Commit 37fcdbc6 authored by webchick's avatar webchick

#633678 by Josh Waihi, chx, Crell, David Strauss, and Damien Tournoud: Make...

#633678 by Josh Waihi, chx, Crell, David Strauss, and Damien Tournoud: Make sequence API work on non-MySQL databases.
parent 39f4d724
......@@ -1178,26 +1178,7 @@ public function commit() {
* An integer number larger than any number returned by earlier calls and
* also larger than the $existing_id if one was passed in.
*/
public function nextId($existing_id = 0) {
$transaction = $this->startTransaction();
// We can safely use literal queries here instead of the slower query
// builder because if a given database breaks here then it can simply
// override nextId. However, this is unlikely as we deal with short strings
// and integers and no known databases require special handling for those
// simple cases. If another transaction wants to write the same row, it will
// wait until this transaction commits.
$stmt = $this->query('UPDATE {sequences} SET value = GREATEST(value, :existing_id) + 1', array(
':existing_id' => $existing_id,
));
if (!$stmt->rowCount()) {
$this->query('INSERT INTO {sequences} (value) VALUES (:existing_id + 1)', array(
':existing_id' => $existing_id,
));
}
// The transaction gets committed when the transaction object gets destroyed
// because it gets out of scope.
return $new_value;
}
abstract public function nextId($existing_id = 0);
}
/**
......
......@@ -11,6 +11,11 @@
* @{
*/
/**
* The name by which to obtain a lock for retrive the next insert id.
*/
define('POSTGRESQL_NEXTID_LOCK', 1000);
class DatabaseConnection_pgsql extends DatabaseConnection {
public function __construct(array $connection_options = array()) {
......@@ -127,6 +132,49 @@ public function mapConditionOperator($operator) {
return isset($specials[$operator]) ? $specials[$operator] : NULL;
}
/**
* Retrive a the next id in a sequence.
*
* PostgreSQL has built in sequences. We'll use these instead of inserting
* and updating a sequences table.
*/
public function nextId($existing = 0) {
// Retrive the name of the sequence. This information cannot be cached
// because the prefix may change, for example, like it does in simpletests.
$sequence_name = $this->makeSequenceName('sequences', 'value');
// When PostgreSQL gets a value too small then it will lock the table,
// retry the INSERT and if it's still too small then alter the sequence.
$id = $this->query("SELECT nextval('" . $sequence_name . "')")->fetchField();
if ($id > $existing) {
return $id;
}
// PostgreSQL advisory locks are simply locks to be used by an
// application such as Drupal. This will prevent other Drupal proccesses
// from altering the sequence while we are.
$this->query("SELECT pg_advisory_lock(" . POSTGRESQL_NEXTID_LOCK . ")");
// While waiting to obtain the lock, the sequence may have been altered
// so lets try again to obtain an adequate value.
$id = $this->query("SELECT nextval('" . $sequence_name . "')")->fetchField();
if ($id > $existing) {
$this->query("SELECT pg_advisory_unlock(" . POSTGRESQL_NEXTID_LOCK . ")");
return $id;
}
// Reset the sequence to a higher value than the existing id.
$this->query("ALTER SEQUENCE " . $sequence_name . " RESTART WITH " . ($existing + 1));
// Retrive the next id. We know this will be as high as we want it.
$id = $this->query("SELECT nextval('" . $sequence_name . "')")->fetchField();
$this->query("SELECT pg_advisory_unlock(" . POSTGRESQL_NEXTID_LOCK . ")");
return $id;
}
}
/**
......
......@@ -167,6 +167,27 @@ public function prepareQuery($query, $cache = TRUE) {
// DatabaseStatement_sqlite::execute() and cannot be cached.
return $this->prepare($this->prefixTables($query));
}
public function nextId($existing_id = 0) {
$transaction = $this->startTransaction();
// We can safely use literal queries here instead of the slower query
// builder because if a given database breaks here then it can simply
// override nextId. However, this is unlikely as we deal with short strings
// and integers and no known databases require special handling for those
// simple cases. If another transaction wants to write the same row, it will
// wait until this transaction commits.
$stmt = $this->query('UPDATE {sequences} SET value = GREATEST(value, :existing_id) + 1', array(
':existing_id' => $existing_id,
));
if (!$stmt->rowCount()) {
$this->query('INSERT INTO {sequences} (value) VALUES (:existing_id + 1)', array(
':existing_id' => $existing_id,
));
}
// The transaction gets committed when the transaction object gets destroyed
// because it gets out of scope.
return $new_value;
}
}
/**
......
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