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
