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Fix a data race between GetColumnFamilyMetaData and MarkFilesBeingCompacted (#6056) 

Summary:
Use db mutex to protect the execution of Version::GetColumnFamilyMetaData()
called in DBImpl::GetColumnFamilyMetaData().
Without mutex, GetColumnFamilyMetaData() races with MarkFilesBeingCompacted()
for access to FileMetaData::being_compacted.
Other than mutex, there are several more alternatives.

- Make FileMetaData::being_compacted an atomic variable. This will make
  FileMetaData non-copy-able.

- Separate being_compacted from FileMetaData. This requires re-organizing data
  structures that are already used in many places.

Test Plan (dev server):
```
make check
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6056

Differential Revision: D18620488

Pulled By: riversand963

fbshipit-source-id: 87f89660b5d5e2ab4ef7962b7b2a7d00e346aa3b
This commit is contained in:
Yanqin Jin 2019-11-20 16:32:17 -08:00 committed by Facebook Github Bot
parent c0983d0691
commit 0ce0edbe12
2 changed files with 14 additions and 1 deletions
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1
HISTORY.md
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@ -2,6 +2,7 @@
## Unreleased
### Bug Fixes
* Fix data corruption casued by output of intra-L0 compaction on ingested file not being placed in correct order in L0.
* Fix a data race between Version::GetColumnFamilyMetaData() and Compaction::MarkFilesBeingCompacted() for access to being_compacted (#6056). The current fix acquires the db mutex during Version::GetColumnFamilyMetaData(), which may cause regression.
### Public API Change
* TTL Compactions in Level compaction style now initiate successive cascading compactions on a key range so that it reaches the bottom level quickly on TTL expiry. `creation_time` table property for compaction output files is now set to the minimum of the creation times of all compaction inputs.

12
db/db_impl/db_impl.cc
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@ -3241,7 +3241,19 @@ void DBImpl::GetColumnFamilyMetaData(ColumnFamilyHandle* column_family,
assert(column_family);
auto* cfd = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family)->cfd();
auto* sv = GetAndRefSuperVersion(cfd);
{
// Without mutex, Version::GetColumnFamilyMetaData will have data race with
// Compaction::MarkFilesBeingCompacted. One solution is to use mutex, but
// this may cause regression. An alternative is to make
// FileMetaData::being_compacted atomic, but it will make FileMetaData
// non-copy-able. Another option is to separate these variables from
// original FileMetaData struct, and this requires re-organization of data
// structures. For now, we take the easy approach. If
// DB::GetColumnFamilyMetaData is not called frequently, the regression
// should not be big. We still need to keep an eye on it.
InstrumentedMutexLock l(&mutex_);
sv->current->GetColumnFamilyMetaData(cf_meta);
}
ReturnAndCleanupSuperVersion(cfd, sv);
}