Abstract:
A method, an apparatus, and computer instructions are provided for a context based cache infrastructure to enable subset query over a cached object. Responsive to detecting a query to a root context of a context tree, the tree is traversed for a parent context of a subcontext corresponding to the name and value pair, which is identified by a user in the query. If the parent context caches all query results, the query results are iterated and the remaining name and value pairs are filtered out. However, if the parent context does not cache all query results, the traversing step is repeated for next parent context of the subcontext until a root context is encountered. If a root context is encountered, a query is issued to the database for the name and value pair and the result of the database query is cached in a new context.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to an improved data processing system. In particular, the present invention relates to cached object returned from a database query. Still more particular, the present invention relates to a context based cached infrastructure that enables a subset query over the cached object returned from a database query in a data processing system.  
         [0003]     2. Description of Related Art  
         [0004]     In the current enterprise JavaBeans™ (EJB) specification, lifecycle methods are provided for managing an entity bean&#39;s lifecycle. Examples of lifecycle methods include ejbCreate, which manages the creation of entity beans; ejbStore, which manages update of entity beans; and ejbRemove, which manages removal of entity beans. An entity bean is an enterprise JavaBean™ that has a physical data representation in a data store, for example, a row in a relational database table. Enterprise JavaBean™ or J2EE is a product available from Sun Microsystems, Inc.  
         [0005]     In addition to lifecycle methods, enterprise JavaBeans™ specification provides ejbFind and ejbSelect methods to query entity beans that satisfy a search condition. For applications that seldom update their data, it is more efficient to cache the data locally rather than querying the database each time an update occurs, since database queries affect application performance.  
         [0006]     Currently, query results may be cached and a user may search the query results by a certain criteria. For example, a catalog may have a “product” field and a “type” field, a user may search by the product, such as product=“electronics” or product=“books”. Since the catalog is seldom updated, the query results may be cached by the criteria, such that when the user performs the same search, the result is returned from the cached object instead of the database, thus, improving the search response time. If query results are cached without context, for each query, data may be returned if and only if it is an exact match.  
         [0007]     Currently, no existing mechanism is present that allows a search to be performed on the subset of the existing cached query results. For example, to perform a search on query results returned by product=“books” for type=“bestsellers”. If all the “books” are already cached, it is more efficient to iterate the result of “books” and filter them to retrieve the “bestsellers”, rather than performing a separate search on the database based on the product and type.  
         [0008]     In addition, no existing mechanism is available that sets up query results in such a way that makes it easy for user to iterate and filter query results. Therefore, it would be advantageous to have an improved method for a context based cache infrastructure that enables subset query over a cached object, such that database queries may be minimized to improve search performance.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a method, an apparatus, and computer instructions for a context based infrastructure to enable subset query over a cached object. The mechanism of the present invention detects a query to a root context of a context tree from a user, wherein the query includes a name and value pair. Responsive to detecting the query, the mechanism traverses the context tree for a parent context of a subcontext corresponding to the name and value pair, and determines if the parent context caches all query results.  
         [0010]     If the parent context does not cache all query results, the mechanism repeats the traversing step for next parent context of the subcontext until a root context is encountered. When a root context is encountered, the mechanism issues a query to the database for the name and value pair, and caches the result of the database query in a new context.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0011]     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0012]      FIG. 1  is a pictorial representation of a network of data processing systems in which the present invention may be implemented in accordance with a preferred embodiment of the present invention;  
         [0013]      FIG. 2  is a block diagram of a data processing system that may be implemented as a server in which the present invention may be implemented in accordance with a preferred embodiment of the present invention;  
         [0014]      FIG. 3  is a block diagram illustrating a data processing system in which the present invention may be implemented in accordance with a preferred embodiment of the present invention;  
         [0015]      FIG. 4  is a diagram illustrating an exemplary context tree cached by the mechanism of the present invention for a query result in accordance with an illustrative embodiment of the present invention;  
         [0016]      FIG. 5  is a diagram illustrating data structures representing root context  400 , subcontexts  402 , and  404  in  FIG. 4  in accordance with an illustrative embodiment of the present invention; and  
         [0017]      FIG. 6  is a flowchart of an exemplary process for context based cache infrastructure to enable subset query over a cached object in accordance with an illustrative embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     With reference now to the figures,  FIG. 1  depicts a pictorial representation of a network of data processing systems in which the present invention may be implemented. Network data processing system  100  is a network of computers in which the present invention may be implemented. Network data processing system  100  contains a network  102 , which is the medium used to provide communications links between various devices and computers connected together within network data processing system  100 . Network  102  may include connections, such as wire, wireless communication links, or fiber optic cables.  
         [0019]     In the depicted example, server  104  is connected to network  102  along with storage unit  106 . In addition, clients  108 ,  110 , and  112  are connected to network  102 . These clients  108 ,  110 , and  112  may be, for example, personal computers or network computers. In the depicted example, server  104  provides data, such as boot files, operating system images, and applications to clients  108 - 112 . Clients  108 ,  110 , and  112  are clients to server  104 . Network data processing system  100  may include additional servers, clients, and other devices not shown. In the depicted example, network data processing system  100  is the Internet with network  102  representing a worldwide collection of networks and gateways that use the Transmission Control Protocol/Internet Protocol (TCP/IP) suite of protocols to communicate with one another. At the heart of the Internet is a backbone of high-speed data communication lines between major nodes or host computers, consisting of thousands of commercial, government, educational and other computer systems that route data and messages. Of course, network data processing system  100  also may be implemented as a number of different types of networks, such as for example, an intranet, a local area network (LAN), or a wide area network (WAN).  FIG. 1  is intended as an example, and not as an architectural limitation for the present invention.  
         [0020]     Referring to  FIG. 2 , a block diagram of a data processing system that may be implemented as a server, such as server  104  in  FIG. 1 , is depicted in accordance with a preferred embodiment of the present invention. Data processing system  200  may be a symmetric multiprocessor (SMP) system including a plurality of processors  202  and  204  connected to system bus  206 . Alternatively, a single processor system may be employed. Also connected to system bus  206  is memory controller/cache  208 , which provides an interface to local memory  209 . I/O Bus Bridge  210  is connected to system bus  206  and provides an interface to I/o bus  212 . Memory controller/cache  208  and I/O Bus Bridge  210  may be integrated as depicted.  
         [0021]     Peripheral component interconnect (PCI) bus bridge  214  connected to I/O bus  212  provides an interface to PCI local bus  216 . A number of modems may be connected to PCI local bus  216 . Typical PCI bus implementations will support four PCI expansion slots or add-in connectors. Communications links to clients  108 - 112  in  FIG. 1  may be provided through modem  218  and network adapter  220  connected to PCI local bus  216  through add-in connectors.  
         [0022]     Additional PCI bus bridges  222  and  224  provide interfaces for additional PCI local buses  226  and  228 , from which additional modems or network adapters may be supported. In this manner, data processing system  200  allows connections to multiple network computers. A memory-mapped graphics adapter  230  and hard disk  232  may also be connected to I/O bus  212  as depicted, either directly or indirectly.  
         [0023]     Those of ordinary skill in the art will appreciate that the hardware depicted in  FIG. 2  may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention.  
         [0024]     The data processing system depicted in  FIG. 2  may be, for example, an IBM eServer pSeries system, a product of International Business Machines Corporation in Armonk, N.Y., running the Advanced Interactive Executive (AIX) operating system or LINUX operating system.  
         [0025]     With reference now to  FIG. 3 , a block diagram illustrating a data processing system is depicted in which the present invention may be implemented. Data processing system  300  is an example of a client computer. Data processing system  300  employs a peripheral component interconnect (PCI) local bus architecture. Although the depicted example employs a PCI bus, other bus architectures such as Accelerated Graphics Port (AGP) and Industry Standard Architecture (ISA) may be used. Processor  302  and main memory  304  are connected to PCI local bus  306  through PCI Bridge  308 . PCI Bridge  308  also may include an integrated memory controller and cache memory for processor  302 . Additional connections to PCI local bus  306  may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter  310 , small computer system interface (SCSI) host bus adapter  312 , and expansion bus interface  314  are connected to PCI local bus  306  by direct component connection. In contrast, audio adapter  316 , graphics adapter  318 , and audio/video adapter  319  are connected to PCI local bus  306  by add-in boards inserted into expansion slots. Expansion bus interface  314  provides a connection for a keyboard and mouse adapter  320 , modem  322 , and additional memory  324 . SCSI host bus adapter  312  provides a connection for hard disk drive  326 , tape drive  328 , and CD-ROM drive  330 . Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors.  
         [0026]     An operating system runs on processor  302  and is used to coordinate and provide control of various components within data processing system  300  in  FIG. 3 . The operating system may be a commercially available operating system, such as Windows XP, which is available from Microsoft Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provide calls to the operating system from Java programs or applications executing on data processing system  300 . “Java” is a trademark of Sun Microsystems, Inc. Instructions for the operating system, the object-oriented programming system, and applications or programs are located on storage devices, such as hard disk drive  326 , and may be loaded into main memory  304  for execution by processor  302 .  
         [0027]     Those of ordinary skill in the art will appreciate that the hardware in  FIG. 3  may vary depending on the implementation. Other internal hardware or peripheral devices, such as flash read-only memory (ROM), equivalent nonvolatile memory, or optical disk drives and the like, may be used in addition to or in place of the hardware depicted in  FIG. 3 . Also, the processes of the present invention may be applied to a multiprocessor data processing system.  
         [0028]     As another example, data processing system  300  may be a stand-alone system configured to be bootable without relying on some type of network communication interfaces As a further example, data processing system  300  may be a personal digital assistant (PDA) device, which is configured with ROM and/or flash ROM in order to provide non-volatile memory for storing operating system files and/or user-generated data.  
         [0029]     The depicted example in  FIG. 3  and above-described examples are not meant to imply architectural limitations. For example, data processing system  300  also may be a notebook computer or hand held computer in addition to taking the form of a PDA. Data processing system  300  also may be a kiosk or a Web appliance.  
         [0030]     The processes and mechanisms of the present invention may be implemented as computer instructions executed by processor  302  in data processing system  300  in  FIG. 3 , or processors  202  and  204  in data processing system  200  in  FIG. 2 .  
         [0031]     The present invention provides a method, an apparatus, and computer instructions for a context based cache infrastructure to enable subset query over cached object. The present invention provides a mechanism that enables in-memory or cached object query by constructing the cache as a context tree. The context tree includes a root cache context, ‘/’, for each EJB type. The root cache context can hold objects that belong to the EJB type without any filtering. For example, a root cache context may hold the entire catalog data returned from catalog.findAll( ) query.  
         [0032]     Each root cache context may include sub contexts, which indicate detailed filtering of cached results of the current root cache context by a group of field name/field value pairs. For example, an EJB type “catalog” may include a “product” field and a “type” field, and a root cache context ‘/’ may include sub context ‘/product/books’, which hold objects returned from catalog.findbyProduct(“book”) query. Sub context ‘/product/books’ may also include its sub context ‘/product/books/types/bestsellers’, which hold objects returned from catalog.findByProductAndType(“books”, “bestsellers”) query.  
         [0033]     When a query is detected by the mechanism of the present invention, a findContext( ) method is called to the root cache context with a field name and field pair pairs, for example, {“product”, “book”} (“type”, “bestsellers”). In turn, a context at the level of ‘/product/book/type/bestsellers’ is returned. The mechanism of the present invention then traverses the parents of ‘/product/book/type/bestsellers’ context until it reaches the root cache context to identify the nearest context that cached the query results.  
         [0034]     In the above example, the mechanism of the present invention traverses first in subcontext ‘/product/book’, and then in root cache context ‘/’. If a parent context that cached query results is found, the mechanism of the present invention iterates the cached results of the upper level and filters out the remaining field name and field value pairs, that is, the original field name and value pairs excluding the upper level context represented. However, if no parent context is found, the mechanism of the present invention issues a query to the database and caches the result at the new context level.  
         [0035]     Turning now to  FIG. 4 , a diagram illustrating an exemplary context tree cached by the mechanism of the present invention for a query result is depicted in accordance with an illustrative embodiment of the present invention. As shown in  FIG. 4 , for each EJB type, the mechanism of the present invention creates a root cache context. In this example, root context ‘/’  400  includes all catalog data returned from a Catalog.findAll( ) query.  
         [0036]     Root cache context  400  has subcontext that indicates detail filtering of cache result by a group of field name/field value pair. In this example, root cache context  400  has subcontext ‘/product/books’  402 , which hold objects filtered from a Catalog.findByProduct(“book”) subset query. In turn, subcontext ‘/product/books’  402  has a subcontext ‘/product/books/type/bestsellers’  404  that hold objects filtered from a Catalog.findByProductAndType(“books”,“bestseller”) subset query.  
         [0037]     Turning now to  FIG. 5 , a diagram illustrating data structures representing root context  400 , subcontexts  402 , and  404  in  FIG. 4  is depicted in accordance with an illustrative embodiment of the present invention. As shown in  FIG. 5 , catalog  500  includes two fields, product  502  and type  504 . Catalog  500  represents root cache context  400  in  FIG. 4 .  
         [0038]     Product field  502  has a set of fields, including books  506 , CDs  508 , and magazines  510 . Books  506  represents subcontext ‘/product/books’  402  in  FIG. 4 . In addition, type fields  504  has a set of fields, including bestsellers  512 , hard cover  514 , and soft cover  516 . Bestsellers  512  represent ‘/product/books/type/bestsellers’  404  in  FIG. 4 . Bestsellers  512  include a number of entries, including Good Story  518  and Great Book  520 . These are entries that are returned when subset query Catalog.findByProductAndType(“books”,“bestsellers”) is filtered.  
         [0039]     Turning now to  FIG. 6 , a flowchart of an exemplary process for context based cache infrastructure to enable subset query over a cached object is depicted in accordance with an illustrative embodiment of the present invention. As shown in  FIG. 6 , the process begins when a user issues a query to the root cache context of the context tree with the field name and value pair (step  600 ). An example of the field name and field value pair may be {“product”, “book”} {“type”, “bestsellers”}.  
         [0040]     Next, the mechanism of the present invention traverses the parent of the subcontext according to the field name and value pair (step  602 ). A determination is then by the mechanism as to whether the parent context caches all query results (step  604 ). If the parent context has all query results, the mechanism of the present invention iterates the cache result of the parent context and filters out the remaining field name and value pairs (step  608 ). The process then terminates.  
         [0041]     However, if the parent context does not have all query results, the mechanism of the present invention then makes a determination as to whether the parent context is the root context (step  606 ). This means that the root context has been reached. If the parent context is not the root context, the mechanism traverses to the next parent context up the context tree (step  610 ). However, if the parent context is the root context, the mechanism of the present invention issues a query to the database and caches the query result in a new context (step  612 ) and the process terminates thereafter.  
         [0042]     In summary, the present invention provides a context based infrastructure to enable subset query over a cached object. By using the mechanism of the present invention, a user may now iterate and filter query results. In addition, database queries may now be minimized to improve search performance.  
         [0043]     It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular data processing system.  
         [0044]     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.