Re: [Tarantool-patches] [PATCH 7/7] box: make promote/demote always bump the term

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

19.06.2021 01:53, Vladislav Shpilevoy пишет:
> Thanks for the patch!
>
> See 4 comments below.
>
>>      box: make promote always bump the term
>>      
>>      When called without elections, promote and resulted in multiple
> 1. 'and' is excess.

Thanks, fixed.

>
>>      PROMOTE entries for the same term. This is not right, because all
>>      the promotions for the same term except the first one would be ignored
>>      as already seen.
>>      
>>      Part-of #6034
>>
>> diff --git a/src/box/box.cc b/src/box/box.cc
>> index 6a0950f44..53a8f80e5 100644
>> --- a/src/box/box.cc
>> +++ b/src/box/box.cc
>> @@ -1687,16 +1687,18 @@ box_promote(void)
>>   			rc = -1;
>>   		} else {
>>   promote:
>> -			/* We cannot possibly get here in a volatile state. */
>> -			assert(box_raft()->volatile_term == box_raft()->term);
>> +			if (try_wait)
>> +				raft_new_term(box_raft());
> 2. It starts to bother me, that we use try_wait flag as a kind of a
> state of the promote process rather just just a command 'you need to wait'.
> But I can't propose anything better right away. Just noticing.

I agree. I'd like to refactor box_clear_synchro_queue()/box_ctl_promote()
sometime soon. It starts to look really bad in my opinion.

>
>> diff --git a/test/replication/gh-4114-local-space-replication.result b/test/replication/gh-4114-local-space-replication.result
>> index 9b63a4b99..676400cef 100644
>> --- a/test/replication/gh-4114-local-space-replication.result
>> +++ b/test/replication/gh-4114-local-space-replication.result> @@ -77,9 +76,9 @@ box.space.test:insert{3}
>>    | - [3]
>>    | ...
>>   
>> -box.info.vclock[0]
>> +box.info.vclock[0] == a + 3 or box.info.vclock[0] - a
> 3. Maybe use an assertion? They really do look easier to read
> when you try to understand a test.

Ok, sure.

>
>>    | ---
>> - | - 3
>> + | - true
>>    | ...
>> diff --git a/test/replication/gh-6034-promote-bump-term.result b/test/replication/gh-6034-promote-bump-term.result
>> new file mode 100644
>> index 000000000..20e352922
>> --- /dev/null
>> +++ b/test/replication/gh-6034-promote-bump-term.result
>> @@ -0,0 +1,37 @@
>> +-- test-run result file version 2
>> +test_run = require('test_run').new()
>> + | ---
>> + | ...
>> +
>> +-- gh-6034: test that every box.ctl.promote() bumps
>> +-- the instance's term. Even when elections are disabled. Even for consequent
>> +-- promotes on the same instance.
>> +election_mode = box.cfg.election_mode
>> + | ---
>> + | ...
>> +box.cfg{election_mode='off'}
>> + | ---
>> + | ...
>> +
>> +term = box.info.election.term
>> + | ---
>> + | ...
>> +box.ctl.promote()
>> + | ---
>> + | ...
>> +assert(box.info.election.term == term + 1)
>> + | ---
>> + | - true
>> + | ...
>> +box.ctl.promote()
>> + | ---
>> + | ...
>> +assert(box.info.election.term == term + 2)
>> + | ---
>> + | - true
> 4. Could you please remind why do we issue a new promote even
> if we own the limbo already?
>
> Especially if its ownership is going to get ever more strict
> after this series.
>

Hmm. I just didn't change that behaviour.

Why not though? Since it bumps the term as well.

Say, when promote is issued in 'manual' election mode,
it results in a new election every time.

So, why not make it bump the term for each consequent call
even when elections are off?


Here's the diff:

=======================================

diff --git a/test/replication/gh-4114-local-space-replication.result 
b/test/replication/gh-4114-local-space-replication.result
index 676400cef..e71eb60a8 100644
--- a/test/replication/gh-4114-local-space-replication.result
+++ b/test/replication/gh-4114-local-space-replication.result
@@ -76,7 +76,7 @@ box.space.test:insert{3}
   | - [3]
   | ...

-box.info.vclock[0] == a + 3 or box.info.vclock[0] - a
+assert(box.info.vclock[0] == a + 3)
   | ---
   | - true
   | ...
diff --git a/test/replication/gh-4114-local-space-replication.test.lua 
b/test/replication/gh-4114-local-space-replication.test.lua
index 8f787db84..65fef3bf6 100644
--- a/test/replication/gh-4114-local-space-replication.test.lua
+++ b/test/replication/gh-4114-local-space-replication.test.lua
@@ -27,7 +27,7 @@ box.space.test:insert{2}
  box.snapshot()
  box.space.test:insert{3}

-box.info.vclock[0] == a + 3 or box.info.vclock[0] - a
+assert(box.info.vclock[0] == a + 3)

  test_run:cmd('switch default')




=======================================

-- 
Serge Petrenko