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editor: fix edge case with in memory file-store size limit
There are a few cases where we will set a single file into to the
editor's FileStore object more than once. Notably, for copied and
then modified files, we will set it at least twice. Three times if
editing fails (which it can for symlinks).
If we pass the in-memory storage limit in between the first (or second
if editing fails) time we set the file and the last time we set the
file, we will write the data to the in memory store the first time and
the file store the last time. We didn't remove it form the in-memory
store though, and we always prefer reading from the in-memory store.
This means we can sometimes end up with the wrong version of a file.
This is fairly unlikely to happen in normal use since you need to hit
the memory limit between two writes to the store for the same file.
We only write a file multiple times if a) the file (and not one of
it's parent directories) is copied and then modified or b) editing
fails. From what I can tell, it's only common for editing to fail for
symlinks, and they ten to be relatively small data that is unlikely to
push over the limit. Finally, the default limit is 100MB which I
would expect to be most often either well over (source code) or well
under (binaries or automated changes) the size of the changes files in
a single commit.
The easiest way to reproduce this is to set the in-memory cache size
to 0 and then commit a copied and modified symlink. The empty-string
version from the failed editing will be the one that persists. I
happened to stumble upon this while trying (and failing) to test a
bug-fix for a related bug with identical symptoms (empty simlink). I
have seen this in the wild, once, but couldn't reproduce it at the
time. The repo in question is quite large and quite active, so I am
quite confident in my estimation that this is a real, but very rare,
problem.
The test changes attached to this was mneant to test a related bug,
but turned out not to actually cover the bug in question. They did
trigger this bug though, and are worthwhile to test, so I kept them.
| author | David Schleimer <dschleimer@fb.com> |
|---|---|
| date | Mon, 07 Apr 2014 17:51:59 -0700 |
| parents | 9c3b4f59e7e6 |
| children |
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SVN-fs-dump-format-version: 2 UUID: 307f02f4-2d74-44cb-98a4-4e162241d396 Revision-number: 0 Prop-content-length: 56 Content-length: 56 K 8 svn:date V 27 2012-10-06T08:50:46.559327Z PROPS-END Revision-number: 1 Prop-content-length: 105 Content-length: 105 K 10 svn:author V 7 pmezard K 8 svn:date V 27 2012-10-06T08:50:46.581582Z K 7 svn:log V 4 init PROPS-END Node-path: trunk Node-kind: dir Node-action: add Prop-content-length: 10 Content-length: 10 PROPS-END Node-path: trunk/a Node-kind: file Node-action: add Prop-content-length: 10 Text-content-length: 2 Text-content-md5: 60b725f10c9c85c70d97880dfe8191b3 Text-content-sha1: 3f786850e387550fdab836ed7e6dc881de23001b Content-length: 12 PROPS-END a Node-path: trunk/dir Node-kind: dir Node-action: add Prop-content-length: 10 Content-length: 10 PROPS-END Node-path: trunk/dir/b Node-kind: file Node-action: add Prop-content-length: 10 Text-content-length: 2 Text-content-md5: 3b5d5c3712955042212316173ccf37be Text-content-sha1: 89e6c98d92887913cadf06b2adb97f26cde4849b Content-length: 12 PROPS-END b Revision-number: 2 Prop-content-length: 113 Content-length: 113 K 10 svn:author V 7 pmezard K 8 svn:date V 27 2012-10-06T08:50:47.048033Z K 7 svn:log V 11 changefiles PROPS-END Node-path: trunk/a Node-kind: file Node-action: change Text-content-length: 4 Text-content-md5: 0d227f1abf8c2932d342e9b99cc957eb Text-content-sha1: d7c8127a20a396cff08af086a1c695b0636f0c29 Content-length: 4 a a Node-path: trunk/dir/b Node-kind: file Node-action: change Text-content-length: 4 Text-content-md5: 06ac26ed8b614fc0b141e4542aa067c2 Text-content-sha1: f6980469e74f7125178e88ec571e06fe6ce86e95 Content-length: 4 b b Revision-number: 3 Prop-content-length: 107 Content-length: 107 K 10 svn:author V 7 pmezard K 8 svn:date V 27 2012-10-06T08:50:50.058224Z K 7 svn:log V 6 revert PROPS-END Node-path: trunk Node-kind: dir Node-action: delete Node-path: trunk Node-kind: dir Node-action: add Node-copyfrom-rev: 1 Node-copyfrom-path: trunk Revision-number: 4 Prop-content-length: 108 Content-length: 108 K 10 svn:author V 7 pmezard K 8 svn:date V 27 2012-10-06T08:50:54.047396Z K 7 svn:log V 7 revert2 PROPS-END Node-path: trunk/a Node-kind: file Node-action: delete Node-path: trunk/a Node-kind: file Node-action: add Node-copyfrom-rev: 2 Node-copyfrom-path: trunk/a Text-copy-source-md5: 0d227f1abf8c2932d342e9b99cc957eb Text-copy-source-sha1: d7c8127a20a396cff08af086a1c695b0636f0c29 Node-path: trunk/dir/b Node-kind: file Node-action: delete Node-path: trunk/dir/b Node-kind: file Node-action: add Node-copyfrom-rev: 2 Node-copyfrom-path: trunk/dir/b Text-copy-source-md5: 06ac26ed8b614fc0b141e4542aa067c2 Text-copy-source-sha1: f6980469e74f7125178e88ec571e06fe6ce86e95