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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 | f28e0f54a6ef |
| children |
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SVN-fs-dump-format-version: 2 UUID: 764a21f0-1c44-4bc9-b81b-0321cc58934d Revision-number: 0 Prop-content-length: 56 Content-length: 56 K 8 svn:date V 27 2011-05-24T15:46:13.951233Z PROPS-END Revision-number: 1 Prop-content-length: 114 Content-length: 114 K 7 svn:log V 14 Initial commit K 10 svn:author V 5 augie K 8 svn:date V 27 2011-05-24T15:46:14.518711Z PROPS-END Node-path: branches Node-kind: dir Node-action: add Prop-content-length: 10 Content-length: 10 PROPS-END Node-path: tags Node-kind: dir Node-action: add Prop-content-length: 10 Content-length: 10 PROPS-END Node-path: trunk Node-kind: dir Node-action: add Prop-content-length: 10 Content-length: 10 PROPS-END Revision-number: 2 Prop-content-length: 111 Content-length: 111 K 7 svn:log V 11 Added fileA K 10 svn:author V 5 augie K 8 svn:date V 27 2011-05-24T15:46:14.922304Z PROPS-END Node-path: trunk/fileA Node-kind: file Node-action: add Prop-content-length: 10 Text-content-length: 6 Text-content-md5: 017715e60b9a9450d604e0d489ebc83a Text-content-sha1: d0bcb0015aaadb5317419294648c8da6714af81f Content-length: 16 PROPS-END fileA Revision-number: 3 Prop-content-length: 112 Content-length: 112 K 7 svn:log V 12 added branch K 10 svn:author V 5 augie K 8 svn:date V 27 2011-05-24T15:46:15.328642Z PROPS-END Node-path: branches/A Node-kind: dir Node-action: add Node-copyfrom-rev: 1 Node-copyfrom-path: trunk Node-path: branches/A/fileA Node-kind: file Node-action: add Node-copyfrom-rev: 2 Node-copyfrom-path: trunk/fileA Text-copy-source-md5: 017715e60b9a9450d604e0d489ebc83a Text-copy-source-sha1: d0bcb0015aaadb5317419294648c8da6714af81f Revision-number: 4 Prop-content-length: 111 Content-length: 111 K 7 svn:log V 11 Added fileB K 10 svn:author V 5 augie K 8 svn:date V 27 2011-05-24T15:46:15.616098Z PROPS-END Node-path: trunk/fileB Node-kind: file Node-action: add Prop-content-length: 10 Text-content-length: 6 Text-content-md5: 4eb63bbdec5dfa425e3735dc1d4c5ee8 Text-content-sha1: 03939175ceac92b9c6464d037a0243e22563c423 Content-length: 16 PROPS-END fileB Revision-number: 5 Prop-content-length: 113 Content-length: 113 K 7 svn:log V 13 added bad tag K 10 svn:author V 5 augie K 8 svn:date V 27 2011-05-24T15:46:16.057440Z PROPS-END Node-path: tags/A Node-kind: dir Node-action: add Node-copyfrom-rev: 1 Node-copyfrom-path: trunk Node-path: tags/A/fileA Node-kind: file Node-action: add Node-copyfrom-rev: 2 Node-copyfrom-path: trunk/fileA Text-copy-source-md5: 017715e60b9a9450d604e0d489ebc83a Text-copy-source-sha1: d0bcb0015aaadb5317419294648c8da6714af81f Node-path: tags/A/fileB Node-kind: file Node-action: add Node-copyfrom-rev: 4 Node-copyfrom-path: trunk/fileB Text-copy-source-md5: 4eb63bbdec5dfa425e3735dc1d4c5ee8 Text-copy-source-sha1: 03939175ceac92b9c6464d037a0243e22563c423