[infinispan-dev] API behaviour when using DIST
Bela Ban
bban at redhat.com
Fri Apr 24 01:52:41 EDT 2009
Whatever you do, I think quick'n'dirty fire&forget calls are important:
a user might want to push data into the grid at a very high rate and
does not care about return values (for now).
Maybe an additional API ?
void putAsync(key, value);
Or a batch API:
void putBatch(Map<K,V> data);
?
Manik Surtani wrote:
> Thinking about this a bit more (and implementing tests, etc for this)
> I think even for the async case we need to do the remote get first
> (and as a side-effect this would provide reliable return values). The
> reason is that not doing this causes txs to behave very weird and
> would need a lot of hacks to behave cleanly without doing the eager get.
>
> Take this example (assuming dist-async)
>
> 1. tx.begin
> 2. putIfAbsent(k) // k exists elsewhere
> 3. get(k) // this will return the OLD val of k, since the tx hasnt
> completed and the owners haven't seen the WriteCommand in 2 yet!
>
> We could hack this to make a record of commands that will be executed
> later, but in the case of conditional writes (like putIfAbsent) we
> dont know if they will succeed. So we could do a get first as well,
> but in this case then we may as well stick with a get-before-write
> approach and thereby provide reliable retvals.
>
> The actual commit would still be 1-phase and async though.
>
> WDYT?
>
> Also, for consistency, I suggest the same for non-tx-writes. This
> then serves the added benefit of removing the weird unsafe flag, etc.
> Ok, so it means doing a remote get before a put, but the cost of this
> is mitigated because a) it is unicast to a small set of servers b)
> the RPC call returns as soon as we get the first valid response and c)
> with MVCC, the get is very quick - no locking needed on the remote end.
>
> Comments?
>
>
> On 21 Apr 2009, at 18:24, Manik Surtani wrote:
>
>>
>> On 21 Apr 2009, at 18:18, Mircea Markus wrote:
>>
>>> Manik Surtani wrote:
>>>>
>>>> On 21 Apr 2009, at 18:01, Mircea Markus wrote:
>>>>
>>>>> yes, indeed. that's what cache.retrieve("key1", "key2",
>>>>> "keyn"...); would do, fetch all the remote values at once
>>>>> (multiple keys mapped to one node will result in one aggregated get).
>>>>>> Sounds pretty clunky though ...
>>>>> Might be. I think it is easy to grasp though, and can have
>>>>> significant benefits for clients that know all the key set they
>>>>> will manipulate in one session.
>>>>
>>>> But the keys retrieved could still be wiped out.
>>>>
>>>> 1. start tx
>>>> 2. retrieve(k1, k2, k3)
>>>> 3. // go make coffee; other processes changing stuff, which
>>>> removes keys from the L1, negating the effect of step 2
>>> Isn't that exactly what happens now with read mvcc entries being
>>> held in context? This won't break neither read_committed nor
>>> repetable_read.
>>
>> Not quite. The return value is calculated atomically when the
>> command is performed, even though the old value is cached in
>> context. E.g., locally,
>>
>> 1. tx.begin
>> 2. read K
>> 3. // go make coffee
>> 4. replace K. This command is atomic and the retval is extracted
>> from the datacontainer as this command is perform()'ed. So what this
>> invocation returns is accurate regardless of interleaving writes
>> between step 2 & 4
>> 5. ...
>>
>>>> 4. replace(k1, v1) // will return incorrect retval. Or will need
>>>> to do a remote get again at this point
>>>> 5. end tx
>>>>
>>>> --
>>>> Manik Surtani
>>>> manik at jboss.org
>>>> Lead, Infinispan
>>>> Lead, JBoss Cache
>>>> http://www.infinispan.org
>>>> http://www.jbosscache.org
>>>>
>>>>
>>>>
>>>>
>>>
>>
>> --
>> Manik Surtani
>> manik at jboss.org
>> Lead, Infinispan
>> Lead, JBoss Cache
>> http://www.infinispan.org
>> http://www.jbosscache.org
>>
>>
>>
>>
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>> infinispan-dev mailing list
>> infinispan-dev at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>
> --
> Manik Surtani
> manik at jboss.org
> Lead, Infinispan
> Lead, JBoss Cache
> http://www.infinispan.org
> http://www.jbosscache.org
>
>
>
>
> _______________________________________________
> infinispan-dev mailing list
> infinispan-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/infinispan-dev
--
Bela Ban
Lead JGroups / Clustering Team
JBoss - a division of Red Hat
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