system/Session/Handlers/DatabaseHandler.php
protected function releaseLock(): bool
	{
		if (! $this->lock)
		{
			return true;
		}

		if ($this->platform === 'mysql')
		{
			if ($this->db->query("SELECT RELEASE_LOCK('{$this->lock}') AS ci_session_lock")->getRow()->ci_session_lock)
			{
				$this->lock = false;
				return true;
			}

			return $this->fail();
		}
		elseif ($this->platform === 'postgre')
		{
			if ($this->db->simpleQuery("SELECT pg_advisory_unlock({$this->lock})"))
			{
				$this->lock = false;
				return true;
			}

			return $this->fail();
		}

		// Unsupported DB? Let the parent handle the simple version.
		return parent::releaseLock();
	}
protected function releaseLock(): bool
	{
		if (! $this->lock)
		{
			return true;
		}

		if ($this->platform === 'mysql')
		{
			if ($this->db->query("SELECT RELEASE_LOCK('{$this->lock}') AS ci_session_lock")->getRow()->ci_session_lock)
			{
				$this->lock = false;
				return true;
			}

			return $this->fail();
		}
		elseif ($this->platform === 'postgre')
		{
			if ($this->db->simpleQuery("SELECT pg_advisory_unlock({$this->lock})"))
			{
				$this->lock = false;
				return true;
			}

			return $this->fail();
		}

		// Unsupported DB? Let the parent handle the simple version.
		return parent::releaseLock();
	}
Releases the lock, if any.

@return boolean