database, but update the schema/prefix
+                                       $conn->dbSchema( $domainInstance->getSchema() );
+                                       $conn->tablePrefix( $domainInstance->getTablePrefix() );
+                               }
+                               unset( $this->conns[$connFreeKey][$i][$oldDomain] );
+                               // Note that if $domain is an empty string, getDomainID() might not match it
+                               $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
+                               $this->connLogger->debug( __METHOD__ .
+                                       ": reusing free connection from $oldDomain for $domain" );
+                               break;
                        }
-                       unset( $this->conns[$connFreeKey][$i][$oldDomain] );
-                       // Note that if $domain is an empty string, getDomainID() might not match it
-                       $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
-                       $this->connLogger->debug( __METHOD__ .
-                               ": reusing free connection from $oldDomain for $domain" );
-               } else {
+               }
+
+               if ( !$conn ) {
                        if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
                                throw new InvalidArgumentException( "No server with index '$i'." );
                        }