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Fix race condition causing double deletion of ssts

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Summary:
Possible interleaved execution of background compaction thread calling `FindObsoleteFiles (no full scan) / PurgeObsoleteFiles` and user thread calling `FindObsoleteFiles (full scan) / PurgeObsoleteFiles` can lead to race condition on which RocksDB attempts to delete a file twice. The second attempt will fail and return `IO error`. This may occur to other files,  but this PR targets sst.
Also add a unit test to verify that this PR fixes the issue.

The newly added unit test `obsolete_files_test` has a test case for this scenario, implemented in `ObsoleteFilesTest#RaceForObsoleteFileDeletion`. `TestSyncPoint`s are used to coordinate the interleaving the `user_thread` and background compaction thread. They execute as follows
```
timeline              user_thread                background_compaction thread
t1   |                                          FindObsoleteFiles(full_scan=false)
t2   |     FindObsoleteFiles(full_scan=true)
t3   |                                          PurgeObsoleteFiles
t4   |     PurgeObsoleteFiles
     V
```
When `user_thread` invokes `FindObsoleteFiles` with full scan, it collects ALL files in RocksDB directory, including the ones that background compaction thread have collected in its job context. Then `user_thread` will see an IO error when trying to delete these files in `PurgeObsoleteFiles` because background compaction thread has already deleted the file in `PurgeObsoleteFiles`.
To fix this, we make RocksDB remember which (SST) files have been found by threads after calling `FindObsoleteFiles` (see `DBImpl#files_grabbed_for_purge_`). Therefore, when another thread calls `FindObsoleteFiles` with full scan, it will not collect such files.

ajkr could you take a look and comment? Thanks!
Closes https://github.com/facebook/rocksdb/pull/3638

Differential Revision: D7384372

Pulled By: riversand963

fbshipit-source-id: 01489516d60012e722ee65a80e1449e589ce26d3
This commit is contained in:
Yanqin Jin 2018-03-28 10:23:31 -07:00 committed by Facebook Github Bot
parent 90c542347a
commit 1f5def1653
9 changed files with 317 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
CMakeLists.txt
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@ -833,6 +833,7 @@ if(WITH_TESTS)
db/db_write_test.cc
db/dbformat_test.cc
db/deletefile_test.cc
db/obsolete_files_test.cc
db/external_sst_file_basic_test.cc
db/external_sst_file_test.cc
db/fault_injection_test.cc

4
Makefile
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@ -474,6 +474,7 @@ TESTS = \
write_batch_with_index_test \
write_controller_test\
deletefile_test \
obsolete_files_test \
table_test \
geodb_test \
delete_scheduler_test \
@ -1380,6 +1381,9 @@ options_file_test: db/options_file_test.o $(LIBOBJECTS) $(TESTHARNESS)
deletefile_test: db/deletefile_test.o $(LIBOBJECTS) $(TESTHARNESS)
$(AM_LINK)
obsolete_files_test: db/obsolete_files_test.o $(LIBOBJECTS) $(TESTHARNESS)
$(AM_LINK)
geodb_test: utilities/geodb/geodb_test.o $(LIBOBJECTS) $(TESTHARNESS)
$(AM_LINK)

5
TARGETS
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@ -655,6 +655,11 @@ ROCKS_TESTS = [
"utilities/document/document_db_test.cc",
"serial",
],
[
"obsolete_files_test",
"db/obsolete_files_test.cc",
"serial",
],
[
"dynamic_bloom_test",
"util/dynamic_bloom_test.cc",

2
db/db_impl.cc
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@ -300,6 +300,8 @@ Status DBImpl::CloseHelper() {
TEST_SYNC_POINT("DBImpl::~DBImpl:WaitJob");
bg_cv_.Wait();
}
TEST_SYNC_POINT_CALLBACK("DBImpl::CloseHelper:PendingPurgeFinished",
&files_grabbed_for_purge_);
EraseThreadStatusDbInfo();
flush_scheduler_.Clear();

7
db/db_impl.h
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@ -1186,6 +1186,10 @@ class DBImpl : public DB {
// A queue to store filenames of the files to be purged
std::deque<PurgeFileInfo> purge_queue_;
// A vector to store the file numbers that have been assigned to certain
// JobContext. Current implementation tracks ssts only.
std::vector<uint64_t> files_grabbed_for_purge_;
// A queue to store log writers to close
std::deque<log::Writer*> logs_to_free_queue_;
int unscheduled_flushes_;
@ -1389,6 +1393,9 @@ class DBImpl : public DB {
bool HaveManualCompaction(ColumnFamilyData* cfd);
bool MCOverlap(ManualCompactionState* m, ManualCompactionState* m1);
bool ShouldPurge(uint64_t file_number) const;
void MarkAsGrabbedForPurge(uint64_t file_number);
size_t GetWalPreallocateBlockSize(uint64_t write_buffer_size) const;
Env::WriteLifeTimeHint CalculateWALWriteHint() {
return Env::WLTH_SHORT;

33
db/db_impl_compaction_flush.cc
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@ -1479,6 +1479,7 @@ void DBImpl::BackgroundCallCompaction(PrepickedCompaction* prepicked_compaction,
// have created (they might not be all recorded in job_context in case of a
// failure). Thus, we force full scan in FindObsoleteFiles()
FindObsoleteFiles(&job_context, !s.ok() && !s.IsShutdownInProgress());
TEST_SYNC_POINT("DBImpl::BackgroundCallCompaction:FoundObsoleteFiles");
// delete unnecessary files if any, this is done outside the mutex
if (job_context.HaveSomethingToClean() ||
@ -1492,6 +1493,7 @@ void DBImpl::BackgroundCallCompaction(PrepickedCompaction* prepicked_compaction,
log_buffer.FlushBufferToLog();
if (job_context.HaveSomethingToDelete()) {
PurgeObsoleteFiles(job_context);
TEST_SYNC_POINT("DBImpl::BackgroundCallCompaction:PurgedObsoleteFiles");
}
job_context.Clean();
mutex_.Lock();
@ -2074,6 +2076,37 @@ void DBImpl::InstallSuperVersionAndScheduleWork(
mutable_cf_options.max_write_buffer_number;
}
// ShouldPurge is called by FindObsoleteFiles when doing a full scan,
// and db mutex (mutex_) should already be held. This function performs a
// linear scan of an vector (files_grabbed_for_purge_) in search of a
// certain element. We expect FindObsoleteFiles with full scan to occur once
// every 10 hours by default, and the size of the vector is small.
// Therefore, the cost is affordable even if the mutex is held.
// Actually, the current implementation of FindObsoleteFiles with
// full_scan=true can issue I/O requests to obtain list of files in
// directories, e.g. env_->getChildren while holding db mutex.
// In the future, if we want to reduce the cost of search, we may try to keep
// the vector sorted.
bool DBImpl::ShouldPurge(uint64_t file_number) const {
for (auto fn : files_grabbed_for_purge_) {
if (file_number == fn) {
return false;
}
}
for (const auto& purge_file_info : purge_queue_) {
if (purge_file_info.number == file_number) {
return false;
}
}
return true;
}
// MarkAsGrabbedForPurge is called by FindObsoleteFiles, and db mutex
// (mutex_) should already be held.
void DBImpl::MarkAsGrabbedForPurge(uint64_t file_number) {
files_grabbed_for_purge_.emplace_back(file_number);
}
void DBImpl::SetSnapshotChecker(SnapshotChecker* snapshot_checker) {
InstrumentedMutexLock l(&mutex_);
// snapshot_checker_ should only set once. If we need to set it multiple

48
db/db_impl_files.cc
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@ -12,6 +12,7 @@
#define __STDC_FORMAT_MACROS
#endif
#include <inttypes.h>
#include <unordered_set>
#include "db/event_helpers.h"
#include "util/file_util.h"
#include "util/sst_file_manager_impl.h"
@ -187,6 +188,13 @@ void DBImpl::FindObsoleteFiles(JobContext* job_context, bool force,
&job_context->manifest_delete_files,
job_context->min_pending_output);
// Mark the elements in job_context->sst_delete_files as grabbedForPurge
// so that other threads calling FindObsoleteFiles with full_scan=true
// will not add these files to candidate list for purge.
for (const auto sst_to_del : job_context->sst_delete_files) {
MarkAsGrabbedForPurge(sst_to_del->fd.GetNumber());
}
// store the current filenum, lognum, etc
job_context->manifest_file_number = versions_->manifest_file_number();
job_context->pending_manifest_file_number =
@ -197,6 +205,8 @@ void DBImpl::FindObsoleteFiles(JobContext* job_context, bool force,
versions_->AddLiveFiles(&job_context->sst_live);
if (doing_the_full_scan) {
InfoLogPrefix info_log_prefix(!immutable_db_options_.db_log_dir.empty(),
dbname_);
for (size_t path_id = 0; path_id < immutable_db_options_.db_paths.size();
path_id++) {
// set of all files in the directory. We'll exclude files that are still
@ -204,7 +214,21 @@ void DBImpl::FindObsoleteFiles(JobContext* job_context, bool force,
std::vector<std::string> files;
env_->GetChildren(immutable_db_options_.db_paths[path_id].path,
&files); // Ignore errors
for (std::string file : files) {
for (const std::string& file : files) {
uint64_t number;
FileType type;
// 1. If we cannot parse the file name, we skip;
// 2. If the file with file_number equals number has already been
// grabbed for purge by another compaction job, or it has already been
// schedule for purge, we also skip it if we
// are doing full scan in order to avoid double deletion of the same
// file under race conditions. See
// https://github.com/facebook/rocksdb/issues/3573
if (!ParseFileName(file, &number, info_log_prefix.prefix, &type) ||
!ShouldPurge(number)) {
continue;
}
// TODO(icanadi) clean up this mess to avoid having one-off "/" prefixes
job_context->full_scan_candidate_files.emplace_back(
"/" + file, static_cast<uint32_t>(path_id));
@ -216,7 +240,7 @@ void DBImpl::FindObsoleteFiles(JobContext* job_context, bool force,
std::vector<std::string> log_files;
env_->GetChildren(immutable_db_options_.wal_dir,
&log_files); // Ignore errors
for (std::string log_file : log_files) {
for (const std::string& log_file : log_files) {
job_context->full_scan_candidate_files.emplace_back(log_file, 0);
}
}
@ -318,6 +342,8 @@ void DBImpl::DeleteObsoleteFileImpl(int job_id, const std::string& fname,
} else {
file_deletion_status = env_->DeleteFile(fname);
}
TEST_SYNC_POINT_CALLBACK("DBImpl::DeleteObsoleteFileImpl:AfterDeletion",
&file_deletion_status);
if (file_deletion_status.ok()) {
ROCKS_LOG_DEBUG(immutable_db_options_.info_log,
"[JOB %d] Delete %s type=%d #%" PRIu64 " -- %s\n", job_id,
@ -409,6 +435,7 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state, bool schedule_only) {
std::vector<std::string> old_info_log_files;
InfoLogPrefix info_log_prefix(!immutable_db_options_.db_log_dir.empty(),
dbname_);
std::unordered_set<uint64_t> files_to_del;
for (const auto& candidate_file : candidate_files) {
std::string to_delete = candidate_file.file_name;
uint32_t path_id = candidate_file.path_id;
@ -437,6 +464,9 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state, bool schedule_only) {
// DontDeletePendingOutputs fail
keep = (sst_live_map.find(number) != sst_live_map.end()) ||
number >= state.min_pending_output;
if (!keep) {
files_to_del.insert(number);
}
break;
case kTempFile:
// Any temp files that are currently being written to must
@ -498,6 +528,19 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state, bool schedule_only) {
}
}
{
// After purging obsolete files, remove them from files_grabbed_for_purge_.
// Use a temporary vector to perform bulk deletion via swap.
InstrumentedMutexLock guard_lock(&mutex_);
std::vector<uint64_t> tmp;
for (auto fn : files_grabbed_for_purge_) {
if (files_to_del.count(fn) == 0) {
tmp.emplace_back(fn);
}
}
files_grabbed_for_purge_.swap(tmp);
}
// Delete old info log files.
size_t old_info_log_file_count = old_info_log_files.size();
if (old_info_log_file_count != 0 &&
@ -557,4 +600,5 @@ void DBImpl::DeleteObsoleteFiles() {
job_context.Clean();
mutex_.Lock();
}
} // namespace rocksdb

217
db/obsolete_files_test.cc Normal file
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@ -0,0 +1,217 @@
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#ifndef ROCKSDB_LITE
#include <stdlib.h>
#include <map>
#include <string>
#include <vector>
#include "db/db_impl.h"
#include "db/version_set.h"
#include "db/write_batch_internal.h"
#include "rocksdb/db.h"
#include "rocksdb/env.h"
#include "rocksdb/transaction_log.h"
#include "util/filename.h"
#include "util/string_util.h"
#include "util/sync_point.h"
#include "util/testharness.h"
#include "util/testutil.h"
using std::cerr;
using std::cout;
using std::endl;
using std::flush;
namespace rocksdb {
class ObsoleteFilesTest : public testing::Test {
public:
std::string dbname_;
Options options_;
DB* db_;
Env* env_;
int numlevels_;
ObsoleteFilesTest() {
db_ = nullptr;
env_ = Env::Default();
// Trigger compaction when the number of level 0 files reaches 2.
options_.level0_file_num_compaction_trigger = 2;
options_.disable_auto_compactions = false;
options_.delete_obsolete_files_period_micros = 0; // always do full purge
options_.enable_thread_tracking = true;
options_.write_buffer_size = 1024*1024*1000;
options_.target_file_size_base = 1024*1024*1000;
options_.max_bytes_for_level_base = 1024*1024*1000;
options_.WAL_ttl_seconds = 300; // Used to test log files
options_.WAL_size_limit_MB = 1024; // Used to test log files
dbname_ = test::TmpDir() + "/double_deletefile_test";
options_.wal_dir = dbname_ + "/wal_files";
// clean up all the files that might have been there before
std::vector<std::string> old_files;
env_->GetChildren(dbname_, &old_files);
for (auto file : old_files) {
env_->DeleteFile(dbname_ + "/" + file);
}
env_->GetChildren(options_.wal_dir, &old_files);
for (auto file : old_files) {
env_->DeleteFile(options_.wal_dir + "/" + file);
}
DestroyDB(dbname_, options_);
numlevels_ = 7;
EXPECT_OK(ReopenDB(true));
}
Status ReopenDB(bool create) {
delete db_;
if (create) {
DestroyDB(dbname_, options_);
}
db_ = nullptr;
options_.create_if_missing = create;
return DB::Open(options_, dbname_, &db_);
}
void CloseDB() {
delete db_;
db_ = nullptr;
}
void AddKeys(int numkeys, int startkey) {
WriteOptions options;
options.sync = false;
for (int i = startkey; i < (numkeys + startkey) ; i++) {
std::string temp = ToString(i);
Slice key(temp);
Slice value(temp);
ASSERT_OK(db_->Put(options, key, value));
}
}
int numKeysInLevels(
std::vector<LiveFileMetaData> &metadata,
std::vector<int> *keysperlevel = nullptr) {
if (keysperlevel != nullptr) {
keysperlevel->resize(numlevels_);
}
int numKeys = 0;
for (size_t i = 0; i < metadata.size(); i++) {
int startkey = atoi(metadata[i].smallestkey.c_str());
int endkey = atoi(metadata[i].largestkey.c_str());
int numkeysinfile = (endkey - startkey + 1);
numKeys += numkeysinfile;
if (keysperlevel != nullptr) {
(*keysperlevel)[(int)metadata[i].level] += numkeysinfile;
}
fprintf(stderr, "level %d name %s smallest %s largest %s\n",
metadata[i].level, metadata[i].name.c_str(),
metadata[i].smallestkey.c_str(),
metadata[i].largestkey.c_str());
}
return numKeys;
}
void createLevel0Files(int numFiles, int numKeysPerFile) {
int startKey = 0;
DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
for (int i = 0; i < numFiles; i++) {
AddKeys(numKeysPerFile, startKey);
startKey += numKeysPerFile;
ASSERT_OK(dbi->TEST_FlushMemTable());
ASSERT_OK(dbi->TEST_WaitForFlushMemTable());
}
}
void CheckFileTypeCounts(std::string& dir,
int required_log,
int required_sst,
int required_manifest) {
std::vector<std::string> filenames;
env_->GetChildren(dir, &filenames);
int log_cnt = 0, sst_cnt = 0, manifest_cnt = 0;
for (auto file : filenames) {
uint64_t number;
FileType type;
if (ParseFileName(file, &number, &type)) {
log_cnt += (type == kLogFile);
sst_cnt += (type == kTableFile);
manifest_cnt += (type == kDescriptorFile);
}
}
ASSERT_EQ(required_log, log_cnt);
ASSERT_EQ(required_sst, sst_cnt);
ASSERT_EQ(required_manifest, manifest_cnt);
}
};
TEST_F(ObsoleteFilesTest, RaceForObsoleteFileDeletion) {
createLevel0Files(2, 50000);
CheckFileTypeCounts(options_.wal_dir, 1, 0, 0);
SyncPoint::GetInstance()->LoadDependency({
{"DBImpl::BackgroundCallCompaction:FoundObsoleteFiles",
"ObsoleteFilesTest::RaceForObsoleteFileDeletion:1"},
{"DBImpl::BackgroundCallCompaction:PurgedObsoleteFiles",
"ObsoleteFilesTest::RaceForObsoleteFileDeletion:2"},
});
SyncPoint::GetInstance()->SetCallBack(
"DBImpl::DeleteObsoleteFileImpl:AfterDeletion", [&](void* arg) {
Status* p_status = reinterpret_cast<Status*>(arg);
ASSERT_TRUE(p_status->ok());
});
SyncPoint::GetInstance()->SetCallBack(
"DBImpl::CloseHelper:PendingPurgeFinished", [&](void* arg) {
std::vector<uint64_t>* files_grabbed_for_purge_ptr =
reinterpret_cast<std::vector<uint64_t>*>(arg);
ASSERT_TRUE(files_grabbed_for_purge_ptr->empty());
});
SyncPoint::GetInstance()->EnableProcessing();
DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
port::Thread user_thread([&]() {
JobContext jobCxt(0);
TEST_SYNC_POINT("ObsoleteFilesTest::RaceForObsoleteFileDeletion:1");
dbi->TEST_LockMutex();
dbi->FindObsoleteFiles(&jobCxt,
true /* force=true */, false /* no_full_scan=false */);
dbi->TEST_UnlockMutex();
TEST_SYNC_POINT("ObsoleteFilesTest::RaceForObsoleteFileDeletion:2");
dbi->PurgeObsoleteFiles(jobCxt);
jobCxt.Clean();
});
user_thread.join();
CloseDB();
}
} //namespace rocksdb
int main(int argc, char** argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
#else
#include <stdio.h>
int main(int argc, char** argv) {
fprintf(stderr,
"SKIPPED as DBImpl::DeleteFile is not supported in ROCKSDB_LITE\n");
return 0;
}
#endif // !ROCKSDB_LITE

1
src.mk
View File

@ -282,6 +282,7 @@ MAIN_SOURCES = \
db/db_write_test.cc \
db/dbformat_test.cc \
db/deletefile_test.cc \
db/obsolete_files_test.cc \
db/external_sst_file_basic_test.cc \
db/external_sst_file_test.cc \
db/fault_injection_test.cc \