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Set logs as getting flushed before releasing lock, race condition fix 

Summary:
Relating to #1903:

In MaybeFlushColumnFamilies() we want to modify the 'getting_flushed' flag before releasing the db mutex when SwitchMemtable() is called.

The following 2 actions need to be atomic in MaybeFlushColumnFamilies()
- getting_flushed is false on oldest log
- we determine that all CFs can be flushed to successfully release oldest log
- we set getting_flushed = true on the oldest log.
-------
- getting_flushed is false on oldest log
- we determine that all CFs can NOT be flushed to successfully release oldest log
- we set unable_to_flush_oldest_log_ = true on the oldest log.

#### In the 2pc case:

T1 enters function but is unable to flush all CFs to release log
T1 sets unable_to_flush_oldest_log_ = true
T1 begins flushing all CFs possible

T2 enters function but is unable to flush all CFs to release log
T2 sees unable_to_flush_oldes_log_ has been set so exits

T3 enters function and will be able to flush all CFs to release oldest log
T3 sets getting_flushed = true on oldes
Closes https://github.com/facebook/rocksdb/pull/1909

Differential Revision: D4646235

Pulled By: reidHoruff

fbshipit-source-id: c8d0447
This commit is contained in:
Reid Horuff 2017-03-06 15:04:36 -08:00 committed by Facebook Github Bot
parent f8a4ea0206
commit 58b12dfe37
1 changed files with 17 additions and 25 deletions
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42
db/db_impl.cc
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@ -5053,14 +5053,25 @@ void DBImpl::MaybeFlushColumnFamilies() {
auto oldest_log_with_uncommited_prep = FindMinLogContainingOutstandingPrep();
if (allow_2pc() &&
unable_to_flush_oldest_log_ &&
oldest_log_with_uncommited_prep > 0 &&
oldest_log_with_uncommited_prep <= oldest_alive_log) {
// we already attempted to flush all column families dependent on
// the oldest alive log but the log still contained uncommited transactions.
// the oldest alive log STILL contains uncommited transaction so there
// is still nothing that we can do.
return;
if (unable_to_flush_oldest_log_) {
// we already attempted to flush all column families dependent on
// the oldest alive log but the log still contained uncommited transactions.
// the oldest alive log STILL contains uncommited transaction so there
// is still nothing that we can do.
return;
} else {
Log(InfoLogLevel::WARN_LEVEL, immutable_db_options_.info_log,
"Unable to release oldest log due to uncommited transaction");
unable_to_flush_oldest_log_ = true;
}
} else {
// we only mark this log as getting flushed if we have successfully
// flushed all data in this log. If this log contains outstanding prepared
// transactions then we cannot flush this log until those transactions are commited.
unable_to_flush_oldest_log_ = false;
alive_log_files_.begin()->getting_flushed = true;
}
WriteContext context;
@ -5086,25 +5097,6 @@ void DBImpl::MaybeFlushColumnFamilies() {
}
MaybeScheduleFlushOrCompaction();
// we only mark this log as getting flushed if we have successfully
// flushed all data in this log. If this log contains outstanding prepred
// transactions then we cannot flush this log until those transactions are commited.
unable_to_flush_oldest_log_ = false;
if (allow_2pc()) {
if (oldest_log_with_uncommited_prep == 0 ||
oldest_log_with_uncommited_prep > oldest_alive_log) {
// this log contains no outstanding prepared transactions
alive_log_files_.begin()->getting_flushed = true;
} else {
Log(InfoLogLevel::WARN_LEVEL, immutable_db_options_.info_log,
"Unable to release oldest log due to uncommited transaction");
unable_to_flush_oldest_log_ = true;
}
} else {
alive_log_files_.begin()->getting_flushed = true;
}
}
uint64_t DBImpl::GetMaxTotalWalSize() const {