Moodle: MySQL connection times out under HHVM, but not Zend

[csvan]

Environment
Ubuntu 14.04
HHVM 3.1 (from repo)
PHP 5.5.9
MySQL 5.5
Moodle 2.8 dev

Scenario

Set up test environment (http://docs.moodle.org/dev/PHPUnit).

Run the following test class:
https://github.com/moodle/moodle/blob/master/question/engine/tests/questionusage_autosave_test.php

by executing:

vendor/bin/phpunit --debug question_usage_autosave_test question/engine/tests/questionusage_autosave_test.php

Do the above both for PHP and HHVM.

Outcome
Tests pass fine under PHP in reasonable time (11 seconds on my machine). Running under HHVM takes several minutes and eventually crashes due to the database connection timing out. See output for both runtimes below:

PHP

Starting test 'question_usage_autosave_test::test_autosave_then_display'.
Starting test 'question_usage_autosave_test::test_autosave_then_autosave_different_data'.
Starting test 'question_usage_autosave_test::test_autosave_then_autosave_same_data'.
Starting test 'question_usage_autosave_test::test_autosave_then_autosave_original_data'.
Starting test 'question_usage_autosave_test::test_autosave_then_real_save'.
Starting test 'question_usage_autosave_test::test_autosave_then_real_save_same'.
Starting test 'question_usage_autosave_test::test_autosave_then_submit'.
Starting test 'question_usage_autosave_test::test_autosave_and_save_concurrently'.
Starting test 'question_usage_autosave_test::test_concurrent_autosaves'.
Starting test 'question_usage_autosave_test::test_autosave_with_wrong_seq_number_ignored'.
Starting test 'question_usage_autosave_test::test_finish_with_unhandled_autosave_data'.
Time: 11.11 seconds, Memory: 61.25Mb

HHVM

Starting test 'question_usage_autosave_test::test_autosave_then_display'.
Starting test 'question_usage_autosave_test::test_autosave_then_autosave_different_data'.
Starting test 'question_usage_autosave_test::test_autosave_then_autosave_same_data'.
Starting test 'question_usage_autosave_test::test_autosave_then_autosave_original_data'.
Starting test 'question_usage_autosave_test::test_autosave_then_real_save'.
Starting test 'question_usage_autosave_test::test_autosave_then_real_save_same'.
Starting test 'question_usage_autosave_test::test_autosave_then_submit'.
Starting test 'question_usage_autosave_test::test_autosave_and_save_concurrently'.
.
Starting test 'question_usage_autosave_test::test_concurrent_autosaves'.
SlowTimer [51966ms] at runtime/ext_mysql: slow query: DELETE FROM phpunit_question_attempt_steps 
E
Starting test 'question_usage_autosave_test::test_autosave_with_wrong_seq_number_ignored'.
SlowTimer [50446ms] at runtime/ext_mysql: slow query: DELETE FROM phpunit_question_attempt_steps 
E
Starting test 'question_usage_autosave_test::test_finish_with_unhandled_autosave_data'.
SlowTimer [50786ms] at runtime/ext_mysql: slow query: DELETE FROM phpunit_question_attempt_steps 
ESlowTimer [50996ms] at runtime/ext_mysql: slow query: DELETE FROM phpunit_question_attempt_steps 

Fatal error: Uncaught exception 'dml_write_exception' with message 'Error writing to database (Lock wait timeout exceeded; try restarting transaction
DELETE FROM phpunit_question_attempt_steps 
[array (
)])' in /home/christopher/sandbox/moodle/lib/dml/moodle_database.php:446
Stack trace:
#0 /home/christopher/sandbox/moodle/lib/dml/mysqli_native_moodle_database.php(1423): moodle_database->query_end()
#1 /home/christopher/sandbox/moodle/lib/dml/moodle_database.php(1829): mysqli_native_moodle_database->delete_records_select()
#2 /home/christopher/sandbox/moodle/lib/testing/classes/util.php(629): moodle_database->delete_records()
#3 /home/christopher/sandbox/moodle/lib/phpunit/classes/util.php(269): testing_util::reset_database()
#4 /home/christopher/sandbox/moodle/lib/phpunit/classes/util.php(130): phpunit_util::reset_database()
#5 /home/christopher/sandbox/moodle/lib/phpunit/classes/advanced_testcase.php(449): phpunit_util::reset_all_data()
#6 /home/christopher/sandbox/moodle/vendor/phpunit/phpunit/PHPUnit/Framework/TestSuite.php(760): advanced_testcase::tearDownAfterClass()
#7 /home/christopher/sandbox/moodle/vendor/phpunit/phpunit/PHPUnit/TextUI/TestRunner.php(350): PHPUnit_Framework_TestSuite->run()
#8 /home/christopher/sandbox/moodle/vendor/phpunit/phpunit/PHPUnit/TextUI/Command.php(176): PHPUnit_TextUI_TestRunner->doRun()
#9 /home/christopher/sandbox/moodle/vendor/phpunit/phpunit/PHPUnit/TextUI/Command.php(129): PHPUnit_TextUI_Command->run()
#10 /home/christopher/sandbox/moodle/vendor/phpunit/phpunit/composer/bin/phpunit(63): PHPUnit_TextUI_Command::main()
#11 {main}

[lexidor]

I am going over old issues on this repository, to see which ones apply to the current versions of hhvm.

This issue applies to running php code on hhvm. Hhvm nolonger supports running php code since hhvm version 4.0.0.

Moodle is a PHP application.