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Fix deadlock between (WriterThread/Compaction/IngestExternalFile)

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Summary:
A deadlock is possible if this happen

(1) Writer thread is stopped because it's waiting for compaction to finish
(2) Compaction is waiting for current IngestExternalFile() calls to finish
(3) IngestExternalFile() is waiting to be able to acquire the writer thread
(4) WriterThread is held by stopped writes that are waiting for compactions to finish

This patch fix the issue by not incrementing num_running_ingest_file_ except when we acquire the writer thread.

This patch include a unittest to reproduce the described scenario
Closes https://github.com/facebook/rocksdb/pull/1480

Differential Revision: D4151646

Pulled By: IslamAbdelRahman

fbshipit-source-id: 09b39db
This commit is contained in:
Islam AbdelRahman 2016-11-09 10:37:51 -08:00 committed by Facebook Github Bot
parent a9fae0a9d1
commit 9bd191d2f4
2 changed files with 79 additions and 1 deletions
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4
db/db_impl.cc
View File

@ -6437,16 +6437,18 @@ Status DBImpl::IngestExternalFile(
return status;
}
TEST_SYNC_POINT("DBImpl::AddFile:Start");
{
// Lock db mutex
InstrumentedMutexLock l(&mutex_);
TEST_SYNC_POINT("DBImpl::AddFile:MutexLock");
num_running_ingest_file_++;
// Stop writes to the DB
WriteThread::Writer w;
write_thread_.EnterUnbatched(&w, &mutex_);
num_running_ingest_file_++;
// Figure out if we need to flush the memtable first
bool need_flush = false;
status = ingestion_job.NeedsFlush(&need_flush);

76
db/external_sst_file_test.cc
View File

@ -1685,6 +1685,82 @@ TEST_F(ExternalSSTFileTest, L0SortingIssue) {
ASSERT_EQ(Get(Key(7)), "memtable");
ASSERT_EQ(Get(Key(8)), "memtable");
}
TEST_F(ExternalSSTFileTest, CompactionDeadlock) {
Options options = CurrentOptions();
options.num_levels = 2;
options.level0_file_num_compaction_trigger = 4;
options.level0_slowdown_writes_trigger = 4;
options.level0_stop_writes_trigger = 4;
DestroyAndReopen(options);
// atomic conter of currently running bg threads
std::atomic<int> running_threads(0);
rocksdb::SyncPoint::GetInstance()->LoadDependency({
{"DBImpl::DelayWrite:Wait", "ExternalSSTFileTest::DeadLock:0"},
{"ExternalSSTFileTest::DeadLock:1", "DBImpl::AddFile:Start"},
{"DBImpl::AddFile:MutexLock", "ExternalSSTFileTest::DeadLock:2"},
{"ExternalSSTFileTest::DeadLock:3", "BackgroundCallCompaction:0"},
});
rocksdb::SyncPoint::GetInstance()->EnableProcessing();
// Start ingesting and extrnal file in the background
std::thread bg_ingest_file([&]() {
running_threads += 1;
ASSERT_OK(GenerateAndAddExternalFile(options, {5, 6}));
running_threads -= 1;
});
ASSERT_OK(Put(Key(1), "memtable"));
ASSERT_OK(Flush());
ASSERT_OK(Put(Key(2), "memtable"));
ASSERT_OK(Flush());
ASSERT_OK(Put(Key(3), "memtable"));
ASSERT_OK(Flush());
ASSERT_OK(Put(Key(4), "memtable"));
ASSERT_OK(Flush());
// This thread will try to insert into the memtable but since we have 4 L0
// files this thread will be blocked and hold the writer thread
std::thread bg_block_put([&]() {
running_threads += 1;
ASSERT_OK(Put(Key(10), "memtable"));
running_threads -= 1;
});
// Make sure DelayWrite is called first
TEST_SYNC_POINT("ExternalSSTFileTest::DeadLock:0");
// `DBImpl::AddFile:Start` will wait until we be here
TEST_SYNC_POINT("ExternalSSTFileTest::DeadLock:1");
ASSERT_EQ(running_threads.load(), 2);
// Wait for IngestExternalFile() to start and aquire mutex
TEST_SYNC_POINT("ExternalSSTFileTest::DeadLock:2");
// Now let compaction start
TEST_SYNC_POINT("ExternalSSTFileTest::DeadLock:3");
// Wait for max 5 seconds, if we did not finish all bg threads
// then we hit the deadlock bug
for (int i = 0; i < 10; i++) {
if (running_threads.load() == 0) {
break;
}
env_->SleepForMicroseconds(500000);
}
ASSERT_EQ(running_threads.load(), 0);
bg_ingest_file.join();
bg_block_put.join();
}
#endif // ROCKSDB_LITE
} // namespace rocksdb