Fix a bug in MANIFEST group commit

[riversand963]

PR #3944 introduces group commit of VersionEdit in MANIFEST. The
implementation has a bug. When updating the log file number of each column
family, we must consider only VersionEdits that operate on the same column
family. Otherwise, a column family may accidentally set its log file number
higher than actual value, indicating that log files with smaller file number
will be ignored, thus causing some updates to be lost.

Test plan:

$make clean && make -j16 all check
$./db_stress -set_options_one_in=20 -ingest_external_file_one_in=20 -nooverwritepercent=0 -ops_per_thread=10000

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[ajkr]

nice

[DorianZheng]

@riversand963 Thank you fox fixing this bug, but I have a question about this PR. I found that VersionSet::LogAndApplyHelper has codes like this:

  if (edit->has_log_number_) {
    assert(edit->log_number_ >= cfd->GetLogNumber());
    assert(edit->log_number_ < next_file_number_.load());
  }

So If we ignore some log number, Isn't it asserting fail?

[riversand963]

@DorianZheng I think there is some confusion about 'ignoring'. PR #4157 does not violate the assertions because newer version edit will always have larger file number than current column family.

Original code may mistakenly set the column family's log file number (cfd->GetLogNumber()) to a higher value while some of the updates to the column family reside in a lower log. The log files with smaller number will be ignored, causing some updates to be missing.