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authorPierre Schmitz <pierre@archlinux.de>2013-01-18 16:46:04 +0100
committerPierre Schmitz <pierre@archlinux.de>2013-01-18 16:46:04 +0100
commit63601400e476c6cf43d985f3e7b9864681695ed4 (patch)
treef7846203a952e38aaf66989d0a4702779f549962 /includes/dao/IDBAccessObject.php
parent8ff01378c9e0207f9169b81966a51def645b6a51 (diff)
Update to MediaWiki 1.20.2
this update includes: * adjusted Arch Linux skin * updated FluxBBAuthPlugin * patch for https://bugzilla.wikimedia.org/show_bug.cgi?id=44024
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+<?php
+/**
+ * This file contains database access object related constants.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ * @ingroup Database
+ */
+
+/**
+ * Interface for database access objects.
+ *
+ * Classes using this support a set of constants in a bitfield argument to their data loading
+ * functions. In general, objects should assume READ_NORMAL if no flags are explicitly given,
+ * though certain objects may assume READ_LATEST for common use case or legacy reasons.
+ *
+ * There are three types of reads:
+ * - READ_NORMAL : Potentially cached read of data (e.g. from a slave or stale replica)
+ * - READ_LATEST : Up-to-date read as of transaction start (e.g. from master or a quorum read)
+ * - READ_LOCKING : Up-to-date read as of now, that locks the records for the transaction
+ *
+ * Callers should use READ_NORMAL (or pass in no flags) unless the read determines a write.
+ * In theory, such cases may require READ_LOCKING, though to avoid contention, READ_LATEST is
+ * often good enough. If UPDATE race condition checks are required on a row and expensive code
+ * must run after the row is fetched to determine the UPDATE, it may help to do something like:
+ * - a) Read the current row
+ * - b) Determine the new row (expensive, so we don't want to hold locks now)
+ * - c) Re-read the current row with READ_LOCKING; if it changed then bail out
+ * - d) otherwise, do the updates
+ */
+interface IDBAccessObject {
+ // Constants for object loading bitfield flags (higher => higher QoS)
+ const READ_LATEST = 1; // read from the master
+ const READ_LOCKING = 3; // READ_LATEST and "FOR UPDATE"
+
+ // Convenience constant for callers to explicitly request slave data
+ const READ_NORMAL = 0; // read from the slave
+
+ // Convenience constant for tracking how data was loaded (higher => higher QoS)
+ const READ_NONE = -1; // not loaded yet (or the object was cleared)
+}