Re: Horizontal scalability/sharding

On 2015-09-02 PM 04:07, Albe Laurenz wrote:
> Amit Langote wrote:
>> On 2015-09-02 PM 03:25, Amit Kapila wrote:
>>> Will it handle deadlocks across different table partitions. Consider
>>> a case as below:
>>>
>>> T1
>>> 1. Updates row R1 of T1 on shard S1
>>> 2. Updates row R2 of T2 on shard S2
>>>
>>> T2
>>> 1. Updates row R2 of T2 on shard S2
>>> 2. Updates row R1 of T1 on shard S1
> 
>> As long as shards are processed in the same order in different
>> transactions, ISTM, this issue should not arise? I can imagine it becoming
>> a concern if parallel shard processing enters the scene. Am I missing
>> something?
> 
> That would only hold for a single query, right?
> 
> If 1. and 2. in the above example come from different queries within one
> transaction, you cannot guarantee that shards are processed in the same order.
> 
> So T1 and T2 could deadlock.
> 

Sorry, I failed to see why that would be the case. Could you elaborate?

Thanks,
Amit