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feat: First attempt to track dirty tables after writes and switch back to replicas if reads go to other tables

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Signed-off-by: Julius Härtl <jus@bitgrid.net>

debug: error log

Signed-off-by: Julius Härtl <jus@bitgrid.net>
This commit is contained in:
Julius Härtl 2023-12-15 21:52:31 +01:00
parent 3e60092b7d
commit c17c42a0b2
1 changed files with 27 additions and 0 deletions
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27
lib/private/DB/Connection.php
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@ -81,6 +81,8 @@ class Connection extends PrimaryReadReplicaConnection {
protected ?float $transactionActiveSince = null;
protected $tableDirtyWrites = [];
/**
* Initializes a new instance of the Connection class.
*
@ -257,6 +259,18 @@ class Connection extends PrimaryReadReplicaConnection {
* @throws \Doctrine\DBAL\Exception
*/
public function executeQuery(string $sql, array $params = [], $types = [], QueryCacheProfile $qcp = null): Result {
$tables = $this->getQueriedTables($sql);
if (count(array_intersect($this->tableDirtyWrites, $tables)) === 0 && !$this->isTransactionActive()) {
// No tables read that could have been written already in the same request and no transaction active
// so we can switch back to the replica for reading as long as no writes happen that switch back to the primary
// We cannot log here as this would log too early in the server boot process
$this->ensureConnectedToReplica();
} else {
// Read to a table that was previously written to
// While this might not necessarily mean that we did a read after write it is an indication for a code path to check
$this->logger->debug('dirty table reads: ' . $sql, ['tables' => $this->tableDirtyWrites, 'reads' => $tables, 'exception' => new \Exception()]);
}
$sql = $this->replaceTablePrefix($sql);
$sql = $this->adapter->fixupStatement($sql);
$this->queriesExecuted++;
@ -264,6 +278,16 @@ class Connection extends PrimaryReadReplicaConnection {
return parent::executeQuery($sql, $params, $types, $qcp);
}
/**
* Helper function to get the list of tables affected by a given query
* used to track dirty tables that received a write with the current request
*/
private function getQueriedTables(string $sql): array {
$re = '/(\*PREFIX\*\w+)/mi';
preg_match_all($re, $sql, $matches);
return array_map([$this, 'replaceTablePrefix'], $matches[0] ?? []);
}
/**
* @throws Exception
*/
@ -290,6 +314,9 @@ class Connection extends PrimaryReadReplicaConnection {
* @throws \Doctrine\DBAL\Exception
*/
public function executeStatement($sql, array $params = [], array $types = []): int {
$tables = $this->getQueriedTables($sql);
$this->tableDirtyWrites = array_unique(array_merge($this->tableDirtyWrites, $tables));
$this->logger->debug('dirty table writes: ' . $sql, ['tables' => $this->tableDirtyWrites]);
$sql = $this->replaceTablePrefix($sql);
$sql = $this->adapter->fixupStatement($sql);
$this->queriesExecuted++;