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Allow mutex to be released in GetAggregatedIntProperty (#7412)

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Summary:
Current implementation holds db mutex while calling
`GetAggregatedIntProperty()`. For property kEstimateTableReadersMem,
this can be expensive, especially if the number of table readers is
high.
We can release and re-acquire db mutex if
property_info.need_out_of_mutex is true.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7412

Test Plan:
make check
COMPILE_WITH_ASAN=1 make check
COMPILE_WITH_TSAN=1 make check
Also test internally on a shadow host. Used bpf to verify the
excessively long db mutex holding no longer exists when applications
call GetApproximateMemoryUsageByType().

Reviewed By: jay-zhuang

Differential Revision: D23794824

Pulled By: riversand963

fbshipit-source-id: 6bc02a59fd25613d343a62cf817467c7122c9721
This commit is contained in:
Yanqin Jin 2020-09-22 12:35:58 -07:00 committed by Facebook GitHub Bot
parent 29f7bbef99
commit cd72f8974b
1 changed files with 16 additions and 9 deletions
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25
db/db_impl/db_impl.cc
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@ -3135,17 +3135,17 @@ bool DBImpl::GetIntPropertyInternal(ColumnFamilyData* cfd,
}
} else {
SuperVersion* sv = nullptr;
if (!is_locked) {
sv = GetAndRefSuperVersion(cfd);
} else {
sv = cfd->GetSuperVersion();
if (is_locked) {
mutex_.Unlock();
}
sv = GetAndRefSuperVersion(cfd);
bool ret = cfd->internal_stats()->GetIntPropertyOutOfMutex(
property_info, sv->current, value);
if (!is_locked) {
ReturnAndCleanupSuperVersion(cfd, sv);
ReturnAndCleanupSuperVersion(cfd, sv);
if (is_locked) {
mutex_.Lock();
}
return ret;
@ -3182,6 +3182,7 @@ bool DBImpl::GetAggregatedIntProperty(const Slice& property,
}
uint64_t sum = 0;
bool ret = true;
{
// Needs mutex to protect the list of column families.
InstrumentedMutexLock l(&mutex_);
@ -3190,15 +3191,21 @@ bool DBImpl::GetAggregatedIntProperty(const Slice& property,
if (!cfd->initialized()) {
continue;
}
if (GetIntPropertyInternal(cfd, *property_info, true, &value)) {
cfd->Ref();
ret = GetIntPropertyInternal(cfd, *property_info, true, &value);
// GetIntPropertyInternal may release db mutex and re-acquire it.
mutex_.AssertHeld();
cfd->UnrefAndTryDelete();
if (ret) {
sum += value;
} else {
return false;
ret = false;
break;
}
}
}
*aggregated_value = sum;
return true;
return ret;
}
SuperVersion* DBImpl::GetAndRefSuperVersion(ColumnFamilyData* cfd) {