Fix Bug #28344 - “Links doesn't work inside collapsible toggles”

[lhc/web/wiklou.git] / docs / database.txt

diff --git a/docs/database.txt b/docs/database.txt
index 679492a..3985b70 100644 (file)
--- a/docs/database.txt
+++ b/docs/database.txt
@@ -2,28 +2,30 @@ Some information about database access in MediaWiki.
 By Tim Starling, January 2006.
 
 ------------------------------------------------------------------------
-    API
+    Database layout
 ------------------------------------------------------------------------
 
-For a database API reference, please see the auto-generated
-documentation:
+For information about the MediaWiki database layout, such as a 
+description of the tables and their contents, please see:
+  http://www.mediawiki.org/wiki/Manual:Database_layout
+  http://svn.wikimedia.org/viewvc/mediawiki/trunk/phase3/maintenance/tables.sql?view=markup
+
 
-http://wikipedia.sourceforge.net/doc/MediaWiki/Database.html
+------------------------------------------------------------------------
+    API
+------------------------------------------------------------------------
 
 To make a read query, something like this usually suffices:
 
-$dbr =& wfGetDB( DB_SLAVE );
+$dbr = wfGetDB( DB_SLAVE );
 $res = $dbr->select( /* ...see docs... */ );
-while ( $row = $dbr->fetchObject( $res ) ) {
+foreach ( $res as $row ) {
        ...
 }
-$dbr->freeResult( $res );
-
-Note the assignment operator in the while condition.
 
 For a write query, use something like:
 
-$dbw =& wfGetDB( DB_MASTER );
+$dbw = wfGetDB( DB_MASTER );
 $dbw->insert( /* ...see docs... */ );
 
 We use the convention $dbr for read and $dbw for write to help you keep
@@ -69,7 +71,7 @@ want to write code destined for Wikipedia.
 It's often the case that the best algorithm to use for a given task
 depends on whether or not replication is in use. Due to our unabashed
 Wikipedia-centrism, we often just use the replication-friendly version,
-but if you like, you can use $wgLoadBalancer->getServerCount() > 1 to
+but if you like, you can use wfGetLB()->getServerCount() > 1 to
 check to see if replication is in use.
 
 === Lag ===
@@ -98,14 +100,14 @@ regularly lag by several minutes, making review of recent edits
 difficult.
 
 In addition to this, MediaWiki attempts to ensure that the user sees
-events occuring on the wiki in chronological order. A few seconds of lag
+events occurring on the wiki in chronological order. A few seconds of lag
 can be tolerated, as long as the user sees a consistent picture from
 subsequent requests. This is done by saving the master binlog position
 in the session, and then at the start of each request, waiting for the
 slave to catch up to that position before doing any reads from it. If
 this wait times out, reads are allowed anyway, but the request is
 considered to be in "lagged slave mode". Lagged slave mode can be
-checked by calling $wgLoadBalancer->getLaggedSlaveMode(). The only
+checked by calling wfGetLB()->getLaggedSlaveMode(). The only
 practical consequence at present is a warning displayed in the page
 footer.
 
@@ -144,21 +146,16 @@ to avoid long-lasting locks. By default, MediaWiki opens a transaction
 at the first query, and commits it before the output is sent. Locks will
 be held from the time when the query is done until the commit. So you
 can reduce lock time by doing as much processing as possible before you
-do your write queries. Update operations which do not require database
-access can be delayed until after the commit by adding an object to
-$wgPostCommitUpdateList.
+do your write queries.
 
 Often this approach is not good enough, and it becomes necessary to
 enclose small groups of queries in their own transaction. Use the
 following syntax:
 
-$dbw =& wfGetDB( DB_MASTER );
-$dbw->immediateBegin();
+$dbw = wfGetDB( DB_MASTER );
+$dbw->begin();
 /* Do queries */
-$dbw->immediateCommit();
-
-There are functions called begin() and commit() but they don't do what
-you would expect. Don't use them.
+$dbw->commit();
 
 Use of locking reads (e.g. the FOR UPDATE clause) is not advised. They
 are poorly implemented in InnoDB and will cause regular deadlock errors.
@@ -172,3 +169,31 @@ queries, by using an appropriate condition in the WHERE clause of an
 UPDATE, or by using unique indexes in combination with INSERT IGNORE.
 Then use the affected row count to see if the query succeeded.
 
+------------------------------------------------------------------------
+    Supported DBMSs
+------------------------------------------------------------------------
+
+MediaWiki is written primarily for use with MySQL. Queries are optimized
+for it and its schema is considered the canonical version. However,
+MediaWiki does support the following other DBMSs to varying degrees.
+
+* PostgreSQL
+* SQLite
+* Oracle
+* IBM DB2
+* MSSQL
+
+More information can be found about each of these databases (known issues,
+level of support, extra configuration) in the "databases" subdirectory in
+this folder.
+
+------------------------------------------------------------------------
+    Use of GROUP BY
+------------------------------------------------------------------------
+
+MySQL supports GROUP BY without checking anything in the SELECT clause. 
+Other DBMSs (especially Postgres) are stricter and require that all the 
+non-aggregate items in the SELECT clause appear in the GROUP BY. For 
+this reason, it is highly discouraged to use SELECT * with GROUP BY 
+queries.
+