[infinispan-dev] rethinking ISPN transactions

[Radim Vansa]

Mircea, besides mentioning of removed stuff, would it be possible to 
compile some list of supported transactional modes and *expected 
behaviour*? (using short code snippets: in one mode this will fail, in 
other one succeed) Ideally, total order could be included there as well.

This list should provide the rationale for each mode. Maybe I could then 
provide some numbers for each mode to let user see whether the lower 
guarantees are worth the performance impact.

Also, I'd like to see there presented the problem with transactional 
reads - to let users know that if you write two values inside the 
transaction and commit it, in another transaction you may read one of 
the entries as appeared before the commit and another as appeared after. 
I know that this can be evaded by force locking, and I understand why 
this happens but when user reads /transactions/, he sees /ACID 
properties/. And this (default) unexpected behaviour kind of breaks 
isolation - user needs to be aware of that (and I haven't seen this 
written down anywhere in the docs).

Radim

On 11/12/2013 12:56 PM, Galder Zamarreño wrote:
> On Nov 8, 2013, at 4:28 PM, Mircea Markus <mmarkus at redhat.com> wrote:
>
>> Hey guys,
>>
>> Several things were discussed lately([1],[2],[3],[4]) around our transaction support. Here's some some thoughts I have around re-modeling transactions for 7.0:
>>
>> 1. Async options for commit/rollback
>> - they don't really make sense as a user you don't get any guarantee on the status of the transaction
>> - they complicate the code significantly
>> - I think they should be removed
> So, they're always sync, right?
>
>> 2. READ_COMMITTED
>> - it has the same performance as REPEATABLE_READ, but offers less guarantees.
>> - unlike REPEATABLE_READ, it also behaves inconsistently when the data is owned by transaction originator
>> - I think it should be removed
> +1. So, if you remove RC, and we only have RR, you can get rid of the isolation level configuration property altogether? We don't implement SERIALIZABLE, nor READ_UNCOMMITTED.
>
>> 3. Optimistic tx without Write Skew Check (WSC)
>> - well, without WSC the transactions are not optimistic by definition
>> - they are something else: an batch update of multiple key/values. If the batch is successful you know the update was atomic. If it failed you don't get any guarantee
>> - suggestion: optimistic tx should *always* have WSC enabled (no option to configure it)
> +1
>
> FYI, this means that the default OL behaivour changes. To be more precise, here's [1] a Gist with the difference in expectations for default configuration.
>
> [1] https://gist.github.com/galderz/9ba22e47116906a750d7
>
>> - build our batching functionality on top of what currently is optimistic tx without WSC and document it as such
>>
>> 4. Remove 1PC option
>> - I'm not totally sure about it, but does it really make sense to have 1PC as an option? they don't offer any consistency guarantees so async API + non tx do about the same thing
> +1
>
>>
>> [1] http://markmail.org/thread/a7fjko4dyejxqgdy
>> [2] https://github.com/infinispan/infinispan/pull/2177
>> [3] http://infinispan.markmail.org/thread/nl2bs7rjvayjcybv
>> [4] http://infinispan.markmail.org/thread/vbg6g4otu7djazbc
>>
>>
>> Cheers,
>> -- 
>> Mircea Markus
>> Infinispan lead (www.infinispan.org)
>>
>>
>>
>>
>>
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>
> --
> Galder Zamarreño
> galder at redhat.com
> twitter.com/galderz
>
> Project Lead, Escalante
> http://escalante.io
>
> Engineer, Infinispan
> http://infinispan.org
>
>
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-- 
Radim Vansa <rvansa at redhat.com>
JBoss DataGrid QA