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Fix WAL corruption from checkpoint/backup race condition

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Summary:
`Writer::WriteBuffer` was always called at the beginning of checkpoint/backup. But that log writer has no internal synchronization, which meant the same buffer could be flushed twice in a race condition case, causing a WAL entry to be duplicated. Then subsequent WAL entries would be at unexpected offsets, causing the 32KB block boundaries to be overlapped and manifesting as a corruption.

This PR fixes the behavior to only use `WriteBuffer` (via `FlushWAL`) in checkpoint/backup when manual WAL flush is enabled. In that case, users are responsible for providing synchronization between WAL flushes. We can also consider removing the call entirely.
Closes https://github.com/facebook/rocksdb/pull/3603

Differential Revision: D7277447

Pulled By: ajkr

fbshipit-source-id: 1b15bd7fd930511222b075418c10de0aaa70a35a
This commit is contained in:
Andrew Kryczka 2018-03-16 14:15:53 -07:00
parent dbd8fa09b8
commit 06858ac58d
2 changed files with 7 additions and 1 deletions
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4
HISTORY.md
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@ -1,4 +1,8 @@
# Rocksdb Change Log
## Unreleased
### Bug Fixes
* Fix WAL corruption caused by race condition between user write thread and backup/checkpoint thread.
## 5.11.2 (02/24/2018)
### Bug Fixes
* Fix bug in iterator readahead causing blocks to incorrectly be considered truncated (corrupted).

4
utilities/checkpoint/checkpoint_impl.cc
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@ -207,7 +207,9 @@ Status CheckpointImpl::CreateCustomCheckpoint(
TEST_SYNC_POINT("CheckpointImpl::CreateCheckpoint:SavedLiveFiles1");
TEST_SYNC_POINT("CheckpointImpl::CreateCheckpoint:SavedLiveFiles2");
db_->FlushWAL(false /* sync */);
if (db_options.manual_wal_flush) {
db_->FlushWAL(false /* sync */);
}
}
// if we have more than one column family, we need to also get WAL files
if (s.ok()) {