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[RocksDB] make sure KSVObsolete does not get accessed as a valid pointer. 

Summary: KSVObsolete is no longer nullptr and needs to be checked explicitly. Also did some minor code cleanup and added a stat counter to track superversion cleanups incurred in the foreground.

Test Plan: make check

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16701
This commit is contained in:
Haobo Xu 2014-03-08 21:12:13 -08:00
parent cff908db09
commit 9e0e6aa7f6
3 changed files with 13 additions and 6 deletions
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16
db/db_impl.cc
View File

@ -541,6 +541,7 @@ bool DBImpl::SuperVersion::Unref() {
}
void DBImpl::SuperVersion::Cleanup() {
db->mutex_.AssertHeld();
assert(refs.load(std::memory_order_relaxed) == 0);
imm->Unref(&to_delete);
MemTable* m = mem->Unref();
@ -552,6 +553,7 @@ void DBImpl::SuperVersion::Cleanup() {
void DBImpl::SuperVersion::Init(MemTable* new_mem, MemTableListVersion* new_imm,
Version* new_current) {
db->mutex_.AssertHeld();
mem = new_mem;
imm = new_imm;
current = new_current;
@ -2960,8 +2962,10 @@ Status DBImpl::GetImpl(const ReadOptions& options,
// acquiring mutex for this operation, we use atomic Swap() on the thread
// local pointer to guarantee exclusive access. If the thread local pointer
// is being used while a new SuperVersion is installed, the cached
// SuperVersion can become stale. It will eventually get refreshed either
// on the next GetImpl() call or next SuperVersion installation.
// SuperVersion can become stale. In that case, the background thread would
// have swapped in kSVObsolete. We re-check the value at the end of
// Get, with an atomic compare and swap. The superversion will be released
// if detected to be stale.
void* ptr = local_sv_->Swap(SuperVersion::kSVInUse);
// Invariant:
// (1) Scrape (always) installs kSVObsolete in ThreadLocal storage
@ -2976,7 +2980,10 @@ Status DBImpl::GetImpl(const ReadOptions& options,
SuperVersion* sv_to_delete = nullptr;
if (sv && sv->Unref()) {
RecordTick(options_.statistics.get(), NUMBER_SUPERVERSION_CLEANUPS);
mutex_.Lock();
// TODO underlying resources held by superversion (sst files) might
// not be released until the next background job.
sv->Cleanup();
sv_to_delete = sv;
} else {
@ -3051,15 +3058,12 @@ Status DBImpl::GetImpl(const ReadOptions& options,
if (unref_sv) {
// Release SuperVersion
bool delete_sv = false;
if (sv->Unref()) {
mutex_.Lock();
sv->Cleanup();
mutex_.Unlock();
delete_sv = true;
}
if (delete_sv) {
delete sv;
RecordTick(options_.statistics.get(), NUMBER_SUPERVERSION_CLEANUPS);
}
RecordTick(options_.statistics.get(), NUMBER_SUPERVERSION_RELEASES);
}

1
db/db_impl.h
View File

@ -291,6 +291,7 @@ class DBImpl : public DB {
private:
friend class DB;
friend class TailingIterator;
friend struct SuperVersion;
struct CompactionState;
struct Writer;

2
include/rocksdb/statistics.h
View File

@ -124,6 +124,7 @@ enum Tickers {
NUMBER_DIRECT_LOAD_TABLE_PROPERTIES,
NUMBER_SUPERVERSION_ACQUIRES,
NUMBER_SUPERVERSION_RELEASES,
NUMBER_SUPERVERSION_CLEANUPS,
TICKER_ENUM_MAX
};
@ -181,6 +182,7 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
"rocksdb.number.direct.load.table.properties"},
{NUMBER_SUPERVERSION_ACQUIRES, "rocksdb.number.superversion_acquires"},
{NUMBER_SUPERVERSION_RELEASES, "rocksdb.number.superversion_releases"},
{NUMBER_SUPERVERSION_CLEANUPS, "rocksdb.number.superversion_cleanups"},
};
/**