# Patent

## Title
System and method for managing an object cache

## Abstract

In order to optimize efficiency of deserialization, a serialization cache is maintained at an object server. The serialization cache is maintained in conjunction with an object cache and stores serialized forms of objects cached within the object cache. When an inbound request is received, a serialized object received in the request is compared to the serialization cache. If the serialized byte stream is present in the serialization cache, then the equivalent object is retrieved from the object cache, thereby avoiding deserialization of the received serialized object. If the serialized byte stream is not present in the serialization cache, then the serialized byte stream is deserialized, the deserialized object is cached in the object cache, and the serialized object is cached in the serialization cache.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority of and is a continuation of U.S. Ser. No. 14/071,998, entitled SYSTEM AND METHOD FOR MANAGING AN OBJECT CACHE, filed on Nov. 5, 2013, now issued U.S. Pat. No. 8,769,203, issued on Jul. 1, 2014, which is a continuation of U.S. Ser. No. 13/598,365, entitled SYSTEM AND METHOD FOR MANAGING AN OBJECT CACHE, filed on Aug. 29, 2012, now issued U.S. Pat. No. 8,583,871, issued on Nov. 12, 2013, which is a continuation of U.S. Ser. No. 13/289,772, entitled SYSTEM AND METHOD FOR MANAGING AN OBJECT CACHE, filed on Nov. 4, 2011, now issued U.S. Pat. No. 8,266,384, issued on Sep. 11, 2012, incorporated herein by reference in their entirety.


FIELD OF THE INVENTION
This disclosure relates to methods of managing the serialized forms of cached objects.
BACKGROUND OF THE INVENTION
Existing serialization solutions typically seek to optimize the effort of serializing an object (for a given protocol) by writing the serialization logic in the most efficient manner possible. Some solutions attempt to avoid redundant serialization by caching complete serialized object graphs, then transmitting these cached object graphs enclosed (opaquely) within another serialization stream. Serialization protocols such as Java object serialization expect the user to provide hand-coded serialization if they wish to optimize.
Increasing the efficiency of a serialization mechanism will always reach an effective limit for a given hardware/software platform, and does not save the effort of repeating serialization for unchanged (or largely unchanged) objects. Enclosing a complete serialization within another serialization stream does not account for references from the outer scope. Hand-coded serialization is tedious for the developer, is error prone, and does not save redundant work.
What is a required is an improved method and system for managing the serialized form of cached objects.
SUMMARY OF THE INVENTION
In order to optimize efficiency of deserialization, a serialization cache is maintained at an object server. The serialization cache is maintained in conjunction with an object cache and stores serialized forms of objects cached within the object cache. When an inbound request is received, a serialized object received in the request is compared to the serialization cache. If the serialized byte stream is present in the serialization cache, then the equivalent object is retrieved from the object cache, thereby avoiding deserialization of the received serialized object. If the serialized byte stream is not present in the serialization cache, then the serialized byte stream is deserialized, the deserialized object is cached in the object cache, and the serialized object is cached in the serialization cache.
In one aspect of the disclosure, there is provided a method for deserializing an object in a server. The method may comprise receiving into the server a serialized object comprising one or more serializations of one or more referenced objects, referencing a serialization cache by the server to determine if one or more of the referenced object serializations are stored by the serialization cache, retrieving referenced objects from an object cache for which the serialization cache stores a serialization for the referenced object, and deserializing portions of the received serialized object that could not be retrieved from the object cache.
In one aspect of the disclosure, there is provided a caching server comprising an object cache, a serialization cache, a request handler and a deserialization module. The request handler may be programmed to receive a remote method invocation request comprising one or more serialized objects from a client and pass the one or more serialized objects to the deserialization module. The deserialization module may be programmed to reference the serialization cache to determine if one or more of the serialized objects are stored by the serialization cache. For serialized objects that are stored by the serialization cache, the deserialization module may retrieve an object corresponding to the serialized object from the object cache. For serialized objects that are not stored by the serialization cache, the deserialization module may deserialize the serialized object, store the deserialized object in the object cache, and store the serialized object in the serialization cache.
In one aspect of the disclosure, there is provided a method for deserializing a serialized object received into a caching server. When the serialized object is received, a serialization cache of the caching server is referenced to determine if the serialized object is stored by the serialization cache. When the serialized object is not stored in the serialization cache, the serialized object is deserialized and stored in an object cache while the serialized object is stored in the serialization cache.



BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made, by way of example only, to specific embodiments and to the accompanying drawings in which:
FIG. 1 shows a caching system;
FIG. 2 shows a process for serializing an object to send to a client;
FIG. 3 shows aggregation of a byte stream;
FIG. 4 a process for deserializing an object;
FIG. 5 shows the process of FIG. 4 incorporating a dedicated caching service;
FIG. 6 provides an indication of the cacheable portions of a byte stream; and
FIG. 7 provides an arrangement of the fields of a byte stream.



DETAILED DESCRIPTION OF THE INVENTION
Serialization costs are usually optimized by protocol choice or algorithmically for a given serialization operation and not by avoiding redundant work between serialization requests of all clients. Where the serialization is cached, it is of a complete object graph delivered as an opaque serialization within a serialization. The average practitioner does not consider serialization costs, being usually more focused on optimizing database retrieval logic. In addition, the average practitioner does not have the skills or knowledge to modify the platform serialization and the average practitioner, being more focused on small-scale page-centric web applications, may not encounter the scaling requirement that would drive the necessity for caching optimization. In addition, serialization formats such as the default Java serialization makes caching of the serialized form difficult (except opaquely).
The present embodiments to be described below seek to reduce the burden of serializing an object graph, where one or more members of that object graph remain largely unchanged between serializations (i.e., cacheable), without altering the serialization protocol.
FIG. 1 shows a system in accordance with an embodiment of the present disclosure. In the system 10, a server includes a request handler 14 for handling object requests from clients 13 for an application 15 that is served by the server 12. The server 12 may serve clients 13 on a variety of protocols and by way of example, FIG. 1 shows a Java serialization client 13a, a Hessian serialization client 13b, an XML serialization client 13c and a JSON serialization client 13d. Other serialization protocols may also be utilized. The server 12 includes a serialization module 16 and a deserialization module 18. The serialization module 16 and deserialization module 18 for a serialization protocol are modified or implemented to interact with an object cache 20 and a serialization cache 22 to minimize serialization effort for objects contained within the object cache. The serialization cache 22 may be a separate module, or a sub-module of the object cache 20 with interactions through the object cache. As will be described in more detail below, the serialization cache 22 maintains a serialized form of objects stored in the object cache 20. While a single serialization cache 22 is shown, the object cache 20 may be related to multiple serialization caches (e.g. one per serialization protocol), in the case where the server 12 serves clients with different protocols (e.g., SOAP web services, JSON web services, RMI clients, CORBA clients, etc.). Multiple serialization caches may be maintained as separate entities or as a single entity, i.e. as a single cache.
In serializing an object graph, the serialization module 16 checks if an object to be serialized is contained within the object cache 20. If the object is present in the object cache 20, then the serialization module 16 sets the current serialization context to reference the serialization cache 22 for that object and its referenced or contained objects. If an object is not found in the serialization cache 22, then the serialization module 16 will populate the serialization cache 22 for that object upon serialization of the object.
The process is performed from the top down, starting with the topmost object in the object graph, and is performed for each object contained by the object graph until the object graph is completely serialized. Aspect-oriented programming techniques may be used to keep the serialization cache in sync with the object cache. The serialization cache will only be as consistent (correct) as the object cache. If the access to the serialization cache is via the object cache (or a caching service), then the object cache/caching service could have that responsibility. The present embodiments deal mainly with consistency of the serialization cache with the object cache. There is the assumption that referenced objects of cached objects are cached.
The object cache might be structured such that references to other cached/cacheable objects are via business key/primary key but field values (primitives, immutables or other contained or referenced objects) are stored directly with the cached object.
Removal of an object from the object cache 20 will trigger a symmetric removal from the serialization cache 22. An update to a cached object will invalidate the portion of the serialization cache corresponding to the field(s) updated when the serialization mechanism allows, otherwise the whole of the cached serialization for that object will be removed. For objects shared by cached objects, the serialization cache will be purged only if the last reference is removed subject to normal caching constraints.
The serialization cache 22 contains the byte arrays containing the full or partial serialized form for objects contained by the object cache 20. The serialization cache 22 is particular to a serialization protocol, and an object cache might be related to multiple serialization caches given the application's requirements.
The serialization cache(s) 22 may be populated on additions and updates to the object cache 20, as well as on demand. In this case, the serialization module 22 is invoked to serialize the objects added to the object cache 20, or serialize the fields modified when objects in the object cache 20 are updated (assuming the serialization allows this, otherwise a complete serialization will be performed). The server may use various proxies, interceptors, “decorators”, code enhancement or other aspect oriented programming techniques as are known to determine that an object state has been modified.
The cached serialization for an object may be supplied by a client. The typical use case for this would be the addition or update of a referenced object. In this case, the deserialization module 18 would interact with the serialization cache 22 and the object cache 20 to add or replace the cached object and the corresponding serialization data for that object. Another option for a new object is to create a temporary store of the serialized form for that object, which then would be moved into the serialization cache 22 upon later addition of that object to the object cache 20.
In the case where the object cache 20 is distributed among multiple servers, the serialization cache 22 could be used to optimize the transmission of the cached objects between the servers. This is also another case where the deserialization module 18 might be used to supply the serialized form for the serialization cache 22.
Optimizations for the serialization cache 22 include population of the cache (or caches) based on the object cache, prior to a client request for the data and modifying only the portion of the serialization cache (or caches) corresponding to changes to the cached object.
With reference now to FIG. 2, there is shown a process flow for handling an outbound requirement from the server 12 to a client 13. The outbound requirement may be in response to a remote invocation from the client or may be a server side push of an object to the client 13. At step 101, the remote application 15 provides an unserialized object to the request handler 14. The request handler passes the object to the serialization module 16 (step 102) which checks the serialization cache 22 for a serialized form of the object(s) (step 103). The serialization cache 22 returns the serialized objects, if available, at step 104. If no serialized forms of the objects exist within the serialization cache, i.e. a cache miss, then the serialization module serializes the objects as normal (step 105). Once the serialization has been performed, the serialization module 16 checks if the object(s) are present in the object cache 20 (Step 106), and if so, saves the serialized form of the cached object(s) in the serialization cache 22 (step 107). The serialization module 16 assembles the serialized form of the object(s), either as retrieved from the cache and/or as serialized presently by the serialization module 16, into a response/push to the client 13 (step 108). The response/push to the client is provided to the request handler (step 109) and then sent on to the client 13 (step 110).
In FIG. 3, there is shown the aggregation of serialized byte stream to be provided to a client. The byte stream 30, which may be only a partial byte stream forming a portion of the entire byte stream to be sent to the client, may include bytes 31 pertaining to a normally serialized object 31, i.e. serialized at the time by the serialization module. The byte stream 30 may also include a serialization of an object 32 retrieved from the serialization cache, an object reference for a normally serialized object 33 and an object reference for a serialized object retrieved from the serialization cache. The byte stream 30 is merely indicative of how different portions of the push to the client can be based on cached and non-cached serializations. An actual byte stream may include some or all of these components. This example shows that the cached serialization is not treated opaquely. A serialized object reference points to a previously (within the byte stream) serialized object.
The serialization cache may also be used to improve the performance of deserialization. FIG. 4 shows a process for processing an inbound request. At step 201, a remote method invocation request is provided from a client 13 to the request handler 14. The request handler 14 passes the serialized method arguments (objects) of the request to the deserialization module (step 202). In this case, the deserialization module 18 matches the bytes to be de-serialized with the serialized bytes stored in the serialization cache 22 (steps 203, 204). Through this match, the deserialization module 18 has a reference to the object within the object cache 20, and need not perform (complete) deserialization for that object. A partial deserialization can aid in making a match, as in deserialization of a primary key or other unique identifier for a business object. The deserialization module 18 can then perform a normal deserialization for the remaining bytes, i.e. for the non-cached objects, and aggregate the cached and non-cached objects and verify the result (step 205). At step 206, the deserialization module 18 checks the object cache 20 and places the missing objects in the cache as well as updating any existing cached objects (step 207). Any newly received or updated serialized objects corresponding to the objects added to the object cache are also added to the serialization cache 22 (step 208). The deserialized method arguments are then returned from the deserialization module 18 to the request handler 14 (step 209) to enable the invocation of the method by the application with the deserialized method arguments (step 210).
On deserialization of an object, the server may recognize a “partial match” and update the changed portions in the serialization cache. This may occur, for example, where a client retrieves an object, updates it, and sends it back. For this, the caches for the object and serialization caches would need to be transactional thereby allowing the server to retrieve the cached object, perform deserialization on the cached object for the changed parts, update the cached object, and update the serialization cache for the changed fields.
In some instances, there may be additional complexity if the “immutables” have been in-lined with the primitives. For the deserialization case, this may require two forms being cached: one where in-lined, one where separate.
In an alternative embodiment, a dedicated caching service may be utilized for controlling the caching of objects and the serialized forms of objects. The serializing module 16 and deserialization module 18 may pass requests to the caching service for analysis with respect to the object cache 20 and serialization cache 22. By way of example, the inbound request of FIG. 4 is depicted in FIG. 5 with the use of a caching service 25. In this case, when the request handler 14 receives a remote method invocation from a client (not shown), the request handler 14 passes the serialized method arguments to the deserialization module 18 (step 301) which checks for matching cached bytes by sending a request to the caching service 25 (step 302). The caching service 25 retrieves any matching bytes from the serialization cache 22 and returns them to the deserialization module 18 (steps 303, 304, 305). The deserialization module 18 performs deserialization on any non-cached bytes and aggregation as described previously (step 306) and provides the serialized form of the objects to the caching service 25 (step 307) for caching. The caching service 25 then performs the previously described steps of placing missing and updated objects in the object cache 20 and update the serialization cache 22 with the serialized objects (steps 308, 309, 310) while the deserialization module 18 returns the deserialized objects to the request handler 14 (step 311) for invoking the method by the application 15 (step 312).
The caching service provides a programmatic interface. The service implementation could either be local or remote or a combination. In one embodiment, at least part of the implementation is local to the application's machine, if not in the same process as the application. Other embodiments include, without limitation:
1. Local implementation, in-process, in-memory cache (object and serialization);
2. Local implementation, in-process, part in-memory, part in stable storage (object in memory, serialization in stable storage, or both part in memory, part in stable storage);
3. Local implementation, in-process, distributed cache;
4. Local implementation, out-of-process, in-memory-cache;
5. Local implementation, out-of-process, part in-memory, part in stable storage cache;
6. Local implementation, out-of-process, distributed cache.
Remote variants of these embodiments are also conceivable.
It can be seen from the foregoing embodiments that the presently described solution speeds the normal serialization of an object. It also can speed deserialization of an object. These enhancements are for a given protocol and are not modifications to that protocol and thus preserve the correct semantics when interacting with unmodified clients. The client, by supplying the serialized form of an object, may in turn speed the operation of the server in serialization and deserialization of that object.
Idiomatic Java server applications using Hibernate as a persistence mechanism will typically employ a second-level cache for reference entities (business domain objects which remain largely unchanged over the life of the application once defined). Objects maintained within this second level cache are natural candidates for inclusion in a serialization cache 22, since for a given serialization protocol, the cacheable portion of the serialized form of the object will remain unchanged so long as the cached object remains unchanged.
Some serialization protocols, like Java object serialization, are not amenable to complete caching when references from the outer scope are considered. FIGS. 6 and 7 detail the portions of the serialized form which are cacheable when using Java serialization. The structure of the serialization cache will differ for each serialization protocol, although some protocols might share the same caching structure.
With reference to FIG. 6, the class descriptor 61, UTF name 62, serial version ID 63, flags 64 and number of fields may be cacheable as a single block. This block may also include the field code 66 and UTF name 67 for the first field. Whether or not the type string 68 of a field is cacheable will depend on the type of field. Similarly, the type code and UTF name for Field 2 and any subsequent fields will be cacheable with the cacheability of the type strings being dependent on the particular field. The block data mode bytes 69 are unlikely to be cacheable because they depend on the total serialization process.
FIG. 7 shows how the fields may be arranged. The fields are arranged first primitives 71, then any immutable fields 72, then other object fields, 73, as shown in FIG. 7. For the Java object serialization protocol, the class descriptor for an object may be altered from the default class descriptor (java.io.ObjectStreamClass) to group primitive “wrapper” objects (e.g., java.lang.Integer) and other immutable value types 72 immediately after the primitive fields 71 to take advantage of the fact that such objects are immutable. If the normal serialization behavior (for Java serialization) to replace duplicate objects with references is ignored, the block of immutable field bytes could be cached and written out following the primitives or cached together with the primitive data block and written as one block. This relaxation of the normal serialization rules and behavior does not require alteration of the deserialization process for the client.
The caching techniques described herein do not modify the “on-the-wire” serialization protocols, only the serialization mechanisms by caching bytes to be directly output to the serialization stream. Importantly, the serialized bytes produced by the described techniques may be interpreted without requiring any modifications at the client side. By contrast, prior art optimization techniques seek to optimize a protocol, or seek to compress the network traffic, which modifies the on the wire format and requires change on the client side, i.e. to decompress. Furthermore, the caching techniques described herein do not prohibit the use of other techniques such as compression, and can be used in conjunction with such techniques as the embodiments deal in the transformation objects to and from uncompressed bytes.
Advantages of the caching of serialized objects includes that it reduces the processing cycles that a server must use to deliver a cached object to a remote client, increasing the ability of the server to handle multiple client requests for cached data. It also does this without altering how the client deserializes the cached object. Fewer CPU cycles may be used to deliver data to a remote client than the typical solutions, and it integrates the cached serialized data within a serialization stream rather than embedding it as a “stream within a stream”.
The components of the system may be embodied in hardware, software, firmware or a combination of hardware, software and/or firmware. In a hardware embodiment, the caching server may include one or more processors operatively associated with one or more memories. The memory may store instructions that are executable on the processor for deploying the caching methods described above.
Although embodiments of the present invention have been illustrated in the accompanied drawings and described in the foregoing description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims. For example, the capabilities of the invention can be performed fully and/or partially by one or more of the blocks, modules, processors or memories. Also, these capabilities may be performed in the current manner or in a distributed manner and on, or via, any device able to provide and/or receive information. Further, although depicted in a particular manner, various modules or blocks may be repositioned without departing from the scope of the current invention. Still further, although depicted in a particular manner, a greater or lesser number of modules and connections can be utilized with the present invention in order to accomplish the present invention, to provide additional known features to the present invention, and/or to make the present invention more efficient. Also, the information sent between various modules can be sent between the modules via at least one of a data network, the Internet, an Internet Protocol network, a wireless source, and a wired source and via plurality of protocols.

## Claims

1. A method, comprising:
when a serialization cache does not store one or more referenced objects, performing:
deserializing the one or more referenced objects;
storing a serialized byte stream for the one or more referenced objects in the serialization cache;
determining if one or more immutable objects are provided inline with one or more primitive objects in the serialized byte stream; and
where one or more immutable objects are provided inline with one or more primitive objects in the serialized byte stream performing at least one of:
storing a first form of the serialized byte stream in the serialization cache in which the one or more immutable objects are inline with the one or more primitive objects; and
storing a second form of the serialized byte stream in the serialization cache in which the one or more immutable objects are cached separately from the one or more primitive objects.

2. The method of claim 1 comprising storing the one or more referenced objects in the object cache when the serialization cache does not store the one or more referenced objects.

3. The method of claim 1 comprising associating the stored serialized byte stream with the corresponding cached object.

4. The method of claim 1 comprising at least one of:
retrieving referenced objects from an object cache for which the serialization cache stores a serialization for the referenced object; and
deserializing portions of the serialized object that could not be retrieved from the object cache.

5. The method of claim 1 comprising determining if one or more serializations of the one or more referenced objects are stored by the serialization cache, wherein determining if one or more referenced object serializations are stored by the serialization cache comprises determining if one or more byte streams stored in the serialization cache at least partially match a byte stream of the received serialized object.

6. The method of claim 1 comprising invoking a method passing as an argument the deserialized object comprising one or more objects retrieved from the object cache.

7. A server, comprising:
an object cache;
a serialization cache; and
a deserialization module;
for serialized objects that are not stored by a serialization cache, the deserialization module is configured to:
deserialize the serialized object;
store the serialized object in the serialization cache;
determine if one or more immutable objects are provided inline with one or more primitive objects in a serialized byte stream; and
where one or more immutable objects are provided inline with one or more primitive objects in the serialized byte stream perform at least one of:
store a first form of the serialized byte stream in the serialization cache in which the one or more immutable objects are inline with the one or more primitive objects; and
store a second form of the serialized byte stream in the serialization cache in which the one or more immutable objects are cached separately from the one or more primitive objects.

8. The server of claim 7 comprising a serialization module configured to:
determine an object to provide to a client;
determine if the object is cached in the object cache;
when the object is cached in the object cache, retrieve a corresponding serialization of the object from the serialization cache; and
provide the retrieved serialization of the object to the client.

9. The server of claim 7 comprising a serialization module configured to:
determine an object to provide to a client;
determine if the object is cached in the object cache;
when the object is not cached in the object cache, serialize the object; and
provide the serialized object to the client.

10. The server of claim 9 wherein the serialization module is configured to:
store the serialized object in the serialization cache; and
store the object in the object cache.

11. The server of claim 7 wherein the serialization cache is maintained for a plurality of serialization protocols.

12. The server of claim 7 comprising a plurality of serialization caches for a plurality of serialization protocols.

13. The server of claim 7 wherein for serialized objects that are not stored by the serialization cache: store the deserialized object in the object cache.

14. A method, comprising:
determining if one or more immutable objects are provided inline with one or more primitive objects in a serialized byte stream; and
where one or more immutable objects are provided inline with one or more primitive objects in the serialized byte stream, performing at least one of:
storing a first form of the serialized byte stream in the serialization cache in which the one or more immutable objects are inline with the one or more primitive objects; and
storing a second form of the serialized byte stream in the serialization cache in which the one or more immutable objects are cached separately from the one or more primitive objects.

15. The method of claim 14 comprising:
determining that a deserialized object is an updated object stored in the cache;
updating the cache with the deserialized object; and
updating the corresponding serialized form of the deserialized object in the serialization cache.

16. The method of claim 14 comprising:
deserializing an object identifier from the serialized object;
determining from the object identifier if the object is stored in the object cache.

17. The method of claim 16 comprising continuing with the remainder of the deserialization of the serialized object only when it is determined from the object identifier that the object is not stored in the cache.

18. The method of claim 14 comprising, when the serialized object is stored in the serialization cache, retrieving an object corresponding to the serialized object from an object cache.

19. The method of claim 14 comprising retrieving referenced objects from an object cache for which the serialization cache stores a serialization for the referenced object.

20. The method of claim 14 wherein when the serialized object is not stored in the serialization cache performing at least one of:
deserializing the object;
storing the deserialized object in an object cache; and
storing the received serialized object in the serialization cache.