Aaron Schulz has uploaded a new change for review.
https://gerrit.wikimedia.org/r/97457
Change subject: More file backend docs
......................................................................
More file backend docs
Change-Id: Ic81e298baa7cb21d0e494e6e2ed749e7f401f2b5
---
M includes/filebackend/FileBackend.php
1 file changed, 25 insertions(+), 2 deletions(-)
git pull ssh://gerrit.wikimedia.org:29418/mediawiki/core
refs/changes/57/97457/1
diff --git a/includes/filebackend/FileBackend.php
b/includes/filebackend/FileBackend.php
index d042dc4..a6eda18 100644
--- a/includes/filebackend/FileBackend.php
+++ b/includes/filebackend/FileBackend.php
@@ -47,11 +47,34 @@
* For legacy reasons, the FSFileBackend class allows manually setting the
paths of
* containers to ones that do not respect the "wiki ID".
*
- * In key/value stores, the container is the only hierarchy (the rest is
emulated).
+ * In key/value (object) stores, containers are the only hierarchy (the rest
is emulated).
* FS-based backends are somewhat more restrictive due to the existence of real
* directory files; a regular file cannot have the same name as a directory.
Other
* backends with virtual directories may not have this limitation. Callers
should
* store files in such a way that no files and directories are under the same
path.
+ *
+ * In general, this class allows for callers to access storage through the same
+ * interface, without regard to the underlying storage system. However,
calling code
+ * must follow certain patterns and be aware of certain things to ensure
compatibility:
+ * - a) Always call prepare() on the parent directory before trying to put a
file there;
+ * key/value stores only need the container to exist first, but
filesystems need
+ * all the parent directories to exist first (prepare() is aware of all
this)
+ * - b) Always call clean() on a directory when it might become empty to
avoid empty
+ * directory buildup on filesystems; key/value stores never have empty
directories,
+ * so doing this helps preserve consistency in both cases
+ * - c) Likewise, do not rely on the existence of empty directories for
anything;
+ * calling directoryExists() on a path that prepare() was previously
called on
+ * will return false for key/value stores if there are no files under
that path
+ * - d) Never alter the resulting FSFile returned from getLocalReference(),
as it could
+ * either be a copy of the source file in /tmp or the original source
file itself
+ * - e) Use a file layout that results in never attempting to store files
over directories
+ * or directories over files; key/value stores allow this but
filesystems do not
+ * - f) Use ASCII file names (e.g. base32, IDs, hashes) to avoid Unicode
issues in Windows
+ * - g) Do not assume that move operations are atomic (difficult with
key/value stores)
+ * - h) Do not assume that file stat or read operations always have
immediate consistency;
+ * various methods have a "latest" flag that should always be used if
up-to-date
+ * information is required (this trades performance for correctness as
needed)
+ * - i) Do not assume that directory listings have immediate consistency
*
* Methods of subclasses should avoid throwing exceptions at all costs.
* As a corollary, external dependencies should be kept to a minimum.
@@ -60,7 +83,7 @@
* @since 1.19
*/
abstract class FileBackend {
- /** @var string Unique backend name */
+ /** @var string Unique backend name */
protected $name;
/** @var string Unique wiki name */
--
To view, visit https://gerrit.wikimedia.org/r/97457
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: newchange
Gerrit-Change-Id: Ic81e298baa7cb21d0e494e6e2ed749e7f401f2b5
Gerrit-PatchSet: 1
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Aaron Schulz <[email protected]>
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