Catch and ignore UniqueConstraintViolationException in file locking init

[MorrisJobke]

• caused by a concurrect insert that happens between the INSERT and it's sub-SELECT which was there to actually avoid it within insertIfNotExists - sub selects are not atomic and allow this
• see also Bug 6160: Deadlock removed #12315
• fixes Race condition with locks in database - unique constraint violation on oc_file_locks #9305, fixes Serialization failure: 1213 Deadlock found when trying to get lock; try restarting transaction #6899
• improved version of Bug 6160: Deadlock removed #12315
• part of UniqueConstraintViolationException overview ticket #12369

Avoids an error that has this stack trace:

Doctrine\DBAL\Exception\UniqueConstraintViolationException

An exception occurred while executing 'INSERT INTO "oc_file_locks" ("key","lock","ttl") SELECT ?,?,? FROM "oc_file_locks" WHERE "key" = ? HAVING COUNT(*) = 0' with params ["files/737d52477f1fb583a5bfe5eb33e820da", 1, 1524066628, "files/737d52477f1fb583a5bfe5eb33e820da"]:

SQLSTATE[23505]: Unique violation: 7 ERROR:  duplicate key value violates unique constraint "lock_key_index"
DETAIL:  Key (key)=(files/737d52477f1fb583a5bfe5eb33e820da) already exists.

 #0 3rdparty/doctrine/dbal/lib/Doctrine/DBAL/DBALException.php(128): Doctrine\DBAL\Driver\AbstractPostgreSQLDriver->convertException('An exception oc...', Object(Doctrine\DBAL\Driver\PDOException))
 #1 3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(1015): Doctrine\DBAL\DBALException::driverExceptionDuringQuery(Object(Doctrine\DBAL\Driver\PDOPgSql\Driver), Object(Doctrine\DBAL\Driver\PDOException), 'INSERT INTO "oc...', Array)
 #2 lib/private/DB/Connection.php(213): Doctrine\DBAL\Connection->executeUpdate('INSERT INTO "oc...', Array, Array)
 #3 lib/private/DB/Adapter.php(114): OC\DB\Connection->executeUpdate('INSERT INTO "oc...', Array)
 #4 lib/private/DB/Connection.php(251): OC\DB\Adapter->insertIfNotExist('*PREFIX*file_lo...', Array, Array)
 #5 lib/private/Lock/DBLockingProvider.php(118): OC\DB\Connection->insertIfNotExist('*PREFIX*file_lo...', Array, Array)
 #6 lib/private/Lock/DBLockingProvider.php(163): OC\Lock\DBLockingProvider->initLockField('files/737d52477...', 1)
 #7 lib/private/Files/Storage/Common.php(704): OC\Lock\DBLockingProvider->acquireLock('files/737d52477...', 1)
 #8 lib/private/Files/View.php(1931): OC\Files\Storage\Common->acquireLock('files/Documents', 1, Object(OC\Lock\DBLockingProvider))
 #9 lib/private/Files/View.php(2041): OC\Files\View->lockPath('/*******/files/...', 1, false)
 #10 lib/private/Files/Node/Node.php(360): OC\Files\View->lockFile('/*******/files/...', 1)
 #11 apps/files_sharing/lib/Controller/ShareAPIController.php(928): OC\Files\Node\Node->lock(1)
 #12 apps/files_sharing/lib/Controller/ShareAPIController.php(589): OCA\Files_Sharing\Controller\ShareAPIController->lock(Object(OC\Files\Node\Folder))
 #13 [internal function]: OCA\Files_Sharing\Controller\ShareAPIController->getShares('true', 'false', 'false', Object(OC\Files\Node\Folder), 'false')
 #14 lib/private/AppFramework/Http/Dispatcher.php(160): call_user_func_array(Array, Array)
 #15 lib/private/AppFramework/Http/Dispatcher.php(90): OC\AppFramework\Http\Dispatcher->executeController(Object(OCA\Files_Sharing\Controller\ShareAPIController), 'getShares')
 #16 lib/private/AppFramework/App.php(114): OC\AppFramework\Http\Dispatcher->dispatch(Object(OCA\Files_Sharing\Controller\ShareAPIController), 'getShares')
 #17 lib/private/AppFramework/Routing/RouteActionHandler.php(47): OC\AppFramework\App::main('OCA\\Files_Shari...', 'getShares', Object(OC\AppFramework\DependencyInjection\DIContainer), Array)
 #18 [internal function]: OC\AppFramework\Routing\RouteActionHandler->__invoke(Array)
 #19 lib/private/Route/Router.php(299): call_user_func(Object(OC\AppFramework\Routing\RouteActionHandler), Array)
 #20 ocs/v1.php(78): OC\Route\Router->match('/ocsapp/apps/fi...')
 #21 ocs/v2.php(23): require_once('/usr/share/weba...')
 #22 {main}

@obel1x Please have a look at this.

[MorrisJobke]

@matt-horwood-mayden @Temtaime @OneOfOne @jirutka Could you test if this fixes the issues that you are seeing in #9305?

[MorrisJobke]

@mxschmitt @martinber Could you check if this fixes the issues you had in #9305?

[kesselb]

I would prefer insert instead of insertIfNotExists here.

1. There should be an unique index

   server/core/Migrations/Version13000Date20170718121200.php

   Line 705 in b82cbe0

   $table->addUniqueIndex(['key'], 'lock_key_index');

2. https://dev.mysql.com/doc/refman/8.0/en/insert-select.html

The target table of the INSERT statement may appear in the FROM clause of the SELECT part of the query. However, you cannot insert into a table and select from the same table in a subquery. When selecting from and inserting into the same table, MySQL creates an internal temporary table to hold the rows from the SELECT and then inserts those rows into the target table. However, you cannot use INSERT INTO t ... SELECT ... FROM t when t is a TEMPORARY table, because TEMPORARY tables cannot be referred to twice in the same statement.

I guess a temporary table with a few records is not that bad. But for the use case (as far as i understand it) you dont need it?

Maybe I'm missing something but when you catch the UniqueConstraintViolationException anyway this "fake" atomic insert is not required anymore?

[MorrisJobke]

Let's go for #12371, which addresses the first comment of @danielkesselberg and was also the feedback from other developers on IRC.