fix: handle_fatal_signal (sig=6) in std::vector<std::string, std::allocator<std::string> >::_M_range_check | c++/4.8.2/bits/stl_vector.h:794 #174

Summary:
Fix for https://github.com/facebook/mysql-5.6/issues/174

When there is no old files to purge, vector.at(i) function was crashing

if (old_info_log_file_count != 0 &&
      old_info_log_file_count >= db_options_.keep_log_file_num) {
    std::sort(old_info_log_files.begin(), old_info_log_files.end());
    size_t end = old_info_log_file_count - db_options_.keep_log_file_num;
    for (unsigned int i = 0; i <= end; i++) {
      std::string& to_delete = old_info_log_files.at(i);

Added check to old_info_log_file_count be non zero.

Test Plan: run existing tests

Reviewers: gunnarku, vasilep, sdong, yhchiang

Reviewed By: yhchiang

Subscribers: andrewkr, webscalesql-eng, dhruba

Differential Revision: https://reviews.facebook.net/D55245

db/db_impl.cc

@@ -829,7 +829,8 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state) {
 
   // Delete old info log files.
   size_t old_info_log_file_count = old_info_log_files.size();
-  if (old_info_log_file_count >= db_options_.keep_log_file_num) {
+  if (old_info_log_file_count != 0 &&
+      old_info_log_file_count >= db_options_.keep_log_file_num) {
     std::sort(old_info_log_files.begin(), old_info_log_files.end());
     size_t end = old_info_log_file_count - db_options_.keep_log_file_num;
     for (unsigned int i = 0; i <= end; i++) {