Hello Kudu Jenkins, Adar Dembo,
I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/10340
to look at the new patch set (#6).
Change subject: KUDU-2359: allow startup with missing data dirs
......................................................................
KUDU-2359: allow startup with missing data dirs
Context
-------
As a part of previous disk failure work, Kudu currently supports opening
the FS layout in the face of EIO, EROFS, etc. POSIX codes when reading
FS and block manager instance files. The directory manager, in such
cases, labels the data directory in which the bad file resides as failed
in memory. The check that enforces consistency between path instance
metadata files (PIMFs) accounts for such failed directories.
Separately, the introduction of the `kudu fs update_dirs` tool expanded
the logic used to open the FS layout to serve two additional purposes
when running the tool:
- To open the FS layout as the user specified it on a best-effort basis,
ignoring any inconsistencies across PIMFs. This mode allows Kudu to
stage the requested FS layout and test whether existing tablets would
break under the given layout.
- To actually update the FS layout on disk to match the user input.
Walking down the FS-layout-opening path in this mode, Kudu will
create any missing files or directories it encounters along the way.
In this mode, the PIMF consistency check is performed after updating
the appropriate instance files.
The above behavior is currently encapsulated in FsManager::Open() and
the consequent call to DataDirManager::Open().
As mentioned in the JIRA, not accounted for by this previous work, a
disk failure can present itself as a failure to read directory entries
(POSIX code ENOENT), leading to NotFound errors. Therein lies some
conflict in the above logic:
- when opening the FS layout normally (i.e. not running the update tool)
and a NotFound error is encountered (e.g. the user asks for
--fs_data_dirs=/a,/b but only /a can be found), it would be desirable
to treat the affected directory how we currently treat failed
directories
- however, when updating directories, NotFound statuses are still meant
to indicate missing directories to be created.
The questions then become, "How should we treat ENOENT/NotFound errors?
Should they be different than disk failures? If so, how?" There are a
couple options to consider:
1. Lump ENOENT in with the list of POSIX codes that signify a disk
error. This change would mean that semantically, a failed directory
is no different than a missing one, and all of the above mentioned
codepaths must be updated to account for this. Additionally, this
would affect all other codepaths that may yield ENOENT -- codepaths
that previously triggered disk failure handling would trigger that
handling for ENOENT errors.
2. Treat NotFound errors as a special case during update/open only. When
reading FS or block manager instance files, extend disk error
checking to also check for NotFound errors, and treat the errors
similarly, creating in-memory "unhealthy" instances. To open the FS
normally, these unhealthy instances will simply correspond to failed
directories. To update the FS layout, we can leverage the fact that
the FS update tool doesn't support running with any failed
directories, attempting to create all directories and files for _all_
unhealthy instances (both missing and failed) will correctly yield
success in the face of only missing directories and failure in the
presence of any failed directory.
This patch implements Option 2 instead of Option 1. ENOENT is still a
file-specific code, and so lumping it in to trigger DataDir-wide error
handling, even if it may be indicative of disk-wide failure, seems
inappropriate. It could also be argued that if NotFound errors are
discovered at server runtime (e.g. because some malicious user is
deleting files left and right), maybe the best course of action wouldn't
be to treat the directory as failed, but to crash Kudu altogether.
Notes on the new stuff
----------------------
The newly supported scenario is different than starting up Kudu with
extra or missing entries in `fs_data_dirs`, which is still not supported
unless running the update tool.
Examples:
- If an existing server were configured with --fs_data_dirs=/a,/b,/c,
and it were restarted such that only /a,/b existed on disk, Kudu will
start up and list /a,/b,/c, and note that /c is failed.
- If the above server were restarted with --fs_data_dirs=/a,/b, even if
only /a,/b existed on disk, Kudu would fail to start up until running
`kudu fs update_dirs <other flags> --fs_data_dirs=/a,/b`
Some changes in this patch include:
- methods involved in loading PIMFs now treat missing instance files as
"unhealthy", the same way they treat files that fail due to disk
errors
- DataDirManager::LoadInstances() has been updated to treat missing
PIMFs as "unhealthy", the same way they treat PIMFs that yield disk
errors, returning the successfully loaded, "unhealthy" instances
- a side effect of this is that all user-specified data dirs will have
in-memory DataDirs created for them, even if they don't exist on disk
- various codepaths that previously ended FsManager::Open() with an
IOError/Corruption because all drives were failed will now return
NotFound, indicating Kudu should attempt to create a new FS layout.
This means that a server that has lost all of its data dirs to disk
failures is semantically equivalent to a brand new server; Kudu will
attempt to create a new FS layout in these cases
- as a byproduct of the above changes, when opening the FS layout in
ENFORCE_CONSISTENCY mode with an extra entry in `fs_data_dirs`, Kudu
will fail later than before, at the integrity check, and yield an
IOError instead of a NotFound error
- the UUID and UUID index assignment for missing directories has been
updated when opening the speculative directory manager; see
DataDirManager::Open() for more details.
Change-Id: I61a71265c3cc34a7b72320149770a814ec7f8351
---
M src/kudu/fs/block_manager_util.cc
M src/kudu/fs/data_dirs-test.cc
M src/kudu/fs/data_dirs.cc
M src/kudu/fs/data_dirs.h
M src/kudu/fs/fs_manager-test.cc
M src/kudu/fs/fs_manager.cc
M src/kudu/tools/kudu-tool-test.cc
7 files changed, 268 insertions(+), 143 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/40/10340/6
--
To view, visit http://gerrit.cloudera.org:8080/10340
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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I61a71265c3cc34a7b72320149770a814ec7f8351
Gerrit-Change-Number: 10340
Gerrit-PatchSet: 6
Gerrit-Owner: Andrew Wong <[email protected]>
Gerrit-Reviewer: Adar Dembo <[email protected]>
Gerrit-Reviewer: Andrew Wong <[email protected]>
Gerrit-Reviewer: Kudu Jenkins
