Matthias Sohn [Thu, 30 Mar 2023 11:43:17 +0000 (13:43 +0200)]
Prevent infinite loop rescanning the pack list on PackMismatchException
We found, when analysing an incident where Gerrit's gc runner thread got
stuck, that we can end up in an infinite loop in
ObjectDirectory#openPackedObject which tries to rescan the pack
list and starts over trying to open a packed object in an unconfined
loop if it catches a PackMismatchException.
Here the relevant part of a thread dump we created while the gc runner
was stuck:
"WorkQueue-2[java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask@350812a3[Not
completed,
task = java.util.concurrent.Executors$RunnableAdapter@5425d7ee]]" #72
tid=0x00007f73cee1c800 nid=0x584
runnable [0x00007f7392d57000]
java.lang.Thread.State: RUNNABLE
at org.eclipse.jgit.internal.storage.file.WindowCache.removeAll(WindowCache.java:716)
at org.eclipse.jgit.internal.storage.file.WindowCache.purge(WindowCache.java:399)
at org.eclipse.jgit.internal.storage.file.PackFile.close(PackFile.java:296)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.reuseMap(ObjectDirectory.java:973)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.scanPacksImpl(ObjectDirectory.java:904)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.scanPacks(ObjectDirectory.java:895)
- locked <0x000000050a498f60> (a
java.util.concurrent.atomic.AtomicReference)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.searchPacksAgain(ObjectDirectory.java:794)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.openPackedObject(ObjectDirectory.java:465)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.openPackedFromSelfOrAlternate(ObjectDirectory.java:417)
at org.eclipse.jgit.internal.storage.file.ObjectDirectory.openObject(ObjectDirectory.java:408)
at org.eclipse.jgit.internal.storage.file.WindowCursor.open(WindowCursor.java:132)
at org.eclipse.jgit.lib.ObjectReader$1.open(ObjectReader.java:279)
at org.eclipse.jgit.revwalk.RevWalk$2.next(RevWalk.java:1031)
at org.eclipse.jgit.internal.storage.pack.PackWriter.findObjectsToPack(PackWriter.java:1911)
at org.eclipse.jgit.internal.storage.pack.PackWriter.preparePack(PackWriter.java:960)
at org.eclipse.jgit.internal.storage.pack.PackWriter.preparePack(PackWriter.java:876)
at org.eclipse.jgit.internal.storage.file.GC.writePack(GC.java:1168)
at org.eclipse.jgit.internal.storage.file.GC.repack(GC.java:852)
at org.eclipse.jgit.internal.storage.file.GC.doGc(GC.java:269)
at org.eclipse.jgit.internal.storage.file.GC.gc(GC.java:220)
at org.eclipse.jgit.api.GarbageCollectCommand.call(GarbageCollectCommand.java:179)
at com.google.gerrit.server.git.GarbageCollection.run(GarbageCollection.java:112)
at com.google.gerrit.server.git.GarbageCollection.run(GarbageCollection.java:75)
at com.google.gerrit.server.git.GarbageCollection.run(GarbageCollection.java:71)
at com.google.gerrit.server.git.GarbageCollectionRunner.run(GarbageCollectionRunner.java:76)
at com.google.gerrit.server.logging.LoggingContextAwareRunnable.run(LoggingContextAwareRunnable.java:103)
at java.util.concurrent.Executors$RunnableAdapter.call(java.base@11.0.18/Executors.java:515)
at java.util.concurrent.FutureTask.runAndReset(java.base@11.0.18/FutureTask.java:305)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(java.base@11.0.18/ScheduledThreadPoolExecutor.java:305)
at com.google.gerrit.server.git.WorkQueue$Task.run(WorkQueue.java:612)
at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@11.0.18/ThreadPoolExecutor.java:1128)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@11.0.18/ThreadPoolExecutor.java:628)
at java.lang.Thread.run(java.base@11.0.18/Thread.java:829)
The code in ObjectDirectory#openPackedObject [1] apparently assumes that
this is caused by a transient problem which it can resume from by
retrying. We use `core.trustFolderStat = false` on this server since it
uses NFS. The incident we had showed that we can enter into an infinite
loop here if there is a permanent mismatch between a pack file and its
corresponding pack index. I am not yet sure how this can happen.
Break the infinite loop by limiting the number of attempts rescanning
the pack list to 5 retries. When we exceed this threshold set the type
of the PackMismatchException to permanent and rethrow it which breaks
the infinite loop.
Also apply the same limit in #getPackedObjectSize
and #selectObjectRepresentation where we use similar retry loops.
Saša Živkov [Fri, 3 Jun 2022 14:36:43 +0000 (16:36 +0200)]
Fix connection leak for smart http connections
SmartHttpPushConnection: close InputStream and OutputStream after
processing. Wrap IOExceptions which aren't TransportExceptions already
as a TransportException.
Also-By: Matthias Sohn <matthias.sohn@sap.com>
Change-Id: I8e11d899672fc470c390a455dc86367e92ef9076
Matthias Sohn [Fri, 3 Dec 2021 21:45:05 +0000 (22:45 +0100)]
Update maven plugins
- build-helper-maven-plugin to 3.2.0
- jacoco-maven-plugin to 0.8.7
- maven-antrun-plugin to 3.0.0
- maven-dependency-plugin to 3.2.0
- maven-enforcer-plugin to 3.0.0
- maven-jar-plugin to 3.2.0
- maven-javadoc-plugin to 3.3.1
- maven-jxr-plugin to 3.1.1
- maven-pmd-plugin to 3.15.0
- maven-project-info-reports-plugin to 3.1.2
- maven-resources-plugin to 3.2.0
- maven-shade-plugin to 3.2.4
- maven-site-plugin to 3.9.1
- maven-source-plugin to 3.2.1
- maven-surefire-plugin to 3.0.0-M5
- spotbugs-maven-plugin to 4.3.0
- tycho and tycho-extras to 1.7.0
RefDirectory.scanRef: Re-use file existence check done in snapshot creation
Return immediately in scanRef if the loose ref was identified as
missing when a snapshot was attempted for the ref. This will help
performance of scanRef when the ref is packed but has a corresponding
empty dir in 'refs/'.
For example, consider the case where we create 50k sharded refs in
a new namespace called 'new-refs' using an atomic 'BatchRefUpdate'.
The refs are named like 'refs/new-refs/01/1/1', 'refs/new-refs/01/1/2',
'refs/new-refs/01/1/3' and so on. After the refs are created, the
'new-refs' namespace looks like below:
$ find refs/new-refs -type f | wc -l
0
$ find refs/new-refs -type d | wc -l
5101
At this point, an 'exactRef' call on each of the 50k refs without
this change takes ~2.5s, where as with this change it takes ~1.5s.
FileSnapshot: Lazy load file store attributes cache
Doing a getFileStoreAttributes call even when the file doesn't
exist is unnecessary. This call is particularly slow on some
filesystems. Instead, do it only when the file exists and load
the appropriate cache.
This update can help speed up RefDirectory.exactRef when the ref
is packed, but has a corresponding empty dir for it under 'refs/'.
This scenario can happen when an atomic 'BatchRefUpdate' creates
new sharded refs.
For example, consider the case where we create 50k sharded refs in
a new namespace called 'new-refs' using an atomic 'BatchRefUpdate'.
The refs are named like 'refs/new-refs/01/1/1', 'refs/new-refs/01/1/2',
'refs/new-refs/01/1/3' and so on. After the refs are created, the
'new-refs' namespace looks like below:
$ find refs/new-refs -type f | wc -l
0
$ find refs/new-refs -type d | wc -l
5101
At this point, an 'exactRef' call on each of the 50k refs without
this change takes ~30s, where as with this change it takes ~2.5s.
Thomas Wolf [Sun, 28 Nov 2021 10:42:20 +0000 (11:42 +0100)]
FS: debug logging only if system config file cannot be found
The command 'git config --system --show-origin --list -z' fails if
the system config doesn't exist. Use debug logging instead of a
warning for failures of that command. Typically the user cannot do
anything about it anyway, and JGit will just work without system
config.
Bug: 577492
Change-Id: If628ab376182183aea57a385c169e144d371bbb2 Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
Thomas Wolf [Fri, 19 Nov 2021 18:15:46 +0000 (19:15 +0100)]
Better git system config finding
We've used "GIT_EDITOR=edit git config --system --edit" to determine
the location of the git system config for a long time. But git 2.34.0
always expects this command to have a tty, but there isn't one when
called from Java. If there isn't one, the Java process may get a
SIGTTOU from the child process and hangs.
Arguably it's a bug in C git 2.34.0 to unconditionally assume there
was a tty. But JGit needs a fix *now*, otherwise any application using
JGit will lock up if git 2.34.0 is installed on the machine.
Therefore, use a different approach if the C git found is 2.8.0 or
newer: parse the output of
git config --system --show-origin --list -z
"--show-origin" exists since git 2.8.0; it prefixes the values with
the file name of the config file they come from, which is the system
config file for this command. (This works even if the first item in
the system config is an include.)
Bug: 577358
Change-Id: I3ef170ed3f488f63c3501468303119319b03575d Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
(cherry picked from commit 9446e62733da5005be1d5182f0dce759a3052d4a)
Matthias Sohn [Fri, 15 Oct 2021 20:32:00 +0000 (22:32 +0200)]
Merge branch 'stable-5.9' into stable-5.10
* stable-5.9:
Fix missing peel-part in lsRefsV2 for loose annotated tags
reftable: drop code for truncated reads
reftable: pass on invalid object ID in conversion
Update eclipse-jarsigner-plugin to 1.3.2
Fix running benchmarks from bazel
Update eclipse-jarsigner-plugin to 1.3.2
Unfortunately, the existing UploadPackTest didn't reveal this issue
although it provided the test case needed to do so: testV2LsRefsPeel.
This is because The UploadPackTest uses InMemoryRepository which
internally uses Dfs* implementations. The issue is only reproducible
when using the FileRepository.
It is a non-trivial task to refactor the UploadPackTest to work against
both InMemoryRepository and FileRepository and this change is not trying
to do that. This change creates a new test:
UploadPackLsRefsFileRepositoryTest and copies the necesssary code from
the UploadPackTest.
The reftable format is a block based format, but allows for variably
sized blocks. This obviously happens for reflog blocks (which are zlib
compressed), but is also accepted for index blocks: In the spec, this
is motivated as
To achieve constant O(1) disk seeks for lookups the index must be
a single level, which is permitted to exceed the file's
configured block size, but not the format's max block size of
15.99 MiB.
Hence, when parsing a block, one cannot be sure of its exact size:
after reading a default-size block (eg. 4kb), the block header may
state that the block is in fact larger.
Before, the code would mark the block as `truncated`, noting
// Its OK during sequential scan for an index block to have been
// partially read and be truncated in-memory. This happens when
// the index block is larger than the file's blockSize. Caller
// will break out of its scan loop once it sees the blockType.
This looks like either
* a remnant of never-implemented functionality. There is no reason to
ever sequentially scan an index block.
* alluding to sequential scan of the data blocks before the index
blocks (eg. scanning refs, which ends when we find the first ref index
block, and we can then ignore the index block).
This comment is followed by code that populates the
restartTbl/restartCnt fields relative to the (possibly truncated)
buffer. If the buffer is truncated, this essentially reads garbage,
leading to OOB array access when using the index block.
Fix this by dropping the truncated logic and issuing a second read if
the first read was short.
Add a test.
We have never observed this failure scenario at Google. We use 64kb
blocksize, which requires us to need fewer index entries. The reftable
spec mentions an Android repo of size 36M. With 64kb blocks, that's
just 562 index entries. Even with historical growth, we are long from
requiring an index whose size exceeds a single block.
When adding the analogous test for seeking refs, there was no failure.
This points to another possibility which is that the code tries to
avoid writing large index blocks for refs.
Antonio Barone [Wed, 1 Sep 2021 10:04:07 +0000 (12:04 +0200)]
GitServlet: allow to override default error handlers
GitServlet delegates repository access over HTTP to the GitFilter
servlet.
GitServlet, in turn, can be extended by jgit consumers to provide custom
logic when handling such operations.
This is the case, for example, with Gerrit Code Review, which provides
custom behavior with a GitOverHttpServlet [1].
Among possible customizations, the ability of specifying a custom error
handler for UploadPack and ReceivePack was already introduced in
GitFilter by Idd3b87d6b and I9c708aa5a2, respectively.
However the `setUploadPackErrorHandler` and `setReceivePackErrorHandler`
methods were never added to the GitServlet.
Expose the `setUploadPackErrorHandler` and `setReceivePackErrorHandler`
methods to the GitServlet, so that consumers of the jgit library might
specify custom error handlers.
Thomas Wolf [Sun, 25 Jul 2021 13:44:35 +0000 (15:44 +0200)]
[test] Create keystore with the keytool of the running JDK
Call keytool with the absolute path of "java.home". Otherwise a keytool
for a different, maybe even newer Java version might be picked up, and
then the keystore may not be readable by the JVM used to run the tests.
Antonio Barone [Wed, 2 Jun 2021 15:13:17 +0000 (18:13 +0300)]
Retry loose object read upon "Stale file handle" exception
When reading loose objects over NFS it is possible that the OS syscall
would fail with ESTALE errors: This happens when the open file
descriptor no longer refers to a valid file.
Notoriously it is possible to hit this scenario when git data is shared
among multiple clients, for example by multiple gerrit instances in HA.
If one of the two clients performs a GC operation that would cause the
packing and then the pruning of loose objects, the other client might
still hold a reference to those objects, which would cause an exception
to bubble up the stack.
The Linux NFS FAQ[1] (at point A.10), suggests that the proper way to
handle such ESTALE scenarios is to:
"[...] close the file or directory where the error occurred, and reopen
it so the NFS client can resolve the pathname again and retrieve the new
file handle."
In case of a stale file handle exception, we now attempt to read the
loose object again (up to 5 times), until we either succeed or encounter
a FileNotFoundException, in which case the search can continue to
Packfiles and alternates.
The limit of 5 provides an arbitrary upper bounds that is consistent to
the one chosen when handling stale file handles for packed-refs
files (see [2] for context).
BatchRefUpdate: Skip saving conflicting ref names and prefixes in memory
Rather than getting all ref names and prefixes and saving them
in memory to perform the check for conflicting names, rely on
RefDirectory.isNameConflicting as it is no longer an expensive
call after it was optimized in Ie994fc.
The old optimization to save ref names and prefixes in memory
was targeted towards making clones faster. With this change,
the clone performance is unaffected when tests were done with
repos containing many(~500k) refs.
Here are few recorded elapsed times for creating 10 branches
using BatchRefUpdate on NFS based repositories with varying
loose refs count. As seen here, this change helps improve the
BatchRefUpdate performance from O(n^2) to O(1).
loose_refs_count with_change without_change
50 241 ms 310 ms
300 263 ms 1502 ms
1k 181 ms 4241 ms
2k 204 ms 6440 ms
9k 158 ms 25930 ms
20k 154 ms 60443 ms
50k 171 ms 135199 ms
110k 157 ms 329450 ms
160k 209 ms 396328 ms
This update improves the Gerrit notedb migration performance
as it uses BatchRefUpdate to write change meta refs similar to
the test performed above.
Update tests to record the number of events fired post-setup and only
assert for events fired during BatchRefUpdate.execute. For tests which
use writeLooseRef to setup refs, create new tests which assert the
number of RefsChangedEvent(s) rather than updating the existing ones
to call RefDirectory.exactRef as it changes the code path.
Avoid having to scan over ALL loose refs to determine if the
name is nested within or is a container of an existing reference.
This can get really expensive if there are too many loose refs.
Instead use exactRef and getRefsByPrefix which scan based on a
prefix.
With a simple shell script(like below) using jgit client to create
1k refs in a new repository on NFS, this change brings down the time
from 12mins to 7mins.
for ref in $(seq 1 1000); do
jgit branch "$ref"
done
Here are few recorded elapsed times to create a new branch on NFS
based repositories with varying loose refs count. As we see here,
this change improves the name conflicting check from O(n^2) to O(1).
loose_refs_count with_change without_change
50 44 ms 164 ms
300 45 ms 1193 ms
1k 38 ms 2610 ms
2k 44 ms 6003 ms
9k 46 ms 27860 ms
20k 45 ms 48591 ms
50k 51 ms 135471 ms
110k 43 ms 294252 ms
160k 52 ms 430976 ms
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