CompactRange (c++) causes segfault

[stephan-hof]

Hi guys,

I need a bit of support. In my application code there is this line

this->db->CompactRange(this->cf_handle, NULL, NULL, true);

Unfortunately the program aborts with a segfault. I already attached gdb to it having the following back-trace

#0  rocksdb::SomeFileOverlapsRange (icmp=..., disjoint_sorted_files=<optimized out>, file_level=..., smallest_user_key=0x0, largest_user_key=0x0) at db/version_set.cc:398
#1  0x00007ffff5e80d74 in rocksdb::DBImpl::CompactRange (this=0x1088750, column_family=<optimized out>, begin=0x0, end=0x0, reduce_level=true, target_level=-1, target_path_id=0)
    at db/db_impl.cc:1158
#2  0x00007ffff5e3cab5 in DataStore::compact (this=0xde2598) at cpp/data_store.cpp:151

I investigated the rocksdb code a bit and the following two parts puzzle me how they interact with 'level_files_brief_'

/* Part one. */
Status DBImpl::CompactRange(C.....
    for (int level = 1; level < cfd->NumberLevels(); level++) {
      if (base->storage_info()->OverlapInLevel(level, begin, end)) {

bool VersionStorageInfo::OverlapInLevel(int level,
                                        const Slice* smallest_user_key,
                                        const Slice* largest_user_key) {
  return SomeFileOverlapsRange(*internal_comparator_, (level > 0),
                               level_files_brief_[level], smallest_user_key,
                               largest_user_key);
}

In my case NumberLevels() is 10.

/* Part two. */
void VersionStorageInfo::GenerateLevelFilesBrief() {
  level_files_brief_.resize(num_non_empty_levels_);
  for (int level = 0; level < num_non_empty_levels_; level++) {

In my case num_non_empty_levels_ is 2.

From my point of view OverlapInLevel is called with level=0,1,2,3,4,5...9 however level_files_brief_ has only size 2. So there is an 'out of range' access. I'm using 3.9.fb, but the code in question is also in master.

If you need more input from my side feel free to ask. It is easy to reproduce and the environment is under full control.

[igorcanadi]

Thanks for a great bug report!

Wow I'm not sure how we never caught this before. Fix here: https://reviews.facebook.net/D37779

[igorcanadi]

(BTW to test it out, you can do arc patch D37779 on the repository. You'll need to install arcanist -- https://secure.phabricator.com/book/phabricator/article/arcanist/)

[stephan-hof]

Hi the patch works in my scenario. Thanks for the quick response.

[igorcanadi]

Glad to help @stephan-hof !