rdbms: clear replica snapshots in (begin|commit|rollback)PrimaryChanges()

Automatically perform the empty-transaction commit logic in methods
like beginPrimaryChanges() and commitPrimaryChanges(). This avoids
the proliferation of callers having to call the same set of methods
one after another for non-obvious reasons. It also discourages code
from making brittle assumptions that might fail for setups where
there is only a primary or the primary has non-zero read load.

Deprecate flushReplicaSnapshots() and remove callers.

Clarify the related method documentation.

Bug: T315664
Change-Id: I255afd22ffcaeac0fad2d4e4a2a0c55c99be7905

3 files changed, 24 insertions, 2 deletions

diff --git a/tests/phpunit/includes/db/LBFactoryTest.php b/tests/phpunit/includes/db/LBFactoryTest.php
index f3390aada00d..a437a8408bfd 100644
--- a/tests/phpunit/includes/db/LBFactoryTest.php
+++ b/tests/phpunit/includes/db/LBFactoryTest.php
@@ -191,6 +191,29 @@ class LBFactoryTest extends MediaWikiIntegrationTestCase {
 		$factory->closeAll( __METHOD__ );
 	}
 
+	public function testLBFactoryMultiRoundTransactionSnapshots() {
+		$factory = $this->newLBFactoryMultiLBs();
+		$dbr = $factory->getMainLB()->getConnection( DB_REPLICA );
+		$dbw = $factory->getMainLB()->getConnection( DB_PRIMARY );
+
+		$dbr->begin( __METHOD__, $dbr::TRANSACTION_INTERNAL );
+		$this->assertSame( 1, $dbr->trxLevel() );
+		$this->assertSame( 0, $dbw->trxLevel() );
+
+		$factory->beginPrimaryChanges( __METHOD__ );
+		$this->assertSame( 0, $dbr->trxLevel() );
+		$this->assertSame( 0, $dbw->trxLevel() );
+
+		$dbr->begin( __METHOD__, $dbr::TRANSACTION_INTERNAL );
+		$dbw->begin( __METHOD__, $dbw::TRANSACTION_INTERNAL );
+		$this->assertSame( 1, $dbr->trxLevel() );
+		$this->assertSame( 1, $dbw->trxLevel() );
+
+		$factory->commitPrimaryChanges( __METHOD__ );
+		$this->assertSame( 0, $dbr->trxLevel() );
+		$this->assertSame( 0, $dbw->trxLevel() );
+	}
+
 	private function newLBFactoryMultiLBs() {
 		global $wgDBserver, $wgDBport, $wgDBname, $wgDBuser, $wgDBpassword, $wgDBtype;
 		global $wgSQLiteDataDir;
diff --git a/tests/phpunit/includes/deferred/DeferredUpdatesTest.php b/tests/phpunit/includes/deferred/DeferredUpdatesTest.php
index 47d2533099dc..6faedf679a89 100644
--- a/tests/phpunit/includes/deferred/DeferredUpdatesTest.php
+++ b/tests/phpunit/includes/deferred/DeferredUpdatesTest.php
@@ -354,7 +354,6 @@ class DeferredUpdatesTest extends MediaWikiIntegrationTestCase {
 		DeferredUpdates::attemptUpdate(
 			new MWCallableUpdate(
 				static function () use ( $lbFactory, $fname, &$called ) {
-					$lbFactory->flushReplicaSnapshots( $fname );
 					$lbFactory->commitPrimaryChanges( $fname );
 					$called = true;
 				},
diff --git a/tests/phpunit/integration/includes/db/DatabaseMysqlTest.php b/tests/phpunit/integration/includes/db/DatabaseMysqlTest.php
index 39a8fdb05610..d1a400e27521 100644
--- a/tests/phpunit/integration/includes/db/DatabaseMysqlTest.php
+++ b/tests/phpunit/integration/includes/db/DatabaseMysqlTest.php
@@ -197,7 +197,7 @@ class DatabaseMysqlTest extends \MediaWikiIntegrationTestCase {
 
 		// Get a lock outside of any transaction
 		$unlocker = $this->conn->getScopedLockAndFlush( 'testing-key', __METHOD__, 0 );
-		// Start transaction *after* getting the lock
+		// Start transaction after getting the lock
 		$this->conn->begin( __METHOD__, IDatabase::TRANSACTION_INTERNAL );
 
 		$row = $this->conn->query( 'SELECT connection_id() AS id', __METHOD__ )->fetchObject();