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From Valentin Kulichenko <valentin.kuliche...@gmail.com>
Subject Re: Multi-cache transactions & persistent store
Date Tue, 02 Aug 2016 02:36:38 GMT
Hi Igor,

In a multi-cache transaction there can several different stores involved,
that's why store is not considered to be self-contained. That's why
transaction callbacks moved to a separate entity - store session listener.

Can you please clarify how do you suggest to use Transaction for this? This
interface is not implemented by a user, so it's not clear to me.

-Val

On Fri, Jul 29, 2016 at 6:40 PM, Igor Rudyak <irudyak@gmail.com> wrote:

> Hi guys,
>
> Playing with Ignite multi-cache transactions(transactions involving
> multiple caches) we run into the lack of proper/easy mechanism to support
> such transactions on persistent store side (while implementing particular
> *CacheStore*).
>
> The problem is there is no easy way for *CacheStore *implementation to get
> information about caches involved in the transaction.
>
> Here are more details:
>
> When committing multi-cache transaction, Ignite produces multiple
> *sessionEnd(...)* calls (in *CacheStore *implementation) - one for each
> cache. Thus to support multi-cache transaction in persistent store, we need
> to accumulate all the changes made to multiple caches (by
> *write/writeAll/delete/deleteAll* operations) and apply them as one
> transaction/batch to a persistent store in the final(last) *sessionEnd
> *call.
> To do this we need to know exact number of caches participating in the
> transaction. Having this number we can skip all *sessionEnd *calls except
> the last - which we will use to commit/persist all the changes we
> previously accumulated.
>
> As for now, the only way to get the number of caches participating in a
> transaction is to register *CacheStoreSessionListener *and count number of
> caches in its "*onSessionStart*" method. Such approach doesn't look very
> elegant cause we always need to keep in mind that specifying "
> *cacheStoreFactory*" in cache configuration is not enough. In addition to
> this we also need to specify appropriate "
> *cacheStoreSessionListenerFactories*" property - otherwise it will not work
> for multi-cache transactions.
>
> Here is an example chunk from cache configuration:
>
> * <property name="cacheStoreFactory">*
> * <bean
>
> class="org.apache.ignite.cache.store.cassandra.CassandraCacheStoreFactory">*
> * <property name="dataSourceBean" value="cassandraDataSource"/>*
> * <property name="persistenceSettingsBean"
> value="cache1_persistence_settings"/>*
> * </bean>*
> * </property>*
> * <property name="cacheStoreSessionListenerFactories">*
> * <list>*
> * <bean class="org.apache.ignite.tests.MyCacheStoreSessionListener"/>*
> * </list>*
> * </property>*
>
> We see that, instead of specifying only one property "*cacheStoreFactory*"
> for a cache we should always specify two properties in case we need
> multi-cache transactions support in persistent store. Conceptually it
> doesn't look good, cause users thinking about *CacheStore *implementation
> like something self-contained - once it specified in cache configuration
> everything should be smooth. But in case of multi-cache transactions
> support we always need to remember about registering some strange
> "listener".
>
> In Ignite we already have such concept as "
> *org.apache.ignite.transactions.Transaction*" which defines our
> transaction. It looks logical if it will also provide information about
> transaction boundaries (caches involved into transaction). Such approach
> can simplify persistent store implementation for multi-cache transactions.
>
> Any thoughts?
>
>
> Igor Rudyak
>

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