docs: Convert logger.txt and linkcache.txt to Markdown

Indexing on doc.wikimedia.org doesn't work for .txt files.
This was done for Google Code-In 2019.

Bug: T233244
Change-Id: I4c441f92b89c1ab1053c5f16a6e7100f2e5e9492

1 files changed, 24 insertions, 0 deletions

diff --git a/docs/LinkCache.md b/docs/LinkCache.md
new file mode 100644
index 000000000000..841354a80afb
--- /dev/null
+++ b/docs/LinkCache.md
@@ -0,0 +1,24 @@
+The LinkCache class maintains a list of article titles and the information about
+whether or not the article exists in the database. This is used to mark up links
+when displaying a page. If the same link appears more than once on any page,
+then it only has to be looked up once. In most cases, link lookups are done in
+batches with the LinkBatch class, or the equivalent in Parser::replaceLinkHolders(),
+so the link cache is mostly useful for short snippets of parsed text (such as
+the site notice), and for links in the navigation areas of the skin.
+
+The link cache was formerly used to track links used in a document for the
+purposes of updating the link tables. This application is now deprecated.
+
+To create a batch, you can use the following code:
+
+~~~{.php}
+$pages = [ 'Main Page', 'Project:Help', /* ... */ ];
+$titles = [];
+
+foreach( $pages as $page ){
+	$titles[] = Title::newFromText( $page );
+}
+
+$batch = new LinkBatch( $titles );
+$batch->execute();
+~~~