fix: Round-Robin pri under leveled compaction allows subcompactions b…

[Chdy]

Summary: Round-Robin pri under leveled compaction allows subcompactions by default is not compatible with PlainTable

bool Compaction::ShouldFormSubcompactions() const {
  if (cfd_ == nullptr) {
    return false;
  }

  // Round-Robin pri under leveled compaction allows subcompactions by default
  // and the number of subcompactions can be larger than max_subcompactions_
  if (cfd_->ioptions()->compaction_pri == kRoundRobin &&
      cfd_->ioptions()->compaction_style == kCompactionStyleLevel) {
    return output_level_ > 0;
  }

  if (max_subcompactions_ <= 1) {
    return false;
  }

PlainTable does not support Subcompaction, including when AdaptiveTable is applied to PlainTable. subcompaction by default will result in the following error in some scenarios.

void PlainTableIterator::Seek(const Slice& target) {
  if (use_prefix_seek_ != !table_->IsTotalOrderMode()) {
    // This check is done here instead of NewIterator() to permit creating an
    // iterator with total_order_seek = true even if we won't be able to Seek()
    // it. This is needed for compaction: it creates iterator with
    // total_order_seek = true but usually never does Seek() on it,
    // only SeekToFirst().
    status_ = Status::InvalidArgument(
        "total_order_seek not implemented for PlainTable.");
    offset_ = next_offset_ = table_->file_info_.data_end_offset;
    return;
  }

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@cbi42 has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@cbi42 merged this pull request in facebook/rocksdb@110ce5f4a392d02167cee3439160f83d2929a2c8.