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Hibernate is a high-performance Object/Relational persistence and query service which is licensed under the open source GNU Lesser General Public License (LGPL). Hibernate not only takes care of the mapping from Java classes to database tables (and from Java data types to SQL data types), but also provides data query and retrieval facilities. Hibernate provides 3 types of caching.

The session cache caches object i.e. entity, within the current session. It is enabled by default in Hibernate. Objects in the session cache reside in the same memory location.

The second level cache, an optional cache is responsible for caching objects across sessions. When this is turned on, objects will be first searched in cache and if they are not found, a database query will be fired. Second level cache will be used when the objects are loaded using their primary key. This includes fetching of associations. In case of second level cache, the objects are constructed and hence all of them will reside in different memory locations.

Query Cache is used to cache the results of a query. By default, the query cache is optional. When the query cache is turned on, the results of the query are stored against the combination of query and parameters. Every time the query is fired the cache manager checks for the combination of parameters and query. If the results are found in the cache they are returned otherwise a database transaction is initiated.

Hibernate Caching functionality is designed to reduce the amount of necessary database access. When the objects are cached they reside in memory. You have the flexibility to limit the usage of memory and store the items in disk storage.

Whenever a hibernate session tries to load an entity, the first level cache is searched for the cached copy of the entity. The first level cache returns the result to the session if the cached entity is found. If the first level cache does not possess the entity, the second level cache is searched for that entity. If the entity is found in the second level cache, then the entity is served from it. If not, a query is executed to retrieve the entity. If the query under execution has previously cached results, then the result of the query is retrieved from the query cache and the cached entity identifiers are used to access the second level cache. If the query was not executed earlier, a query is fired to the database. Once the entity is returned as a response, it is stored in both first level cache and the second level cache before being returned as a response. If any changes were made directly to the database, then the second level cache needs to be updated with the modified entities. If the second level cache is not updated for a prolonged time period, then the queries served by the cache may contain obsolete entities. In the XenMobile environment, this may cause old policies and application lists to be pushed to the user devices, which in turn may pose a serious security thread to the mobile data. Also, if the cache is not sized adequately, it may not be able to hold many entities, resulting in a high ratio of cache misses. This will in turn increase direct database accesses, which in itself is a performance spoiler! Moreover, query execution may also take longer than normal, impacting user experience with the XenMobile server. To avoid such unpleasant eventualities, administrators should constantly monitor the usage and overall performance of the Hibernate cache. This is where the XMHibCacheTest test helps.

This test tracks the requests to cache and notifies administrators if a large number of requests were not serviced by the cache. This test also points you to the queries that took too long to execute, thus enabling administrators to nail the root-cause of any slowness that may be experienced by XenMobile users. This way, this test provides you with effective pointers to optimize cache usage and enhance the performance of the XenMobile server.

Measurement	Description	Measurement Unit	Interpretation
load_count	Indicates the number of times the collections were loaded.	Number	The detailed diagnosis of this measure if enabled, lists the name of the each collection and the number of times each collection was loaded.
fetch_count	Indicates the number of times the collections were fetched.	Number	The detailed diagnosis of this measure if enabled, lists the name of the collection and the number of times each collection was fetched.
recreate_count	Indicates the number of times the collections were recreated.	Number	The detailed diagnosis of this measure if enabled, lists the name of each collection and the number of times each collection was recreated.
update_count	Indicates the number of times the collections were updated.	Number	The detailed diagnosis of this measure if enabled, lists the name of the collection and the number of times each collection was updated.
remove_count	Indicates the number of times the collections were removed.	Number	The detailed diagnosis of this measure if enabled, lists the name of each collection and the number of times each collection was removed.

This test will report the following metrics for the Entities descriptor:

Measurement	Description	Measurement Unit	Interpretation
load_count	Indicates the number of times the entities were loaded.	Number	The detailed diagnosis of this measure if enabled, lists the name of each entity and the number of times each entity was loaded.
fetch_count	Indicates the number of times the entities were fetched.	Number	The detailed diagnosis of this measure if enabled, lists the name of each entity and the number of times each entity was fetched.
update_count	Indicates the number of times the entities were updated.	Number	The detailed diagnosis of this measure if enable, lists the name of the entity and the number of times each entity was updated.
insert_count	Indicates the number of entity inserts.	Number	The detailed diagnosis of this measure if enabled, lists the name of the entity and the number of times each entity was inserted.
delete_count	Indicates the number of times the entities were deleted.	Number	The detailed diagnosis of this measure if enabled, lists the nale of the entity and the number of times each entity was deleted.

This test will report the following metrics for the Queries descriptor:

Measurement	Description	Measurement Unit	Interpretation
cache_hit_count	Indicates the number of queries that were successfully retrieved from the queries cache.	Number	A high value is desired for this measure. The detailed diagnosis of this measure if enabled, lists the query and the number of times each query was successfully retrieved.
cache_miss_count	Indicates the number of queries that were not available in the queries cache.	Number	The detailed diagnosis of this measure if enabled, lists the queries and the number of times each query was not available in the cache.
cache_put_count	Indicates the number of cacheable queries put in the queries cache.	Number	The detailed diagnosis of this measure if enabled, lists the queries and the number of times cacheable queries were put in the cache.
exe_avg_time	Indicates the average time taken to execute the queries in the queries cache.	Seconds	A low value is desired for this measure. The detailed diagnosis of this measure if enabled, lists the name of the query and the time taken to execute the query.
exe_count	Indicates the total number of queries executed from the queries cache.	Number	The detailed diagnosis of this measure if enabled, lists each query that was executed and number of times each query was executed.
exe_max_count	Indicates the maximum time taken to execute a query in the queries cache i.e., the time taken to execute the slowest recorded query.	Number	A sudden/gradual increase in the value of this measure is a cause of concern. When a query takes too long to execute, the subsequent queries should wait for a longer time thus resulting in delayed execution of the queries. When the execution of the queries take too longer than usual, or when a query is being executed indefinitely, then it may directly impact the performance of the XenMobile server which when left unattended may impact the overall performance of the target environment resulting in poor end user experience. The detailed diagnosis of this measure if enabled, lists each query that was executed and the maximum time taken for execution.
exe_min_count	Indicates the minimum time taken to execute a query in the queries cache i.e., the time taken to execute the fastest recorded query.	Number	The detailed diagnosis of this measure if enabled, lists each query and the minimum time taken for executing each query.
exe_row_count	Indicates the number of rows returned by the queries cache after execution of the queries.	Number	The detailed diagnosis of this measure if enabled, lists each query and the number of rows that were returned after execution.

This test will report the following metrics for the Second Level descriptor:

Measurement	Description	Measurement Unit	Interpretation
cache_hit_count	Indicates the number of cacheable entities/collections that were successfully retrieved from the second level cache.	Number	A high value is desired for this measure. The detailed diagnosis of this measure if enabled, lists the name of the cacheable entities/collections and the number of times the entities/collections were successfully retrieved.
cache_miss_count	Indicates the number of cacheable entities/collections that were not available in the second level cache.	Number	The detailed diagnosis of this measure if enabled, lists the name of the cacheable entities/collections and the number of times the entities/collections were not available in the cache.
cache_put_count	Indicates the number of cacheable entities/collections put in the second level cache.	Number	The detailed diagnosis of this measure if enabled, lists the name of the cacheable entities/collections and the number of times the entities/collections were put in the cache.
memory_element_count	Indicates the number of cacheable entities/collections stored in the memory of the second level cache.	Number	The detailed diagnosis of this measure if enabled, lists the cacheable entities/collections and the number of times each entity/collection was stored in the memory.
disk_element_count	Indicates the number of cacheable entities/collections stored on the disk of the second level cache.	Number	The detailed diagnosis of this measure if enabled, lists the cacheable entities/collections and the number of times each entity/collection was stored in the disk.
size_in_memory	Indicates the total size of the cacheable entities in the memory of the second level cache.	MB	The detailed diagnosis of this measure if enabled, lists the name of the entity and the size of the entity in the memory of the cache.

This test will report the following metrics for the Summary descriptor:

Measurement	Description	Measurement Unit	Interpretation
connect_count	Indicates the total number of JDBC connections requested by the sessions.	Number
flush_count	Indicates the total number of flushes executed by the sessions (either explicit or implicit).	Number	The detailed diagnosis of this measure if enabled, lists the name of the cacheable entities/collections and the number of times the entities/collections were not available in the cache.
close_statement_count	Indicates the number of prepared statements that were released.	Number	A high value for this measure may result in a lot of additional queries which may hinder the performance of the Hibernate cache.
session_open_count	Indicates the number of sessions that were opened.	Number
session_close_count	Indicates the number of sessions that were closed.	Number
transaction_count	Indicates the total number of transactions.	Number
success_trans_count	Indicates the number of transactions that were successful.	Number
opt_failure_count	Indicates the number of optimistic lock exceptions.	Number
prepare_stmt_count	Indicates the number of prepared statements acquired.	Number	A high value for this measure may result in a lot of additional queries which may hinder the performance of the Hibernate cache.
query_exec_count	Indicates the number of times the queries have been executed for this cache type.	Number
query_exec_max_timet	Indicates the total size of the cacheable entities in the memory of the second level cache.	Millisecs	A low value is desired for this measure. If there is a sudden/gradual increase in the value of this measure, then it indicates a performance bottleneck which may be due to connectivity issues in the database or unnecessary execution of additional queries by the statements. The detailed diagnosis of this measure if enabled, lists the name of each query and the maximum time taken to execute the query.