Below are my gem versions -

gem 'rails', '5.1.1'
gem 'mysql2'
ruby:2.5.0

I am trying to utilise the multiple cores available, using Parallel gem to do a heavy time consuming task.

Parallel.map(ranges, :in_processes =>2) do |range|
       require 'parallel'
       @items_dao.reconnect
       #doStuff
       0  
     end

But I keep getting Segmentation fault -

/usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/mysql2.rb:159: [BUG] Segmentation fault at 0x00007f1cb91518b8
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0069 p:---- s:0427 e:000426 CFUNC  :each
c:0068 p:0036 s:0422 e:000421 BLOCK  /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/mysql2.rb:159
c:0067 p:0085 s:0418 E:001d50 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/mysql2.rb:90
c:0066 p:0014 s:0406 e:000405 BLOCK  /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/shared/mysql_prepared_statements.rb:34
c:0065 p:0005 s:0402 e:000401 BLOCK  /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/database/connecting.rb:250
c:0064 p:0030 s:0398 e:000397 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/connection_pool/threaded.rb:85
c:0063 p:0018 s:0387 e:000386 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/database/connecting.rb:250
c:0062 p:0068 s:0382 e:000381 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/shared/mysql_prepared_statements.rb:34
c:0061 p:0058 s:0375 e:000374 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/dataset/actions.rb:908
c:0060 p:0040 s:0367 e:000366 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/mysql2.rb:191
c:0059 p:0007 s:0360 E:001dc8 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/adapters/mysql2.rb:153
c:0058 p:0029 s:0355 E:0022e8 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/dataset/actions.rb:139
c:0057 p:0100 s:0350 E:000fb8 METHOD /usr/local/bundle/gems/sequel-4.18.0/lib/sequel/dataset/actions.rb:740

Stack trace is really big, all the gems get listed at the last it is Error: Parallel::DeadWorker

If I use Parallel.map(ranges, :in_processes =>1) then also i get the same error.

If i use Parallel.map(ranges, :in_processes => 0 ) do |range| then it works fine, but obviously there is no parallelism.

If i use Parallel.map(ranges, :in_threads => 2 ) do |range| instead of 'in_processes', then it works fine, but it just uses one core.

I have read at multiple places that mostly its the mysql version, but I have tried that also, i just get a different gem with Segmentation fault. Let me know if more information is required.

So i updated the mysql and ruby version

gem 'mysql2', '~> 0.5.3'
ruby:2.6.0

and ran the code with 4 processes Parallel.map(ranges, :in_processes => 4 ) do |range| the workers ran for some time but slowly they got killed one by one with the below errors. But yeah they ran for much longer than yesterday when i was on older gem versions.

E0303 13:41:01.578019480       9 ssl_transport_security.cc:510] Corruption detected.
E0303 13:41:01.578086834       9 ssl_transport_security.cc:486] error:100003fc:SSL routines:OPENSSL_internal:SSLV3_ALERT_BAD_RECORD_MAC
E0303 13:41:01.578096288       9 secure_endpoint.cc:208]     Decryption error: TSI_DATA_CORRUPTED
E0303 13:41:01.579091347      36 ssl_transport_security.cc:510] Corruption detected.
E0303 13:41:01.579368866      36 ssl_transport_security.cc:486] error:100003fc:SSL routines:OPENSSL_internal:SSLV3_ALERT_BAD_RECORD_MAC
E0303 13:41:01.579534771      36 secure_endpoint.cc:208]     Decryption error: TSI_DATA_CORRUPTED
E0303 13:41:01.579499119      48 ssl_transport_security.cc:510] Corruption detected.
E0303 13:41:01.580041527      48 ssl_transport_security.cc:486] error:100003fc:SSL routines:OPENSSL_internal:SSLV3_ALERT_BAD_RECORD_MAC
E0303 13:41:01.580167078      48 secure_endpoint.cc:208]     Decryption error: TSI_DATA_CORRUPTED
E0303 13:41:01.580940403      78 ssl_transport_security.cc:510] Corruption detected.
E0303 13:41:01.581021246      78 ssl_transport_security.cc:486] error:100003fc:SSL routines:OPENSSL_internal:SSLV3_ALERT_BAD_RECORD_MAC
E0303 13:41:01.581055435      78 secure_endpoint.cc:208]     Decryption error: TSI_DATA_CORRUPTED
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/ivar.rb:169: [BUG] Segmentation fault at 0x00007efe599b2270
ruby 2.6.0p0 (2018-12-25 revision 66547) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0010 p:0028 s:0055 e:000051 METHOD /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/ivar.rb:169
c:0009 p:0010 s:0043 e:000042 METHOD /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/scheduled_task.rb:285
c:0008 p:0006 s:0039 e:000038 BLOCK  /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/timer_set.rb:165
c:0007 p:0009 s:0036 e:000035 METHOD /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:363
c:0006 p:0049 s:0028 e:000027 BLOCK  /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:352 [FINISH]
c:0005 p:---- s:0022 e:000021 CFUNC  :loop
c:0004 p:0006 s:0018 e:000017 BLOCK  /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:335 [FINISH]
c:0003 p:---- s:0015 e:000014 CFUNC  :catch
c:0002 p:0020 s:0010 e:000009 BLOCK  /usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:334 [FINISH]
c:0001 p:---- s:0003 e:000002 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:334:in `block in create_worker'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:334:in `catch'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:335:in `block (2 levels) in create_worker'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:335:in `loop'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:352:in `block (3 levels) in create_worker'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/ruby_thread_pool_executor.rb:363:in `run_task'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/executor/timer_set.rb:165:in `block (2 levels) in process_tasks'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/scheduled_task.rb:285:in `process_task'
/usr/local/bundle/gems/concurrent-ruby-1.1.8/lib/concurrent-ruby/concurrent/ivar.rb:169:in `safe_execute'

-- Machine register context ------------------------------------------------
 RIP: 0x00007efe8f8043c5 RBP: 0x0000000000000009 RSP: 0x00007efe942d99a8
 RAX: 0x00005555db9a2d94 RBX: 0x0000000000000003 RCX: 0x0000000000000001
 RDX: 0x0000000000000002 RDI: 0x00007efe599b2270 RSI: 0x0000000000000000
  R8: 0x00000000283ceef8  R9: 0x000000000002cc54 R10: 0x00000000ffffffff
 R11: 0x0000000000000000 R12: 0x0000000000000005 R13: 0x00007efe599b2230
 R14: 0x0000000000000000 R15: 0x00005555db9a2d70 EFL: 0x0000000000010202

Any thoughts on this?